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Impact of tobacco management practices on soil, water and nutrients losses in steeplands with shallow soil
Catena 183 (2019) 104215
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Impact of tobacco management practices on soil, water and nutrients losses in steeplands with shallow soil
T
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José Miguel Reicherta, , André Pellegrinib, Miriam Fernanda Rodriguesa, Tales Tiecherc, Danilo Rheinheimer dos Santosa a
Department of Soil Science, Universidade Federal de Santa Maria (UFSM), 97105-900 Santa Maria, Rio Grande do Sul State, Brazil Universidade Tecnológica Federal do Paraná, 97105-490 Dois Vizinhos, Paraná State, Brazil c Department of Soil Science, Faculty of Agronomy, Interdisciplinary Research Group on Environmental Biogeochemistry (IRGEB), Universidade Federal do Rio Grande do Sul, 91540-000 Porto Alegre, Rio Grande do Sul State, Brazil b
A R T I C LE I N FO
A B S T R A C T
Keywords: Intensive tillage Conservation practices Erosion Sediment contamination Nutrient loss
Tobacco is produced in Brazil mainly by small farmholders, on shallow soils on steeplands or on sandy soils, usually under intense soil tillage and lacking soil conservation measures, which can result in large losses of water, soil and nutrients such as P and K. We studied soil management systems for tobacco cropped using animal traction, on shallow soil on steeplands. On a Leptosol, we evaluated conventional tillage (CT), minimum tillage after fallow (MTf), minimum tillage after oat (MTo), no-tillage without ridge (NT), no-tillage with ridge (NTr) and no-tillage with consolidated ridge (NTrc), in a completely randomized blocks design with three replicates. Runoff plots of 1.2 m2 were used to determine water and soil loss by runoff, and total and soluble P and K losses in eight rainfall events during the tobacco crop cycle. Oat cultivation prior to tobacco provided higher dry-mass mulch production and the lowest proportion of exposed soil and rocks in NTr, NTrc and NT systems. The losses of water and of P and K in the soluble forms during the storm rainfall events evaluated were lower for NT management compared to the other treatments. Total soil loss for the monitored rainfall-events was 15 and 16 Mg ha−1 for CT and MTf management, and it was reduced about five times for MTo, NTrc and NTr treatments. However, the lowest soil loss was observed for NT (0.2 Mg ha−1). This same trend was observed for total losses of P and K, where NT reduced about 97 and 57 times the losses of these nutrients compared to CT. Therefore, these results show that conservation managements such as no-tillage or minimum tillage associated with winter cover crops without grounding of tobacco seedlings may be effective to reduce soil losses along with P and K adsorbed in the soil. However, reduction of losses of water, soluble and total P and K was only effective combining notillage with no ridge construction and winter cover crop.
1. Introduction Brazil was the world leader in tobacco (Nicotiana tabacum L.) exports in the 2011/2012 agricultural year, and the second place in production with more than 500 thousand tons in 2015/2016. In the three southern States, tobacco farming was the main agricultural activity of approximately 144 thousand families that grow 271 thousand hectares (Afubra, 2016) in an integrated system between familyfarmers and international agro-industries. Tobacco production is mainly carried out in regions with large numbers of families and labor availability in small farming units, in two types of agroecological conditions: (i) sloping areas naturally unsuitable for annual crops, due to the presence of shallow soils (Dalmolin et al.,
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2003) and highly susceptible to erosion (Bonumá et al., 2014), and (ii) sandy soils of low resistance to degradation (Reichert et al., 2016). In both environments, tobacco is cultivated with intense soil tillage and lack of conservation practices in most of the cultivated areas (Merten and Minella, 2006). Leaves are the commercial product of high added-value and have, thus, been the sole focus of tobacco genetic improvement. Tobacco root system has little absorption surface (thick, sparsely branched roots with very few roots - Rheinheimer et al., 1994) and nutrient absorption capacity, especially phosphorus (low maximum inflow of P, and high minimum concentration of P in the solution for absorption - Petry et al., 1994), thus requiring high doses of fertilizers and tillage to loosen the soil. Moreover, tobacco roots are not tolerant to limited-drainage and
Corresponding author. E-mail address: [email protected] (J.M. Reichert).
https://doi.org/10.1016/j.catena.2019.104215 Received 21 March 2019; Received in revised form 12 July 2019; Accepted 5 August 2019 0341-8162/ © 2019 Elsevier B.V. All rights reserved.
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2. Material and methods
compacted soils (Alameda et al., 2012; Turšić et al., 2016). Soil tillage is an essential practice to obtain adequate tobacco yield. Nevertheless, there is a strong contradiction between tilling the whole field and the need for ridge construction, since tobacco root growth between crop rows is reduced. Furthermore, there is intense human, animal or mechanized traffic between crop lines to perform phytosanitary treatments and, particularly, leaves harvesting. The crop does not provide soil coverage along the crop cycle and favors soil exposure to erosive processes. In conventional tillage for tobacco on steeplands, animal-driven plowing moves soil from the top of the field downward. Thus, there is a net soil translocation on the hillslope due to tillage operations, exposing subsoil at the crest while burying soil at the bottom. With tillage erosion no soil has to leave the field, but the effects for productivity and increased yield variability can be significant. The combination of cultivating agroecologically fragile lands, intense soil tillage, high nutrient supply, and roots with inefficient absorption capacity lead to increased tobacco production costs and high environmental contamination. High erosion rates and water contamination with sediments (Merten and Minella, 2006; Minella et al., 2009; Oliveira et al., 2012) and agrochemicals (Pellegrini et al., 2010; Kaiser et al., 2010, 2015) characterize rural watersheds where tobacco is the main cash crop. Erosion and contamination are significant in tobacco cultivation, since the season of soil tillage coincides with high-erosivity rainfall (Ramon et al., 2016). Erosive rains on bare soil cause intense erosion, soil degradation, reduction of productive capacity, high sediment yield, and contamination of water resources (Merten and Minella, 2006; Minella et al., 2009; Bagio et al., 2017; Bertol et al., 2017). Concentration of P and K in runoff varies mainly with its solubility in water and its concentration in soil, which is influenced by fertilization, management, and soil type (Mendonça et al., 2015; Bertol et al., 2017), where nutrient losses depend on element concentration and amount of eroded soil. Moreover, selectivity in the erosive process with transport of colloidal particles enriched in nutrients must also be considered (Mendonça et al., 2015; Bertol et al., 2017). High intensity rainfall at periods coinciding with soil tillage with plowing and fertilizer application may strongly increase the transfer of P to surface-water bodies, increasing the potential of eutrophication (Benham et al., 2007; Kerr et al., 2011; Tiecher et al., 2017b). Additionally, in this environment, the main source supplying sediments to the river network are unpawed roads (Minella et al., 2007) and often tobacco cropfields (Tiecher et al., 2017a), and this is precisely the most enriched source in labile and moderately labile P (Tiecher et al., 2019). Soil conservation practices for erosion and runoff control are known. They include management systems with reduction in tillage intensity and maintenance of residues on the soil surface (Minella et al., 2009; Bertol et al., 2017; Reichert et al., 2019), maintaining or increasing soil organic matter (Reichert et al., 2009 and reducing soil compaction (Fullen, 1985) caused by traffic of farm machinery. In a plot-scale, reduction in runoff and suspended solids losses at the edgeof-field was observed in strip- and no-till treatments compared to conventional-till in a burley tobacco production system (Benham et al., 2007). However, there are practically no studies on soil tillage and soil and water erosion/conservation for tobacco cultivation on shallow soils in sloping landscapes. Our hypothesis is that conservation systems for tobacco cultivation provide increased soil cover and protection against erosion processes, reducing losses of water, soil and nutrients compared to traditional farming systems or with some level of soil tillage. The objective was to test soil tillage/management systems capable of reducing soil, water and nutrient losses, as alternatives to conventional tillage and ridges without mulch, in steeplands with shallow soil.
2.1. Study area The study was conducted on a small farm (29°29.55′ S, 53°15,18′ W) in the state of Rio Grande do Sul, southern Brazil. Before the experiment, the study area was cultivated for eight years with tobacco from August to January, and maize from January to May, without the use cover crops (fallow) during the winter period from April to July. The area was cultivated following slope contour lines. Typical tobacco yield in this region ranges from 2.5 to 3.5 Mg ha−1. Soil management operations during this period included tillage, ridging, and grounding in the initial stages of tobacco crop growth. The relief is strongly undulating to steep, with altitudes between 120 and 480 m, predominantly with shallow soils (Dalmolin et al., 2003). Climate is humid subtropical without drought, with average temperature of the hottest month exceeding 22 °C and the temperature of the coldest month varying between −3 and 18 °C (Álvares et al., 2013). Rainfall is usually well distributed, varying from 1300 to 1800 mm year−1 (Maluf, 2000), with higher erosivity in September/ October (Ramon et al., 2016). The experiment was carried out from April 2004 to February 2005 in experimental units allocated to a “Neossolo Litólico Eutrófico típico” (according to the Brazilian Soil Classification System - Dalmolin et al., 2003) or Leptosol (according to the World Reference Base for Soil Resources - IUSS Working Group WRB, 2014), with an average soil depth of 30–40 cm. The physicochemical properties of the Ap horizon (0–20 cm depth) before the establishment of the experiment in April 2004 (before black oats sowing) is presented in Table 1. 2.2. Experimental units and tillage/management systems The experimental area had a total area of about 2700 m2 with homogeneous soil type and slope. The experimental plots had a total area of 150 m2 (10 × 15 m) that were distributed in a randomized blocks design, with three replications and six tillage/management systems. Blocks were separated by a distance of 3 m. Within each experimental unit was allocated the galvanized sheets of 1.0 × 1.2 m (Fig. 1) used to measure water, soil and nutrient losses. In the experimental site, the mean slope of the local landscape was 23% and of the cultivation lines was 2%. The ridges/cultivation lines had 2% slope as used by most farmers in the region to avoid the accumulation of water that can increase the incidence of some diseases in tobacco. The six treatments (Fig. 2) consisted of combinations of winter cover crop management (fallow or black oat cultivation - Avena strigosa Schieb), ridging (without and with ridge), and grounding of the tobacco seedlings (without and with grounding). Table 2 summarizes the combination of these effects used for each treatment. The choice of Table 1 Physicochemical properties of the Ap horizon of the experimental area (0–20 cm depth) in April 2004 before black oats sowing. Soil property
Value −1
Pebbles (g kg ) Gravel (g kg−1) Sand (g kg−1) Silt (g kg−1) Clay (g kg−1) Soil organic matter (g kg−1) Soil pH Available P (mg kg−1) Available K (mg kg−1) Exchangeable Al (cmolc kg−1) Exchangeable Ca (cmolc kg−1) Exchangeable Mg (cmolc kg−1)
2
80 257 482 359 119 11.5 5.2 76 409 0.6 27.2 6.2
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Fig. 1. Slope area and slope of ridges with the position of the galvanized sheets within the plots (a), photography of the galvanized sheets (b) used for runoff and soil collection during rainfall events and animal-driven plowing in the tobacco fields (c, d).
Fig. 2. Tobacco crop at 30 days after transplantation under conventional tillage (CT), minimum tillage after fallow (MTf), minimum tillage after oat (MTo), no-tillage with ridge (NTr), no-tillage with consolidated ridge (NTrc), and no-tillage without ridge (NT). 3
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October Yes Yes – – – – August Together with ridge prepare Together with ridge prepare Together with ridge prepare In a groove 10 cm depth In a groove 10 cm depth In a groove 10 cm depth Plowing in August Plowing in August Plowing in August Plowing in April Ridge of the previous year –
combination of these factors was made according to the main tobacco farming systems used by local farmers. Tillage and ridging operations were done with a reversible moldboard plow, whereas harrowing was performed with triangular spiketooth harrow, all oxen-driven. The ridges were allocated transversely to the terrain slope, with a slope of 2% for water drainage. One day before tobacco transplanting, a groove was opened in the pre-transplant ridge tillage systems (CT, MTf and MTo) for fertilizer application with a manual distributor and then covered with soil displaced from another furrow. For the no-tillage treatments, a plow was used to open a groove in which fertilizer was applied and later incorporated with a second plowing; thus, the fertilizer was closer to the surface than in the tilled treatments. 2.3. Tobacco cropping Virginia-type tobacco seedlings were produced in polystyrene trays with substrate and kept in a mini-greenhouse, in the float system for tobacco transplants. Seedlings were submitted to leaf shedding, which consists of removing the leaf tips when reaching 4 to 6 leaves for stem thickening and improving transplants survival in the field. Seedlings were transplanted in field on 12th September 2004, with spacing of 1.2 m between lines and 0.45–0.50 m between plants, reaching a final population ranging from 16 to 18 thousand plants per hectare. Planting was performed with a manual planter requiring one person to place the seedlings, and another to operate the planter. The management of the spontaneous or black oat residue before the tobacco transplant was performed according to the treatments description in Table 2. Tobacco crop fertilization was based on the amount recommended by the tobacco industry: 850 kg ha−1 of 10-18-20 (NPK) as pre-plant fertilization (base dressing), and two side dressing fertilization with saltpeter of Chile (15-00-14), at 40 and 68 days after transplanting, corresponding to 135 and 126 kg ha−1 of N and K, with a manual equipment locally called as “saraquá”, applied near the crop and at 5cm depth and later grounding. Technical recommendations for tobacco crop management and protection were used. Removal of tobacco flowers (topping) and pruning out unproductive leaves (suckering) were done manually. Leaves were cropped as they ripened, from the bottom to the top of the stalk.
April–July Fallow Fallow Black oats Black oats Black oats Black oats CT MTf MTo NTr NTrc NT Period Conventional tillage Minimum tillage after fallow Minimum tillage after black-oats No-tillage with ridge No-tillage with consolidated ridge No-tillage without ridge
April – – Plowing + harrowing Plowing + harrowing + ridgeprepare – Plowing + harrowing
August Plowing + harrowing – – – – –
Grounding Pre-transplant fertilization Ridge prepare Soil prepare before tobacco transplanting Soil use in winter Soil prepare before winter Symbol Treatments
Table 2 Summary of management adopted in each treatment combining winter cover crop management (fallow or black oat cultivation - Avena strigosa Schieb), ridging (without and with ridge), and grounding of the tobacco seedlings (without and with grounding).
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2.4. Soil cover, water erosion, and nutrient losses The dry mass of the winter plants was evaluated on August 23th 2004, before the transplant of tobacco. Dry mass production of tobacco stems was evaluated on January 18th, 2005. In both evaluations, an area of 1,0 m2 was evaluated, and the sampled material was dried in a forced air circulation oven until reaching constant weight (~72 h). The percentage of soil surface cover was quantified 40 days after tobacco transplanting, discriminating soil covered by rocks and crop residues of winter plants and tobacco crop, in each plot in an area adjacent to the galvanized sheets used to measure water and soil losses. These evaluations were performed perpendicular to the ridges, in two replicates per plot, spaced at 0.1 m, using the linear transect method (Sloneker and Moldenhauer, 1997). Rainfall was monitored throughout the tobacco crop cycle, in a meteorological station distant 500 m from the experiment. Water erosion during rainfall events was evaluated in microplots, by quantifying soil, water, and soluble and total phosphorus and potassium losses. The 1.2-m wide and 1-m long (1.2 m2) microplots were set on ridges with a slope of 2% and delimited with galvanized plates, and water and eroded sediment collected in containers. While certainly playing an important role on soil translocation and even landscape transformation, we did not measure tillage erosion. After each of the eight storm rainfall events occurring during the tobacco cycle, the volume of surface runoff stored in the containers for each storm rainfall was quantified with a 4
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Table 3 Duration, total rainfall, and mean intensity of monitored rainfall events. Rainfall event
Duration
September 20, 2004 September 21, 2004 September 22, 2004 October 13, 2004 October 17, 2004 November 03, 2004 November 05, 2004 December 07, 2004
13 h 5h 9h 5h 12 h 4h 4h 5h
Total rainfall (mm)
20 min 30 min 40 min 00 min 00 min 10 min 00 min 40 min
Mean intensity (mm h−1) 39 9 27 32 75 22 25 24
4.05 1.64 3.04 5.38 5.32 4.99 5.63 5.12
Fig. 3. Exposed soil and cover by mulch, stones and crop at 40 days after transplanting, for soil under conventional tillage (CT), minimum tillage after fallow (MTf), minimum tillage after oat (MTo), no-tillage with ridge (NTr), notillage with consolidated ridge (NTrc), and no-tillage without ridge (NT). Means followed by the same letter comparing exposed soil and cover by mulch, stones and crop do not differ between the treatments (LSD, α = 0.05).
graduated cylinder. It is important to note that although rainfall is well distributed historically throughout the year, rainfall in this region is characterized by rainstorms. Therefore, three rainfall events that occurred on three subsequent days in this study were independently sampled (September 21, 22 and 23, 2004). Duration, total rainfall, and mean intensity of monitored rainfall events are presented in Table 3. Subsequently, homogenized samples of water plus sediment were collected into two subsamples for laboratory analyses. These samples were stored in thermal boxes and taken to the laboratory shortly after each storm rainfall for soluble and total P and K analysis. Soil loss was estimated after drying at 105 °C. Soluble P and K contents were determined after filtration on a cellulose membrane with < 0.45 μm pore-diameter. In the filtrate, P concentration was determined in a UV–Vis spectrophotometer by Murphy and Riley (1962) method and soluble K in a flame emission spectrophotometer. Total P and K were determined after acid digestion (H2SO4 + H2O2) of 20 mL of water + sediment sample in the presence of saturated MgCl2 (Brookes and Powlson, 1981), then, using the amount of soil loss, the concentration of P and K in mg kg−1 were calculated.
tillage system, the minimum cultivation system with moldboard plow (MTo) decreased the percentage of soil cover by black oat residues (Fig. 3) and, thus, increased water loss in four of the eight monitored rainfall-events (September 22, October 13 and 17, and December 07, Fig. 4), and soil loss for five rainfall-events (September 22, 23 and 24, October 17, and November 05, Fig. 5). A large variability in runoff water losses (Fig. 4b) and runoff coefficient (Fig. 4c) was observed in the monitored storm rainfall events, which can be partially attributed to the total volume of rainfall (Fig. 4a). The same was also observed for soil loss (Fig. 5b), soluble and total P (Fig. 6b, c) and K (Fig. 7b, c). In spite of the great temporal variability of the soil loss results (Fig. 5), the sum of the soil losses during the eight monitored storm rainfall (Fig. 8b) shows that there were three main groups: (i) with soil losses ranging between 15 and 16 Mg ha−1 for those treatments without winter cover crops (CT and MTf), (ii) with soil losses ranging between 1.7 and 5.4 Mg ha−1 in those treatments grown with black oats in winter and with ridge, and (iii) the NT treatment, with total soil loss of only 0.2 Mg ha−1. On the other hand, the sum of water runoff losses was only possible in NT treatment (Fig. 8a). Although these differences between treatments are very clear, it is important to note that the monitoring covers a relatively short period (1 season) based on natural rainfall, which generated few events. Moreover, the spatial scale (1.2 m2) where losses were measured is a source of uncertainty. Ridge height and slope, slope of cultivation line and stone cover, among others, can also affect the results. Soluble P content in the runoff water was influenced by the tillage/ management systems in only two events (17th October 2004 and 5th November 2004 – Fig. 6b). The largest and smallest losses occurred, respectively, in the soil under no-tillage system with (NTrc and NTr) and without ridge (NT) construction (Fig. 6b). On the other hand, soluble K concentration in the runoff water was higher in NTr in two rainfall events compared to the other treatments (22th September and
2.5. Statistical analysis Data of plant dry-mass, degree of soil cover, soil and water losses, and losses of soluble and total P and K were submitted to analysis of variance at 5% probability of error and, subsequently, mean were compared using the Least Square Difference (LSD; α = 0.05). 3. Results Winter cover crop (black oats) prior to tobacco transplanting provided two to three times more dry-matter than soil under winter fallow. The amount of tobacco stems dry-matter left prior to the installation of the experiment was small (< 1.6 Mg ha−1), allowing for soil exposure to erosion processes (Table 4). Soil cover provided by tobacco plants was limited to < 25% of the soil surface, not differing between tillage/ management systems. Soil tillage for ridge construction in winterfallow soil (CT and MTf) exposed more than 60% of the soil surface, even 40 days after the transplanting of the seedlings. Compared to no-
Table 4 Dry mass of the cover plants and tobacco stems in different soil tillage/management systems. Tillage/management system
Winter soil cover
Winter plants (23th August 2004)
Tobacco stems (18th January 2005)
Mg ha−1 Conventional tillage (CT) Minimum tillage after fallow (MTf) Minimum tillage after oat (MTo) No-tillage with ridge (NTr) No-tillage with consolidated ridge (NTrc) No-tillage without ridge (NT)
Spontaneous Spontaneous Black oats Black oats Black oats Black oats
2.18c 2.23c 5.32ab 5.47ab 6.60a 4.90b
Means followed by the same letter do not differ (Least Square Difference, LSD; α = 0.05). 5
1.39abc 1.44abc 1.50ab 1.57a 1.31bc 1.25c
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Fig. 4. Rainfall (a), water losses (b) and runoff coefficient (c) in different rainfall events along the tobacco crop cycle, for soil under conventional tillage (CT), minimum tillage after fallow (MTf), minimum tillage after oat (MTo), no-tillage with ridge (NTr), no-tillage with consolidated ridge (NTrc), and no-tillage without ridge (NT). Means followed by the same letter do not differ (LSD, α = 0.05).
17th October 2004 – Fig. 7b). Total P (Fig. 6c) and K (Fig. 7c) concentration in the soil lost differed significantly among tillage/management systems in most rainfall events. There were higher concentrations of total P in sediments from the no-tillage system with ridge (NTrc and NTr). On the other hand, total P content in the soil lost from NT without ridge (NT) was the lowest in the four last rainfall events. By contrast, the highest total K concentration in sediments was observed in no-tilled treatments (NTcr, NTc, and NT), especially in the first three monitored rainfalls (Fig. 7c). By integrating the amount of soil lost transferred with the concentrations of P and K present in the sediment, the amount of these nutrients lost per unit area is obtained (Figs. 6d and 7d). As a consequence of the high soil losses due to soil tillage (CT) or winter fallow followed by ridging immediately before tobacco transplanting (MTf), the amount of P and K leaving the tobacco field-plots are much higher
compared to soil with proper winter cover combined with no-tillage system for tobacco cultivation (MTo, NTrc, NTr and NT). The sum of total P and K losses during the monitored storm rainfall events was 23 and 29 kg ha−1, respectively, in the treatments with winter fallow, ridge and grounding (CT and MTf – Fig. 8d). These losses were reduced about four times when growing black oats in the winter. But only NT without ridge was able to reduce 97 and 57 times the losses of P and K compared to CT. 4. Discussion 4.1. Crop treatment and soil cover The greatest losses of soil and water and the greatest values of runoff coefficient and soil loss occurred in conventional tillage and 6
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Fig. 5. Rainfall (a) and soil loss (b) in different rainfall events along the tobacco crop cycle, for soil under conventional tillage (CT), minimum tillage after fallow (MTf), minimum tillage after oat (MTo), no-tillage with ridge (NTr), no-tillage with consolidated ridge (NTrc), and no-tillage without ridge (NT). Means followed by the same letter do not differ (LSD, α = 0.05).
(Table 4). Throughout the crop cycle under no-tillage system, mulching loses its efficiency mainly because of the transit for crop treatments and leave harvest, while in the conventional plantation the increase of canopy cover by the tobacco plant is not sufficient to reduce soil and water losses (Antoneli and Thomaz, 2014). The no-tillage system alone clearly reduced erosion processes compared to conventional tillage. However, the reduction of soil losses can be potentiated when no-tillage is combined with the use of ridge from the previous year (NTrc) or without the use of ridges (NT). This ratifies that soil management aiming to reduce soil losses should use a combination of conservationist soil management practices, not just one practice, as also demonstrated by Merten et al. (2015). Tobacco-farming watersheds are hydrogeomorphologically impacted because of very-high transfer of soil (Merten and Minella, 2006), nutrients (Pellegrini et al., 2010) and agrochemical molecules to water bodies (Bortoluzzi et al., 2007; Sequinatto et al., 2013), including substances causing metabolic changes in fish (Becker et al., 2009). Furthermore, these farms are located in poor regions with food insecurity, intense deforestation, and high degree of pesticide-intoxicated people (Lecours et al., 2012).
minimum tillage with winter fallow because of intense soil tillage and low vegetation cover, with significant soil exposure to erosion processes. Lower soil and water losses and the lower runoff coefficient were due to the adoption of no-tillage system, regardless of the presence of ridge, natural soil consolidation and oats mulch. In the soil previously cultivated to black oats, minimum soil tillage for ridging show intermediate behavior between total soil inversion with intense tillage and no-tillage system. Tobacco plants produce a low amount of dry-matter since the crop has been genetically improved to combine leaves quantity and quality. In the case of Virginia-type tobacco, the leaves are harvested as they reach physiological maturity and, therefore, only the stems remain on the soil surface at the end of the crop-cycle. The amount of biomass remaining on the soil surface is extremely small and, even worse, stems provide negligible soil cover. Moreover, the amount of root biomass is also very small and is restricted to the ridge, distant 1.2 m from each other. The conventional tobacco production system, therefore, leaves the soil exposed to raindrop impact and overland water flow during the period from the first tillage until the ridging operation, along with a long period until the crop leaves contribute to soil cover. Later, when leave-harvesting begins, soil cover again decreases until exposing 100% of the soil surface. Cover crops during the winter period, such as black oats, on soils with very high nutrient contents will produce, as in the present experiment, a significant amount of biomass. In addition to protecting the soil during the period prior to tobacco transplantation, if no-tillage system or early ridge construction (MT) is adopted, soil cover during the growing stage of the commercial crop is guaranteed. In our study, the degree of soil cover was directly related to the dry-mass produced by the cultivated or spontaneous winter plants and in greater intensity with soil tillage. High soil exposure was mainly due to soil tillage after tobacco transplant, even though the amount of residue produced black oats in the winter was similar for the treatments MTo, NTrc, NTr and NT
4.2. Impact of soil management/tillage on water and soil losses Sediment yield in head-waters catchments under tobacco cultivation was 1.2 (Bonumá et al., 2014) to 3.0 (Antoneli and Thomaz, 2010) times greater in the crop harvesting phase (a 5-months period) compared to tobacco crop off-season, reflecting the intensive tillage and low surface cover of the soil. Under rainfall-simulation in a plot-scale, reduced runoff and total mass of suspended solids losses at the edge-offield were observed in strip- and no-till treatments compared to conventional-till in burley tobacco production system (Benham et al., 2007). The total soil loss on small runoff plots during the eight-storm rainfall monitored during tobacco crop cycle was 78 times greater in 7
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Fig. 6. Rainfall (a), soluble phosphorus losses (b), phosphorus concentration in the soil lost (c), and total phosphorus losses per area (d), for soil under conventional tillage (CT) management systems, minimum tillage after fallow (MTf), minimum tillage after oat (MTo), no-tillage with ridge (NTr), no-tillage with consolidated ridge (NTrc), and no-tillage without ridge (NT). Means followed by the same letter do not differ (LSD, α = 0.05).
CT and NT treatments in our study, there are differences of 1.6-fold, close to the 2-fold observed by Antoneli and Thomaz (2014). While no estimates are available in Brazil for soil losses from tobacco fields, in the USA these losses far exceed the state and national averages as well as soil loss tolerances (Wood and Worsham, 1986). The tolerance of 2.5 Mg ha−1 yr−1 is the lower limit presented by FAO (1967) for shallow soils, which more than 60% of this value was reach in only eight measured rainfall events during five months of monitoring of water, soil and nutrient losses during the tobacco cycle.
conventional-tilled (CT) tobacco than no-till (NT) tobacco, respectively the worst and the best management system for soil and water conservation. These losses are higher than those observed by Wood and Worsham (1986), namely 20 times greater on a sandy loam Aquic Hapludult with 1.3% slope, and lower that those observed by the authors of 90 times greater on a loamy sand Aquic Paleudults with 3.1% slope when comparing these two systems. Losses observed in our study are higher than the ~6-fold observed by Antoneli and Thomaz (2014) in shallow soil using animal traction. When comparing water losses in 8
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Fig. 7. Rainfall (a), soluble potassium losses (b), potassium concentration in the soil lost (c), and total potassium losses per area (d), for soil under conventional tillage (CT) management systems, minimum tillage after fallow (MTf), minimum tillage after oat (MTo), no-tillage with ridge (NTr), no-tillage with consolidated ridge (NTrc), and no-tillage without ridge (NT). Means followed by the same letter do not differ (LSD, α = 0.05).
were the responsible for high soil loss on 13 and 17 October 2004, where the runoff coefficient may explain the higher soil losses even with less total precipitation. On the other hand, the soil losses monitored during the rainfall-events on 03 and 05 November 2004 were very similar as a result of rainfall volume and runoff coefficient.
Soil losses varied with rainfall amount (e.g. rainfall-events monitored on September 21, 22 and 23, 2004), but mainly due to increase in soil antecedent moisture, with rise in the runoff coefficient. Even with less rain, there was an increase in soil losses during the rainfall-events occurred on 22 and 23 September 2004. Rainfall intensity and amount 9
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Fig. 8. Total losses of water (a), soil (b), soluble P and K (c) and total P and K (d) during the monitored rainfall-events events for soil under conventional tillage (CT) management systems, minimum tillage after fallow (MTf), minimum tillage after oat (MTo), no-tillage with ridge (NTr), no-tillage with consolidated ridge (NTrc), and no-tillage without ridge (NT). Means followed by the same letter do not differ (LSD, α = 0.05).
4.3. Impact of soil management/tillage on P and K losses
Initial or antecedent soil moisture is the dominant factor for infiltration and runoff, while rainfall intensity is the dominant factor influencing splash erosion and sediment outflow (Darvishan et al., 2015), and is responsible for most of the runoff in wet soil conditions (MolinaSanchis et al., 2016). As soil erosion processes are also dependent on runoff regardless of land use, Wei et al. (2007) observed that soil loss was more closely correlated to runoff than to rainfall. The largest amounts of runoff and soil loss were recorded in the soil water surplus phase, and the runoff coefficient was exponentially correlated to the inverse of antecedent soil water potential in the rainy season (Wei et al., 2007). In a parallel study, Reichert et al. (2019) observed tillage and ridging for tobacco cropping in the shallow soil reduced the effect of some soil physical stressors to tobacco growth and development. Furthermore, soil management systems with winter cover crop, ridging and reduced soil tillage increased flue-cured tobacco yield, cropped on shallow soils on steeplands. Increased biomass (roots and stalks) production is essential for soil quality and for water infiltration increase and runoff reduction. Finally, although not measured in our study, it is important to recognized the occurrence of tillage erosion on the studied site. The particular implement characteristics cause high spatial variability in soil redistribution patterns (De Alba et al., 2006), but generally soil loss occurs on convex areas and deposition takes place on concave areas. Loss of soil mass generates soil profile truncation on convexities and in upper areas of the cultivated hillslopes; while in concavities and lower areas of the field the opposite effect occurs, burying the original soil profile (De Alba et al., 2004). Rates of tillage soil translocation are proportional to slope gradient, while net rates of soil loss or gain are related to morphology and slope curvature (Lindstrom et al., 1992; Govers et al., 1994).
Ridging before transplanting or ridge maintenance for more than one cropping season, a premise of the no-tillage system, may induce greater losses of soluble nutrients, because of the difficulty of ‘injecting’ fertilizers into soil ridge. In contrast, losses of soluble K and P were low when fertilizers were added into the ridge in tilled soil in the CT, MTf and MTo treatments. Thus, the combination of no-tillage management, fertilizer application on the ridge, and the occurrence of rainfall soon after transplanting resulted in large bioavailable-nutrients transfer to aquatic bodies. The levels of soluble elements in the runoff water can be tens and even hundreds of times greater than those observed in waters draining non-anthropogenic areas (Pellegrini et al., 2010; Kaiser et al., 2015). In our study, soluble K contents reached 5 mg L−1 in soil with partial or total inversion during tillage (CT, MTf and MTo) and fertilization on the ridge, compared to values lower than 2.0 mg L−1 in the drainage network of our studied watershed during the period from January to August 2002 observed by Gonçalves et al. (2005). The quantities and forms of P and K transferred vary between rainfall events, because of variations in intensity and duration, time interval between rains, degree of soil cover (Sharpley et al., 1992), degree of saturation of soil colloids by the chemical element and fertilizer dose and time of application. Losses per unit area of P and K bound to sediments were dependent on the amount of soil lost. This is due to the high cation exchange capacity of the studied soil (Table 1), which contributes to the retention of K, and the high adsorption capacity of P due to the presence of Fe oxides in the clay fraction. When this soil reaches the water bodies, the amounts of P and K desorbed from the sediments to the water column may be much larger than the amount of elements desorbed in the soil from where it is originated as shown by Bortoluzzi et al. (2013). Water contamination by phosphates in watershed is facilitated by erosion processes and traditional tobacco cropping system due to high sediment concentration and low organic 10
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carbon (Pellegrini et al., 2010). Sediment concentration and quality are related to fertilization and selectivity of erosion, where the finest and richest soil fraction is selectively transported (Mendonça et al., 2015; Bertol et al., 2017). These losses were minimized with the increase of soil cover and decrease in tillage, because the magnitude of nutrient losses was associated with the amount of soil lost. As a consequence, the reduction in the productive capacity of the soil will occur in the medium and long term, requiring greater fertilizer applications to compensate the losses. It is important to note that the losses of P and K evaluated in the present study are only related to losses due to surface runoff. An important component is losses by leaching, especially in shallow soils with high bioavailable P and K content as in the present study (Table 1) that has not been evaluated and should be taken into account in future studies. In some cases, depending on the soil depth, the application of fertilizers directly into the ridges can even increase the potential for leaching losses and should be avoided.
systems in Southwest Virginia. Water Air Soil Poll 179, 159–166. https://doi.org/10. 1007/s11270-006-9221-z. Bertol, I., Luciano, R.V., Bertol, C., Bagio, B., 2017. Nutrient and organic carbon losses, enrichment rate, and cost of water erosion. Rev. Bras. Cienc. Solo 41, e0160150. https://doi.org/10.1590/18069657rbcs20160150. Bonumá, N.B., Rossi, C.G., Arnold, J.G., Reichert, J.M., Minella, J.P.G., Allen, P.M., Volk, M., 2014. Simulating landscape sediment transport capacity by using a modified SWAT model. J. Environ. Qual. 43, 55–66. https://doi.org/10.2134/jeq2012.0217. Bortoluzzi, E.C., Rheinheimer, D.S., Gonçalves, C.S., Pellegrini, J.B.R., Maroneze, A.M., Kurz, M.H.S., Bacar, N.M., Zanella, R., 2007. Investigation of the occurrence of pesticide residues in rural wells and surface water following application to tobacco. Quim Nova 30, 1872–1876. https://doi.org/10.1590/S0100-40422007000800014. Bortoluzzi, E.C., Rheinheimer, D.S., Santanna, M.A., Caner, L., 2013. Mineralogy and nutrient desorption of suspended sediments during a storm event. J Soil Sedim 13, 1093–1105. https://doi.org/10.1007/s11368-013-0692-4. Brookes, P.C., Powlson, D.C., 1981. Preventing phosphorus losses during perchloric acid digestion of sodium bicarbonate soil extracts. J. Sci. Food Agr. 32, 671–674. https:// doi.org/10.1002/jsfa.2740320707. Dalmolin, R.S.D., Pedron, F.A., Azevedo, A.C., Zago, A., 2003. Levantamento semidetalhado de solos da microbacia do arroio Lino – município de Agudo (RS). 2003 (84p). Darvishan, A.K., Banasik, K., Sadeghi, S.H., Gholami, L., Hejduk, L., 2015. Effects of rain intensity and initial soil moisture on hydrological responses in laboratory conditions. Int. Agrophys. 29, 165–173. https://doi.org/10.1515/intag-2015-0020. De Alba, S., Lindstrom, M., Schumacher, T.E., Malo, D.D., 2004. Soil landscape evolution due to soil redistribution by tillage: a new conceptual model of soil catena evolution in agricultural landscapes. Catena 58, 77–100. https://doi.org/10.1016/j.catena. 2003.12.004. De Alba, S., Borselli, L., Torri, D., Pellegrini, S., Bazzoffi, P., 2006. Assessment of tillage erosion by mouldboard plough in Tuscany (Italy). Soil Tillage Res. 85, 123–142. https://doi.org/10.1016/j.still.2004.12.002. FAO - Food and Agriculture Organization of the United Nations, 1967. La erosión del suelo por el agua: Algunas medidas para combatirla en las tierras de cultivo. Organización de las Naciones Unidas, Roma (207p). Fullen, M.A., 1985. Compaction, hydrological processes and soil erosion on loamy sands in east Shropshire, England. Soil Till. Res. 6, 17–29.. https://doi.org/10.1016/01671987(85)90003-0. Gonçalves, C.S., Rheinheimer, D.S., Pellegrini, J.B.R., Kist, S.L., 2005. Qualidade da água numa microbacia hidrográfica de cabeceira situada em região produtora de fumo. Rev. Bras. Eng. Agric. Ambient. 9, 391–399. https://doi.org/10.1590/S141543662005000300015. Govers, G., Vandaele, K., Desmet, P.J.J., Poesen, J., Bunte, K., 1994. The role of tillage in soil redistribution on hillslopes. Eur. J. Soil Sci. 45, 469–478. https://doi.org/10. 1111/j.1365-2389.1994.tb00532.x. IUSS Working Group WRB, 2014. World Reference Base for Soil Resources 2014. International Soil Classification System for Naming Soils and Creating Legends for Soil Maps. FAO, Rome, Italy, pp. 203. Kaiser, D.R., Reinert, D.J., Reichert, J.M., Streck, C.A., Pellegrini, A., 2010. Nitrate and ammonium in soil solution in tobacco management systems. Rev. Bras. Cienc. Solo 34, 379–388. https://doi.org/10.1590/S0100-06832010000200011. Kaiser, D.R., Sequinatto, L., Reinert, D.J., Reichert, J.M., Rheinheimer, D.S., Dalbianco, L., 2015. High nitrogen fertilization of tobacco crop in headwater watershed contaminates subsurface and well waters with nitrate. J. Chem. 1–11. https://doi.org/ 10.1155/2015/375092. Kerr, J.G., Burford, M.A., Olley, J.M., Bunn, S.E., Udy, J., 2011. Examining the link between terrestrial and aquatic phosphorus speciation in a subtropical catchment: the role of selective erosion and transport of fine sediments during storm events. Water Res.Water Res 45, 3331–3340. https://doi.org/10.1016/j.watres.2011.03.048. Lecours, N., Almeida, G.E.G., Abdallah, J.M., Novotny, T.E., 2012. Environmental health impacts of tobacco farming: a review of the literature. Tob. Control.Tob. Control 21, 191–196. https://doi.org/10.1136/tobaccocontrol-2011-050318. Maluf, J.R.T., 2000. Nova classificação climática do Estado do Rio Grande do Sul. Rev. Bras. Agrometeorol. 8, 141–150. Mendonça, P.G., Silva Júnior, J.F., Oliveira, I.R., Teixeira, D.B., Moitinho, M.R., Martins Filho, M.V., Marques Júnior, J., Pereira, G.T., 2015. Spatial uncertainty of nutrient loss by erosion in sugarcane harvesting scenarios. Rev. Bras. Cienc. Solo 39, 1181–1189. https://doi.org/10.1590/01000683rbcs20140432. Merten, G.H., Minella, J.P.G., 2006. Impact on sediment yield caused by intensification of tobacco production in a catchment in southern Brazil. Cienc. Rural 36, 669–672. https://doi.org/10.1590/S0103-84782006000200050. Merten, G.H., Araújo, A.G., Biscaia, R.C.M., Barbosa, G.M.C., Conte, O., 2015. No-till surface runoff and soil losses in southern Brazil. Soil. Till. Res. 152, 85–93. https:// doi.org/10.1016/j.still.2015.03.014. Minella, J.P.G., Merten, G.H., Reichert, J.M., Santos, D.R., 2007. Identificação e implicações para a conservação do solo das fontes de sedimentos em bacias hidrográficas. Rev. Bras. Cienc. Solo 31, 1637–1646. https://doi.org/10.1590/ S0100-06832007000600039. Minella, J.P.G., Merten, G.H., Walling, D.E., Reichert, J.M., 2009. Changing sediment yield as an indicator of improved soil management practices in southern Brazil. Catena 79, 228–236. https://doi.org/10.1016/j.catena.2009.02.020. Molina-Sanchis, I., Lázaro, R., Arnau-Rosalén, E., Calvo-Cases, A., 2016. Rainfall timing and runoff: the influence of the criterion for rain event separation. J. Hydrol. Hydromech. 64 (63), 226–236. https://doi.org/10.1515/johh-2016-0024. Murphy, J., Riley, J.P., 1962. A modified single solution method for the determination of phosphate in natural waters. Anal. Chim. Acta 27, 31–36. https://doi.org/10.1016/ S0003-2670(00)88444-5.
5. Conclusion The widespread use of intense soil tillage and the ridging before tobacco transplanting and for grounding of growing plants favor soil degradation and the increase in soil, water and nutrient losses, which are aggravated by winter fallow. Soil exposure coincides with the rainy season, with higher rainfall volume on high-moisture soil. Conservation tillage/management systems for tobacco cultivation, including the use of winter cover crops such as black oats and minimal soil mobilization for ridge construction and maintenance, are alternatives indicated for tobacco farmers once it resulted in drastic reduction in losses of soil, water, phosphorus and potassium (especially adsorbed to the sediments). However, the addition of fertilizers inside the ridge is mandatory; otherwise it will strongly increase the transfer of bioavailable phosphorus and potassium to surface-water bodies, increasing the potential for eutrophication promoted by phosphorus input, and unnecessarily increasing the costs of production with the replacement of fertilizers. Acknowledgments We thank to CNPq (Brazilian National Council for Scientific and Technological Development) for fellowship for the first and last authors, CAPES (Coordination for the Improvement of Higher Education Personnel) for graduate student scholarships, and FAPERGS (Rio Grande do Sul State Research Foundation) and CNPq for research grant and undergraduate scholarships. References AFUBRA. 2016. Associação dos Fumicultores do Brasil. Fumicultura, 2016. Acesso em: 13/04/2017. Disponível em: < http://www.afubra.com.br > . Alameda, D., Anten, N.P.R., Villar, R., 2012. Soil compaction effects on growth and root traits of tobacco depend on light, water regime and mechanical stress. Soil Tillage Res. 120, 121–129. https://doi.org/10.1016/j.still.2011.11.013. Álvares, C.A., Stape, J.L., Sentelhas, P.C., Goncalves, J.L.M., Sparovek, G., 2013. Koppen’s climate classification map for Brazil. Meteorologische Zeitschrif 22, 711–728. https://doi.org/10.1127/0941-2948/2013/0507. Antoneli, V., Thomaz, E.L., 2010. Relação entre o cultivo de fumo (Nicotiana tabacum) e a produção de sedimentos na Bacia do Arroio Boa Vista, Guamiranga - PR. Geografia 35, 383–398. Antoneli, V., Thomaz, E.L., 2014. Perda de solo em cultivo de tabaco sob diferentes formas de cultivo na região Sudeste do Paraná. Rev. Bras. Geomorfol. 15, 455–469. https://doi.org/10.20502/rbg.v15i3.534. Bagio, B., Bertol, I., Wolschick, N.H., Schneiders, D., Santos, M.A.N., 2017. Water erosion in different slope lengths on bare soil. Rev. Bras. Cienc. Solo 41, e0160132. https:// doi.org/10.1590/18069657rbcs20160132. Becker, A.G., Moraes, B.S., Menezes, C.C., Loro, V.L., Rheinheimer, D.S., Reichert, J.M., Balsisserotto, B., 2009. Pesticide contamination of water alters the metabolism of juvenile silver catfish, Rhamdia quelen. Ecotoxicol. Environ. Saf. 72, 1734–1739. https://doi.org/10.1016/j.ecoenv.2009.01.006. Benham, B.L., Vaughan, D.H., Laird, M.K., Ross, B.B., Peek, D.R., 2007. Surface water quality impacts of conservation tillage practices on burley tobacco production
11
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J.M. Reichert, et al.
Sequinatto, L., Reichert, J.M., Rheinheimer, D.S., Reinert, D.J., Copetti, A.C.C., 2013. Occurrence of agrochemicals in surface waters of shallow soils and steep slopes cropped to tobacco. Quim NovaQuim. Nova 36, 768–772. 2013. https://doi.org/10. 1590/S0100-40422013000600004. Sharpley, A.N., Smith, S.J., Jones, O.R., 1992. The transport of bioavailable phosphorus in agricultural runoff. J. Environ. Qual. 21, 30–35. https://doi.org/10.2134/jeq1992. 00472425002100010003x. Sloneker, L.L., Moldenhauer, W.C., 1997. Measuring the amounts of crop residue remaining after tillage. J. Soil Water Conserv. 32, 231–236. Tiecher, T., Caner, L., Minella, J.P.G., Evrard, O., Mondamert, L., Labanowski, J., Rheinheimer, D.S., 2017a. Tracing sediment sources using mid-infrared spectroscopy in Arvorezinha catchment, southern Brazil. Land Deg. Dev. 28, 1603–1614. https:// doi.org/10.1002/ldr.2690. Tiecher, T., Schenato, R.B., Santanna, M.A., Caner, L., Rheinheimer, D.S., 2017b. Phosphorus forms in sediments as indicators of anthropic pressures in an agricultural catchment in southern Brazil. Rev. Bras. Cienc. Solo 41, e0160569. https://doi.org/ 10.1590/18069657rbcs20160569. Tiecher, T., Ramon, R., Laceby, J.P., Evrard, O., Minella, J.P.G., 2019. Potential of phosphorus fractions to trace sediment sources in a rural catchment of southern Brazil: comparison with the conventional approach based on elemental geochemistry. Geoderma 337, 1067–1076. https://doi.org/10.1016/j.geoderma.2018.11.011. Turšić, I., Mesić, M., Kisić, I., Racz, A., 2016. Influence of bulk density on soil resistance and yield of tobacco. Int. J. Plant Res. 6, 21–24. https://doi.org/10.5923/j.plant. 20160602.01. Wei, L., Zhang, B., Wang, M., 2007. Effects of antecedent soil moisture on runoff and soil erosion in alley cropping systems. Agr. Water Manage. 94, 54–62. https://doi.org/10. 1016/j.agwat.2007.08.007. Wood, S.D., Worsham, A.D., 1986. Reducing soil erosion in tobacco fields with no-tillage transplanting. J. Soil Water Conserv. 41, 193–196.
Oliveira, F.P., Buarque, D.C., Vieiro, A.C., Merten, G.H., Cassol, E.A., Minella, J.P.G., 2012. Fatores relacionados à suscetibilidade da erosão em entressulcos sob condições de uso e manejo do solo. Rev. Bras. Eng. Agric. Ambient. 16, 337–346. https://doi. org/10.1590/S1415-43662012000400002. Pellegrini, J.B.R., Rheinheimer, D.S., Gonçalves, C.S., Copetti, A.C.C., Bortoluzzi, E.C., Tessier, D., 2010. Impacts of anthropic pressures on soil phosphorus availability, concentration, and phosphorus forms in sediments in a southern Brazilian watershed. J. Soils SedimentsJ. Soil. Sediment. 10, 451–460. https://doi.org/10.1007/s11368009-0125-6. Petry, C., Rheinheimer, D.S., Kaminski, J., Pessoa, A.C.S., Cassol, L.C., 1994. Influência do estresse de alumínio em plantas de fumo: II. Efeito nos parâmetros cinéticos de absorção de fósforo. Rev. Bras. Cienc. Solo 18, 69–72. https://doi.org/10.1590/ S0100-06832000000300007. Ramon, R., Minella, J.P.G., Merten, G.H., Barros, C.A.P., Canale, T., 2016. Kinetic energy estimation by rainfall intensity and its usefulness in predicting hydrosedimentological variables in a small rural catchment in southern Brazil. Catena 148, 176–184. https://doi.org/10.1016/j.catena.2016.07.015. Reichert, J.M., Norton, L.D., Favaretto, N., Huang, C., Blume, E., 2009. Settling velocity, aggregate stability, and interrill erodibility of soils varying in clay mineralogy. Soil Sci. Soc. Am. J. 73, 1369–1377. https://doi.org/10.2136/sssaj2007.0067. Reichert, J.M., Pellegrini, A., Rodrigues, M.F., 2019. Tobacco growth, yield and quality affected by soil constraints on steeplands. Ind. Crop. Prod.Ind. Crops Prod. 128, 512–526. https://doi.org/10.1016/j.indcrop.2018.11.037. Reichert, J.M., Amado, T.J.C., Reinert, D.J., Rodrigues, M.F., Suzuki, L.E.A.S., 2016. Land use effects on subtropical, sandy soil under sandyzation/desertification processes. Agric. Ecosyst. Environ 233, 370–380. https://doi.org/10.1016/j.agee.2016.09.039. Rheinheimer, D.S., Petry, C., Kaminski, J., Bartz, H.R., 1994. Influência do estresse de alumínio em plantas de fumo: I. Efeitos no sistema radicular, na absorção de fósforo e cálcio e no acúmulo de massa seca. Rev. Bras. Cienc. Solo 18, 63–68.
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Impact of tobacco management practices on soil, water and nutrients losses in steeplands with shallow soil
T
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José Miguel Reicherta, , André Pellegrinib, Miriam Fernanda Rodriguesa, Tales Tiecherc, Danilo Rheinheimer dos Santosa a
Department of Soil Science, Universidade Federal de Santa Maria (UFSM), 97105-900 Santa Maria, Rio Grande do Sul State, Brazil Universidade Tecnológica Federal do Paraná, 97105-490 Dois Vizinhos, Paraná State, Brazil c Department of Soil Science, Faculty of Agronomy, Interdisciplinary Research Group on Environmental Biogeochemistry (IRGEB), Universidade Federal do Rio Grande do Sul, 91540-000 Porto Alegre, Rio Grande do Sul State, Brazil b
A R T I C LE I N FO
A B S T R A C T
Keywords: Intensive tillage Conservation practices Erosion Sediment contamination Nutrient loss
Tobacco is produced in Brazil mainly by small farmholders, on shallow soils on steeplands or on sandy soils, usually under intense soil tillage and lacking soil conservation measures, which can result in large losses of water, soil and nutrients such as P and K. We studied soil management systems for tobacco cropped using animal traction, on shallow soil on steeplands. On a Leptosol, we evaluated conventional tillage (CT), minimum tillage after fallow (MTf), minimum tillage after oat (MTo), no-tillage without ridge (NT), no-tillage with ridge (NTr) and no-tillage with consolidated ridge (NTrc), in a completely randomized blocks design with three replicates. Runoff plots of 1.2 m2 were used to determine water and soil loss by runoff, and total and soluble P and K losses in eight rainfall events during the tobacco crop cycle. Oat cultivation prior to tobacco provided higher dry-mass mulch production and the lowest proportion of exposed soil and rocks in NTr, NTrc and NT systems. The losses of water and of P and K in the soluble forms during the storm rainfall events evaluated were lower for NT management compared to the other treatments. Total soil loss for the monitored rainfall-events was 15 and 16 Mg ha−1 for CT and MTf management, and it was reduced about five times for MTo, NTrc and NTr treatments. However, the lowest soil loss was observed for NT (0.2 Mg ha−1). This same trend was observed for total losses of P and K, where NT reduced about 97 and 57 times the losses of these nutrients compared to CT. Therefore, these results show that conservation managements such as no-tillage or minimum tillage associated with winter cover crops without grounding of tobacco seedlings may be effective to reduce soil losses along with P and K adsorbed in the soil. However, reduction of losses of water, soluble and total P and K was only effective combining notillage with no ridge construction and winter cover crop.
1. Introduction Brazil was the world leader in tobacco (Nicotiana tabacum L.) exports in the 2011/2012 agricultural year, and the second place in production with more than 500 thousand tons in 2015/2016. In the three southern States, tobacco farming was the main agricultural activity of approximately 144 thousand families that grow 271 thousand hectares (Afubra, 2016) in an integrated system between familyfarmers and international agro-industries. Tobacco production is mainly carried out in regions with large numbers of families and labor availability in small farming units, in two types of agroecological conditions: (i) sloping areas naturally unsuitable for annual crops, due to the presence of shallow soils (Dalmolin et al.,
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2003) and highly susceptible to erosion (Bonumá et al., 2014), and (ii) sandy soils of low resistance to degradation (Reichert et al., 2016). In both environments, tobacco is cultivated with intense soil tillage and lack of conservation practices in most of the cultivated areas (Merten and Minella, 2006). Leaves are the commercial product of high added-value and have, thus, been the sole focus of tobacco genetic improvement. Tobacco root system has little absorption surface (thick, sparsely branched roots with very few roots - Rheinheimer et al., 1994) and nutrient absorption capacity, especially phosphorus (low maximum inflow of P, and high minimum concentration of P in the solution for absorption - Petry et al., 1994), thus requiring high doses of fertilizers and tillage to loosen the soil. Moreover, tobacco roots are not tolerant to limited-drainage and
Corresponding author. E-mail address: [email protected] (J.M. Reichert).
https://doi.org/10.1016/j.catena.2019.104215 Received 21 March 2019; Received in revised form 12 July 2019; Accepted 5 August 2019 0341-8162/ © 2019 Elsevier B.V. All rights reserved.
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2. Material and methods
compacted soils (Alameda et al., 2012; Turšić et al., 2016). Soil tillage is an essential practice to obtain adequate tobacco yield. Nevertheless, there is a strong contradiction between tilling the whole field and the need for ridge construction, since tobacco root growth between crop rows is reduced. Furthermore, there is intense human, animal or mechanized traffic between crop lines to perform phytosanitary treatments and, particularly, leaves harvesting. The crop does not provide soil coverage along the crop cycle and favors soil exposure to erosive processes. In conventional tillage for tobacco on steeplands, animal-driven plowing moves soil from the top of the field downward. Thus, there is a net soil translocation on the hillslope due to tillage operations, exposing subsoil at the crest while burying soil at the bottom. With tillage erosion no soil has to leave the field, but the effects for productivity and increased yield variability can be significant. The combination of cultivating agroecologically fragile lands, intense soil tillage, high nutrient supply, and roots with inefficient absorption capacity lead to increased tobacco production costs and high environmental contamination. High erosion rates and water contamination with sediments (Merten and Minella, 2006; Minella et al., 2009; Oliveira et al., 2012) and agrochemicals (Pellegrini et al., 2010; Kaiser et al., 2010, 2015) characterize rural watersheds where tobacco is the main cash crop. Erosion and contamination are significant in tobacco cultivation, since the season of soil tillage coincides with high-erosivity rainfall (Ramon et al., 2016). Erosive rains on bare soil cause intense erosion, soil degradation, reduction of productive capacity, high sediment yield, and contamination of water resources (Merten and Minella, 2006; Minella et al., 2009; Bagio et al., 2017; Bertol et al., 2017). Concentration of P and K in runoff varies mainly with its solubility in water and its concentration in soil, which is influenced by fertilization, management, and soil type (Mendonça et al., 2015; Bertol et al., 2017), where nutrient losses depend on element concentration and amount of eroded soil. Moreover, selectivity in the erosive process with transport of colloidal particles enriched in nutrients must also be considered (Mendonça et al., 2015; Bertol et al., 2017). High intensity rainfall at periods coinciding with soil tillage with plowing and fertilizer application may strongly increase the transfer of P to surface-water bodies, increasing the potential of eutrophication (Benham et al., 2007; Kerr et al., 2011; Tiecher et al., 2017b). Additionally, in this environment, the main source supplying sediments to the river network are unpawed roads (Minella et al., 2007) and often tobacco cropfields (Tiecher et al., 2017a), and this is precisely the most enriched source in labile and moderately labile P (Tiecher et al., 2019). Soil conservation practices for erosion and runoff control are known. They include management systems with reduction in tillage intensity and maintenance of residues on the soil surface (Minella et al., 2009; Bertol et al., 2017; Reichert et al., 2019), maintaining or increasing soil organic matter (Reichert et al., 2009 and reducing soil compaction (Fullen, 1985) caused by traffic of farm machinery. In a plot-scale, reduction in runoff and suspended solids losses at the edgeof-field was observed in strip- and no-till treatments compared to conventional-till in a burley tobacco production system (Benham et al., 2007). However, there are practically no studies on soil tillage and soil and water erosion/conservation for tobacco cultivation on shallow soils in sloping landscapes. Our hypothesis is that conservation systems for tobacco cultivation provide increased soil cover and protection against erosion processes, reducing losses of water, soil and nutrients compared to traditional farming systems or with some level of soil tillage. The objective was to test soil tillage/management systems capable of reducing soil, water and nutrient losses, as alternatives to conventional tillage and ridges without mulch, in steeplands with shallow soil.
2.1. Study area The study was conducted on a small farm (29°29.55′ S, 53°15,18′ W) in the state of Rio Grande do Sul, southern Brazil. Before the experiment, the study area was cultivated for eight years with tobacco from August to January, and maize from January to May, without the use cover crops (fallow) during the winter period from April to July. The area was cultivated following slope contour lines. Typical tobacco yield in this region ranges from 2.5 to 3.5 Mg ha−1. Soil management operations during this period included tillage, ridging, and grounding in the initial stages of tobacco crop growth. The relief is strongly undulating to steep, with altitudes between 120 and 480 m, predominantly with shallow soils (Dalmolin et al., 2003). Climate is humid subtropical without drought, with average temperature of the hottest month exceeding 22 °C and the temperature of the coldest month varying between −3 and 18 °C (Álvares et al., 2013). Rainfall is usually well distributed, varying from 1300 to 1800 mm year−1 (Maluf, 2000), with higher erosivity in September/ October (Ramon et al., 2016). The experiment was carried out from April 2004 to February 2005 in experimental units allocated to a “Neossolo Litólico Eutrófico típico” (according to the Brazilian Soil Classification System - Dalmolin et al., 2003) or Leptosol (according to the World Reference Base for Soil Resources - IUSS Working Group WRB, 2014), with an average soil depth of 30–40 cm. The physicochemical properties of the Ap horizon (0–20 cm depth) before the establishment of the experiment in April 2004 (before black oats sowing) is presented in Table 1. 2.2. Experimental units and tillage/management systems The experimental area had a total area of about 2700 m2 with homogeneous soil type and slope. The experimental plots had a total area of 150 m2 (10 × 15 m) that were distributed in a randomized blocks design, with three replications and six tillage/management systems. Blocks were separated by a distance of 3 m. Within each experimental unit was allocated the galvanized sheets of 1.0 × 1.2 m (Fig. 1) used to measure water, soil and nutrient losses. In the experimental site, the mean slope of the local landscape was 23% and of the cultivation lines was 2%. The ridges/cultivation lines had 2% slope as used by most farmers in the region to avoid the accumulation of water that can increase the incidence of some diseases in tobacco. The six treatments (Fig. 2) consisted of combinations of winter cover crop management (fallow or black oat cultivation - Avena strigosa Schieb), ridging (without and with ridge), and grounding of the tobacco seedlings (without and with grounding). Table 2 summarizes the combination of these effects used for each treatment. The choice of Table 1 Physicochemical properties of the Ap horizon of the experimental area (0–20 cm depth) in April 2004 before black oats sowing. Soil property
Value −1
Pebbles (g kg ) Gravel (g kg−1) Sand (g kg−1) Silt (g kg−1) Clay (g kg−1) Soil organic matter (g kg−1) Soil pH Available P (mg kg−1) Available K (mg kg−1) Exchangeable Al (cmolc kg−1) Exchangeable Ca (cmolc kg−1) Exchangeable Mg (cmolc kg−1)
2
80 257 482 359 119 11.5 5.2 76 409 0.6 27.2 6.2
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Fig. 1. Slope area and slope of ridges with the position of the galvanized sheets within the plots (a), photography of the galvanized sheets (b) used for runoff and soil collection during rainfall events and animal-driven plowing in the tobacco fields (c, d).
Fig. 2. Tobacco crop at 30 days after transplantation under conventional tillage (CT), minimum tillage after fallow (MTf), minimum tillage after oat (MTo), no-tillage with ridge (NTr), no-tillage with consolidated ridge (NTrc), and no-tillage without ridge (NT). 3
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October Yes Yes – – – – August Together with ridge prepare Together with ridge prepare Together with ridge prepare In a groove 10 cm depth In a groove 10 cm depth In a groove 10 cm depth Plowing in August Plowing in August Plowing in August Plowing in April Ridge of the previous year –
combination of these factors was made according to the main tobacco farming systems used by local farmers. Tillage and ridging operations were done with a reversible moldboard plow, whereas harrowing was performed with triangular spiketooth harrow, all oxen-driven. The ridges were allocated transversely to the terrain slope, with a slope of 2% for water drainage. One day before tobacco transplanting, a groove was opened in the pre-transplant ridge tillage systems (CT, MTf and MTo) for fertilizer application with a manual distributor and then covered with soil displaced from another furrow. For the no-tillage treatments, a plow was used to open a groove in which fertilizer was applied and later incorporated with a second plowing; thus, the fertilizer was closer to the surface than in the tilled treatments. 2.3. Tobacco cropping Virginia-type tobacco seedlings were produced in polystyrene trays with substrate and kept in a mini-greenhouse, in the float system for tobacco transplants. Seedlings were submitted to leaf shedding, which consists of removing the leaf tips when reaching 4 to 6 leaves for stem thickening and improving transplants survival in the field. Seedlings were transplanted in field on 12th September 2004, with spacing of 1.2 m between lines and 0.45–0.50 m between plants, reaching a final population ranging from 16 to 18 thousand plants per hectare. Planting was performed with a manual planter requiring one person to place the seedlings, and another to operate the planter. The management of the spontaneous or black oat residue before the tobacco transplant was performed according to the treatments description in Table 2. Tobacco crop fertilization was based on the amount recommended by the tobacco industry: 850 kg ha−1 of 10-18-20 (NPK) as pre-plant fertilization (base dressing), and two side dressing fertilization with saltpeter of Chile (15-00-14), at 40 and 68 days after transplanting, corresponding to 135 and 126 kg ha−1 of N and K, with a manual equipment locally called as “saraquá”, applied near the crop and at 5cm depth and later grounding. Technical recommendations for tobacco crop management and protection were used. Removal of tobacco flowers (topping) and pruning out unproductive leaves (suckering) were done manually. Leaves were cropped as they ripened, from the bottom to the top of the stalk.
April–July Fallow Fallow Black oats Black oats Black oats Black oats CT MTf MTo NTr NTrc NT Period Conventional tillage Minimum tillage after fallow Minimum tillage after black-oats No-tillage with ridge No-tillage with consolidated ridge No-tillage without ridge
April – – Plowing + harrowing Plowing + harrowing + ridgeprepare – Plowing + harrowing
August Plowing + harrowing – – – – –
Grounding Pre-transplant fertilization Ridge prepare Soil prepare before tobacco transplanting Soil use in winter Soil prepare before winter Symbol Treatments
Table 2 Summary of management adopted in each treatment combining winter cover crop management (fallow or black oat cultivation - Avena strigosa Schieb), ridging (without and with ridge), and grounding of the tobacco seedlings (without and with grounding).
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2.4. Soil cover, water erosion, and nutrient losses The dry mass of the winter plants was evaluated on August 23th 2004, before the transplant of tobacco. Dry mass production of tobacco stems was evaluated on January 18th, 2005. In both evaluations, an area of 1,0 m2 was evaluated, and the sampled material was dried in a forced air circulation oven until reaching constant weight (~72 h). The percentage of soil surface cover was quantified 40 days after tobacco transplanting, discriminating soil covered by rocks and crop residues of winter plants and tobacco crop, in each plot in an area adjacent to the galvanized sheets used to measure water and soil losses. These evaluations were performed perpendicular to the ridges, in two replicates per plot, spaced at 0.1 m, using the linear transect method (Sloneker and Moldenhauer, 1997). Rainfall was monitored throughout the tobacco crop cycle, in a meteorological station distant 500 m from the experiment. Water erosion during rainfall events was evaluated in microplots, by quantifying soil, water, and soluble and total phosphorus and potassium losses. The 1.2-m wide and 1-m long (1.2 m2) microplots were set on ridges with a slope of 2% and delimited with galvanized plates, and water and eroded sediment collected in containers. While certainly playing an important role on soil translocation and even landscape transformation, we did not measure tillage erosion. After each of the eight storm rainfall events occurring during the tobacco cycle, the volume of surface runoff stored in the containers for each storm rainfall was quantified with a 4
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Table 3 Duration, total rainfall, and mean intensity of monitored rainfall events. Rainfall event
Duration
September 20, 2004 September 21, 2004 September 22, 2004 October 13, 2004 October 17, 2004 November 03, 2004 November 05, 2004 December 07, 2004
13 h 5h 9h 5h 12 h 4h 4h 5h
Total rainfall (mm)
20 min 30 min 40 min 00 min 00 min 10 min 00 min 40 min
Mean intensity (mm h−1) 39 9 27 32 75 22 25 24
4.05 1.64 3.04 5.38 5.32 4.99 5.63 5.12
Fig. 3. Exposed soil and cover by mulch, stones and crop at 40 days after transplanting, for soil under conventional tillage (CT), minimum tillage after fallow (MTf), minimum tillage after oat (MTo), no-tillage with ridge (NTr), notillage with consolidated ridge (NTrc), and no-tillage without ridge (NT). Means followed by the same letter comparing exposed soil and cover by mulch, stones and crop do not differ between the treatments (LSD, α = 0.05).
graduated cylinder. It is important to note that although rainfall is well distributed historically throughout the year, rainfall in this region is characterized by rainstorms. Therefore, three rainfall events that occurred on three subsequent days in this study were independently sampled (September 21, 22 and 23, 2004). Duration, total rainfall, and mean intensity of monitored rainfall events are presented in Table 3. Subsequently, homogenized samples of water plus sediment were collected into two subsamples for laboratory analyses. These samples were stored in thermal boxes and taken to the laboratory shortly after each storm rainfall for soluble and total P and K analysis. Soil loss was estimated after drying at 105 °C. Soluble P and K contents were determined after filtration on a cellulose membrane with < 0.45 μm pore-diameter. In the filtrate, P concentration was determined in a UV–Vis spectrophotometer by Murphy and Riley (1962) method and soluble K in a flame emission spectrophotometer. Total P and K were determined after acid digestion (H2SO4 + H2O2) of 20 mL of water + sediment sample in the presence of saturated MgCl2 (Brookes and Powlson, 1981), then, using the amount of soil loss, the concentration of P and K in mg kg−1 were calculated.
tillage system, the minimum cultivation system with moldboard plow (MTo) decreased the percentage of soil cover by black oat residues (Fig. 3) and, thus, increased water loss in four of the eight monitored rainfall-events (September 22, October 13 and 17, and December 07, Fig. 4), and soil loss for five rainfall-events (September 22, 23 and 24, October 17, and November 05, Fig. 5). A large variability in runoff water losses (Fig. 4b) and runoff coefficient (Fig. 4c) was observed in the monitored storm rainfall events, which can be partially attributed to the total volume of rainfall (Fig. 4a). The same was also observed for soil loss (Fig. 5b), soluble and total P (Fig. 6b, c) and K (Fig. 7b, c). In spite of the great temporal variability of the soil loss results (Fig. 5), the sum of the soil losses during the eight monitored storm rainfall (Fig. 8b) shows that there were three main groups: (i) with soil losses ranging between 15 and 16 Mg ha−1 for those treatments without winter cover crops (CT and MTf), (ii) with soil losses ranging between 1.7 and 5.4 Mg ha−1 in those treatments grown with black oats in winter and with ridge, and (iii) the NT treatment, with total soil loss of only 0.2 Mg ha−1. On the other hand, the sum of water runoff losses was only possible in NT treatment (Fig. 8a). Although these differences between treatments are very clear, it is important to note that the monitoring covers a relatively short period (1 season) based on natural rainfall, which generated few events. Moreover, the spatial scale (1.2 m2) where losses were measured is a source of uncertainty. Ridge height and slope, slope of cultivation line and stone cover, among others, can also affect the results. Soluble P content in the runoff water was influenced by the tillage/ management systems in only two events (17th October 2004 and 5th November 2004 – Fig. 6b). The largest and smallest losses occurred, respectively, in the soil under no-tillage system with (NTrc and NTr) and without ridge (NT) construction (Fig. 6b). On the other hand, soluble K concentration in the runoff water was higher in NTr in two rainfall events compared to the other treatments (22th September and
2.5. Statistical analysis Data of plant dry-mass, degree of soil cover, soil and water losses, and losses of soluble and total P and K were submitted to analysis of variance at 5% probability of error and, subsequently, mean were compared using the Least Square Difference (LSD; α = 0.05). 3. Results Winter cover crop (black oats) prior to tobacco transplanting provided two to three times more dry-matter than soil under winter fallow. The amount of tobacco stems dry-matter left prior to the installation of the experiment was small (< 1.6 Mg ha−1), allowing for soil exposure to erosion processes (Table 4). Soil cover provided by tobacco plants was limited to < 25% of the soil surface, not differing between tillage/ management systems. Soil tillage for ridge construction in winterfallow soil (CT and MTf) exposed more than 60% of the soil surface, even 40 days after the transplanting of the seedlings. Compared to no-
Table 4 Dry mass of the cover plants and tobacco stems in different soil tillage/management systems. Tillage/management system
Winter soil cover
Winter plants (23th August 2004)
Tobacco stems (18th January 2005)
Mg ha−1 Conventional tillage (CT) Minimum tillage after fallow (MTf) Minimum tillage after oat (MTo) No-tillage with ridge (NTr) No-tillage with consolidated ridge (NTrc) No-tillage without ridge (NT)
Spontaneous Spontaneous Black oats Black oats Black oats Black oats
2.18c 2.23c 5.32ab 5.47ab 6.60a 4.90b
Means followed by the same letter do not differ (Least Square Difference, LSD; α = 0.05). 5
1.39abc 1.44abc 1.50ab 1.57a 1.31bc 1.25c
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Fig. 4. Rainfall (a), water losses (b) and runoff coefficient (c) in different rainfall events along the tobacco crop cycle, for soil under conventional tillage (CT), minimum tillage after fallow (MTf), minimum tillage after oat (MTo), no-tillage with ridge (NTr), no-tillage with consolidated ridge (NTrc), and no-tillage without ridge (NT). Means followed by the same letter do not differ (LSD, α = 0.05).
17th October 2004 – Fig. 7b). Total P (Fig. 6c) and K (Fig. 7c) concentration in the soil lost differed significantly among tillage/management systems in most rainfall events. There were higher concentrations of total P in sediments from the no-tillage system with ridge (NTrc and NTr). On the other hand, total P content in the soil lost from NT without ridge (NT) was the lowest in the four last rainfall events. By contrast, the highest total K concentration in sediments was observed in no-tilled treatments (NTcr, NTc, and NT), especially in the first three monitored rainfalls (Fig. 7c). By integrating the amount of soil lost transferred with the concentrations of P and K present in the sediment, the amount of these nutrients lost per unit area is obtained (Figs. 6d and 7d). As a consequence of the high soil losses due to soil tillage (CT) or winter fallow followed by ridging immediately before tobacco transplanting (MTf), the amount of P and K leaving the tobacco field-plots are much higher
compared to soil with proper winter cover combined with no-tillage system for tobacco cultivation (MTo, NTrc, NTr and NT). The sum of total P and K losses during the monitored storm rainfall events was 23 and 29 kg ha−1, respectively, in the treatments with winter fallow, ridge and grounding (CT and MTf – Fig. 8d). These losses were reduced about four times when growing black oats in the winter. But only NT without ridge was able to reduce 97 and 57 times the losses of P and K compared to CT. 4. Discussion 4.1. Crop treatment and soil cover The greatest losses of soil and water and the greatest values of runoff coefficient and soil loss occurred in conventional tillage and 6
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Fig. 5. Rainfall (a) and soil loss (b) in different rainfall events along the tobacco crop cycle, for soil under conventional tillage (CT), minimum tillage after fallow (MTf), minimum tillage after oat (MTo), no-tillage with ridge (NTr), no-tillage with consolidated ridge (NTrc), and no-tillage without ridge (NT). Means followed by the same letter do not differ (LSD, α = 0.05).
(Table 4). Throughout the crop cycle under no-tillage system, mulching loses its efficiency mainly because of the transit for crop treatments and leave harvest, while in the conventional plantation the increase of canopy cover by the tobacco plant is not sufficient to reduce soil and water losses (Antoneli and Thomaz, 2014). The no-tillage system alone clearly reduced erosion processes compared to conventional tillage. However, the reduction of soil losses can be potentiated when no-tillage is combined with the use of ridge from the previous year (NTrc) or without the use of ridges (NT). This ratifies that soil management aiming to reduce soil losses should use a combination of conservationist soil management practices, not just one practice, as also demonstrated by Merten et al. (2015). Tobacco-farming watersheds are hydrogeomorphologically impacted because of very-high transfer of soil (Merten and Minella, 2006), nutrients (Pellegrini et al., 2010) and agrochemical molecules to water bodies (Bortoluzzi et al., 2007; Sequinatto et al., 2013), including substances causing metabolic changes in fish (Becker et al., 2009). Furthermore, these farms are located in poor regions with food insecurity, intense deforestation, and high degree of pesticide-intoxicated people (Lecours et al., 2012).
minimum tillage with winter fallow because of intense soil tillage and low vegetation cover, with significant soil exposure to erosion processes. Lower soil and water losses and the lower runoff coefficient were due to the adoption of no-tillage system, regardless of the presence of ridge, natural soil consolidation and oats mulch. In the soil previously cultivated to black oats, minimum soil tillage for ridging show intermediate behavior between total soil inversion with intense tillage and no-tillage system. Tobacco plants produce a low amount of dry-matter since the crop has been genetically improved to combine leaves quantity and quality. In the case of Virginia-type tobacco, the leaves are harvested as they reach physiological maturity and, therefore, only the stems remain on the soil surface at the end of the crop-cycle. The amount of biomass remaining on the soil surface is extremely small and, even worse, stems provide negligible soil cover. Moreover, the amount of root biomass is also very small and is restricted to the ridge, distant 1.2 m from each other. The conventional tobacco production system, therefore, leaves the soil exposed to raindrop impact and overland water flow during the period from the first tillage until the ridging operation, along with a long period until the crop leaves contribute to soil cover. Later, when leave-harvesting begins, soil cover again decreases until exposing 100% of the soil surface. Cover crops during the winter period, such as black oats, on soils with very high nutrient contents will produce, as in the present experiment, a significant amount of biomass. In addition to protecting the soil during the period prior to tobacco transplantation, if no-tillage system or early ridge construction (MT) is adopted, soil cover during the growing stage of the commercial crop is guaranteed. In our study, the degree of soil cover was directly related to the dry-mass produced by the cultivated or spontaneous winter plants and in greater intensity with soil tillage. High soil exposure was mainly due to soil tillage after tobacco transplant, even though the amount of residue produced black oats in the winter was similar for the treatments MTo, NTrc, NTr and NT
4.2. Impact of soil management/tillage on water and soil losses Sediment yield in head-waters catchments under tobacco cultivation was 1.2 (Bonumá et al., 2014) to 3.0 (Antoneli and Thomaz, 2010) times greater in the crop harvesting phase (a 5-months period) compared to tobacco crop off-season, reflecting the intensive tillage and low surface cover of the soil. Under rainfall-simulation in a plot-scale, reduced runoff and total mass of suspended solids losses at the edge-offield were observed in strip- and no-till treatments compared to conventional-till in burley tobacco production system (Benham et al., 2007). The total soil loss on small runoff plots during the eight-storm rainfall monitored during tobacco crop cycle was 78 times greater in 7
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Fig. 6. Rainfall (a), soluble phosphorus losses (b), phosphorus concentration in the soil lost (c), and total phosphorus losses per area (d), for soil under conventional tillage (CT) management systems, minimum tillage after fallow (MTf), minimum tillage after oat (MTo), no-tillage with ridge (NTr), no-tillage with consolidated ridge (NTrc), and no-tillage without ridge (NT). Means followed by the same letter do not differ (LSD, α = 0.05).
CT and NT treatments in our study, there are differences of 1.6-fold, close to the 2-fold observed by Antoneli and Thomaz (2014). While no estimates are available in Brazil for soil losses from tobacco fields, in the USA these losses far exceed the state and national averages as well as soil loss tolerances (Wood and Worsham, 1986). The tolerance of 2.5 Mg ha−1 yr−1 is the lower limit presented by FAO (1967) for shallow soils, which more than 60% of this value was reach in only eight measured rainfall events during five months of monitoring of water, soil and nutrient losses during the tobacco cycle.
conventional-tilled (CT) tobacco than no-till (NT) tobacco, respectively the worst and the best management system for soil and water conservation. These losses are higher than those observed by Wood and Worsham (1986), namely 20 times greater on a sandy loam Aquic Hapludult with 1.3% slope, and lower that those observed by the authors of 90 times greater on a loamy sand Aquic Paleudults with 3.1% slope when comparing these two systems. Losses observed in our study are higher than the ~6-fold observed by Antoneli and Thomaz (2014) in shallow soil using animal traction. When comparing water losses in 8
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Fig. 7. Rainfall (a), soluble potassium losses (b), potassium concentration in the soil lost (c), and total potassium losses per area (d), for soil under conventional tillage (CT) management systems, minimum tillage after fallow (MTf), minimum tillage after oat (MTo), no-tillage with ridge (NTr), no-tillage with consolidated ridge (NTrc), and no-tillage without ridge (NT). Means followed by the same letter do not differ (LSD, α = 0.05).
were the responsible for high soil loss on 13 and 17 October 2004, where the runoff coefficient may explain the higher soil losses even with less total precipitation. On the other hand, the soil losses monitored during the rainfall-events on 03 and 05 November 2004 were very similar as a result of rainfall volume and runoff coefficient.
Soil losses varied with rainfall amount (e.g. rainfall-events monitored on September 21, 22 and 23, 2004), but mainly due to increase in soil antecedent moisture, with rise in the runoff coefficient. Even with less rain, there was an increase in soil losses during the rainfall-events occurred on 22 and 23 September 2004. Rainfall intensity and amount 9
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Fig. 8. Total losses of water (a), soil (b), soluble P and K (c) and total P and K (d) during the monitored rainfall-events events for soil under conventional tillage (CT) management systems, minimum tillage after fallow (MTf), minimum tillage after oat (MTo), no-tillage with ridge (NTr), no-tillage with consolidated ridge (NTrc), and no-tillage without ridge (NT). Means followed by the same letter do not differ (LSD, α = 0.05).
4.3. Impact of soil management/tillage on P and K losses
Initial or antecedent soil moisture is the dominant factor for infiltration and runoff, while rainfall intensity is the dominant factor influencing splash erosion and sediment outflow (Darvishan et al., 2015), and is responsible for most of the runoff in wet soil conditions (MolinaSanchis et al., 2016). As soil erosion processes are also dependent on runoff regardless of land use, Wei et al. (2007) observed that soil loss was more closely correlated to runoff than to rainfall. The largest amounts of runoff and soil loss were recorded in the soil water surplus phase, and the runoff coefficient was exponentially correlated to the inverse of antecedent soil water potential in the rainy season (Wei et al., 2007). In a parallel study, Reichert et al. (2019) observed tillage and ridging for tobacco cropping in the shallow soil reduced the effect of some soil physical stressors to tobacco growth and development. Furthermore, soil management systems with winter cover crop, ridging and reduced soil tillage increased flue-cured tobacco yield, cropped on shallow soils on steeplands. Increased biomass (roots and stalks) production is essential for soil quality and for water infiltration increase and runoff reduction. Finally, although not measured in our study, it is important to recognized the occurrence of tillage erosion on the studied site. The particular implement characteristics cause high spatial variability in soil redistribution patterns (De Alba et al., 2006), but generally soil loss occurs on convex areas and deposition takes place on concave areas. Loss of soil mass generates soil profile truncation on convexities and in upper areas of the cultivated hillslopes; while in concavities and lower areas of the field the opposite effect occurs, burying the original soil profile (De Alba et al., 2004). Rates of tillage soil translocation are proportional to slope gradient, while net rates of soil loss or gain are related to morphology and slope curvature (Lindstrom et al., 1992; Govers et al., 1994).
Ridging before transplanting or ridge maintenance for more than one cropping season, a premise of the no-tillage system, may induce greater losses of soluble nutrients, because of the difficulty of ‘injecting’ fertilizers into soil ridge. In contrast, losses of soluble K and P were low when fertilizers were added into the ridge in tilled soil in the CT, MTf and MTo treatments. Thus, the combination of no-tillage management, fertilizer application on the ridge, and the occurrence of rainfall soon after transplanting resulted in large bioavailable-nutrients transfer to aquatic bodies. The levels of soluble elements in the runoff water can be tens and even hundreds of times greater than those observed in waters draining non-anthropogenic areas (Pellegrini et al., 2010; Kaiser et al., 2015). In our study, soluble K contents reached 5 mg L−1 in soil with partial or total inversion during tillage (CT, MTf and MTo) and fertilization on the ridge, compared to values lower than 2.0 mg L−1 in the drainage network of our studied watershed during the period from January to August 2002 observed by Gonçalves et al. (2005). The quantities and forms of P and K transferred vary between rainfall events, because of variations in intensity and duration, time interval between rains, degree of soil cover (Sharpley et al., 1992), degree of saturation of soil colloids by the chemical element and fertilizer dose and time of application. Losses per unit area of P and K bound to sediments were dependent on the amount of soil lost. This is due to the high cation exchange capacity of the studied soil (Table 1), which contributes to the retention of K, and the high adsorption capacity of P due to the presence of Fe oxides in the clay fraction. When this soil reaches the water bodies, the amounts of P and K desorbed from the sediments to the water column may be much larger than the amount of elements desorbed in the soil from where it is originated as shown by Bortoluzzi et al. (2013). Water contamination by phosphates in watershed is facilitated by erosion processes and traditional tobacco cropping system due to high sediment concentration and low organic 10
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carbon (Pellegrini et al., 2010). Sediment concentration and quality are related to fertilization and selectivity of erosion, where the finest and richest soil fraction is selectively transported (Mendonça et al., 2015; Bertol et al., 2017). These losses were minimized with the increase of soil cover and decrease in tillage, because the magnitude of nutrient losses was associated with the amount of soil lost. As a consequence, the reduction in the productive capacity of the soil will occur in the medium and long term, requiring greater fertilizer applications to compensate the losses. It is important to note that the losses of P and K evaluated in the present study are only related to losses due to surface runoff. An important component is losses by leaching, especially in shallow soils with high bioavailable P and K content as in the present study (Table 1) that has not been evaluated and should be taken into account in future studies. In some cases, depending on the soil depth, the application of fertilizers directly into the ridges can even increase the potential for leaching losses and should be avoided.
systems in Southwest Virginia. Water Air Soil Poll 179, 159–166. https://doi.org/10. 1007/s11270-006-9221-z. Bertol, I., Luciano, R.V., Bertol, C., Bagio, B., 2017. Nutrient and organic carbon losses, enrichment rate, and cost of water erosion. Rev. Bras. Cienc. Solo 41, e0160150. https://doi.org/10.1590/18069657rbcs20160150. Bonumá, N.B., Rossi, C.G., Arnold, J.G., Reichert, J.M., Minella, J.P.G., Allen, P.M., Volk, M., 2014. Simulating landscape sediment transport capacity by using a modified SWAT model. J. Environ. Qual. 43, 55–66. https://doi.org/10.2134/jeq2012.0217. Bortoluzzi, E.C., Rheinheimer, D.S., Gonçalves, C.S., Pellegrini, J.B.R., Maroneze, A.M., Kurz, M.H.S., Bacar, N.M., Zanella, R., 2007. Investigation of the occurrence of pesticide residues in rural wells and surface water following application to tobacco. Quim Nova 30, 1872–1876. https://doi.org/10.1590/S0100-40422007000800014. Bortoluzzi, E.C., Rheinheimer, D.S., Santanna, M.A., Caner, L., 2013. Mineralogy and nutrient desorption of suspended sediments during a storm event. J Soil Sedim 13, 1093–1105. https://doi.org/10.1007/s11368-013-0692-4. Brookes, P.C., Powlson, D.C., 1981. Preventing phosphorus losses during perchloric acid digestion of sodium bicarbonate soil extracts. J. Sci. Food Agr. 32, 671–674. https:// doi.org/10.1002/jsfa.2740320707. Dalmolin, R.S.D., Pedron, F.A., Azevedo, A.C., Zago, A., 2003. Levantamento semidetalhado de solos da microbacia do arroio Lino – município de Agudo (RS). 2003 (84p). Darvishan, A.K., Banasik, K., Sadeghi, S.H., Gholami, L., Hejduk, L., 2015. Effects of rain intensity and initial soil moisture on hydrological responses in laboratory conditions. Int. Agrophys. 29, 165–173. https://doi.org/10.1515/intag-2015-0020. De Alba, S., Lindstrom, M., Schumacher, T.E., Malo, D.D., 2004. Soil landscape evolution due to soil redistribution by tillage: a new conceptual model of soil catena evolution in agricultural landscapes. Catena 58, 77–100. https://doi.org/10.1016/j.catena. 2003.12.004. De Alba, S., Borselli, L., Torri, D., Pellegrini, S., Bazzoffi, P., 2006. Assessment of tillage erosion by mouldboard plough in Tuscany (Italy). Soil Tillage Res. 85, 123–142. https://doi.org/10.1016/j.still.2004.12.002. FAO - Food and Agriculture Organization of the United Nations, 1967. La erosión del suelo por el agua: Algunas medidas para combatirla en las tierras de cultivo. Organización de las Naciones Unidas, Roma (207p). Fullen, M.A., 1985. Compaction, hydrological processes and soil erosion on loamy sands in east Shropshire, England. Soil Till. Res. 6, 17–29.. https://doi.org/10.1016/01671987(85)90003-0. Gonçalves, C.S., Rheinheimer, D.S., Pellegrini, J.B.R., Kist, S.L., 2005. Qualidade da água numa microbacia hidrográfica de cabeceira situada em região produtora de fumo. Rev. Bras. Eng. Agric. Ambient. 9, 391–399. https://doi.org/10.1590/S141543662005000300015. Govers, G., Vandaele, K., Desmet, P.J.J., Poesen, J., Bunte, K., 1994. The role of tillage in soil redistribution on hillslopes. Eur. J. Soil Sci. 45, 469–478. https://doi.org/10. 1111/j.1365-2389.1994.tb00532.x. IUSS Working Group WRB, 2014. World Reference Base for Soil Resources 2014. International Soil Classification System for Naming Soils and Creating Legends for Soil Maps. FAO, Rome, Italy, pp. 203. Kaiser, D.R., Reinert, D.J., Reichert, J.M., Streck, C.A., Pellegrini, A., 2010. Nitrate and ammonium in soil solution in tobacco management systems. Rev. Bras. Cienc. Solo 34, 379–388. https://doi.org/10.1590/S0100-06832010000200011. Kaiser, D.R., Sequinatto, L., Reinert, D.J., Reichert, J.M., Rheinheimer, D.S., Dalbianco, L., 2015. High nitrogen fertilization of tobacco crop in headwater watershed contaminates subsurface and well waters with nitrate. J. Chem. 1–11. https://doi.org/ 10.1155/2015/375092. Kerr, J.G., Burford, M.A., Olley, J.M., Bunn, S.E., Udy, J., 2011. Examining the link between terrestrial and aquatic phosphorus speciation in a subtropical catchment: the role of selective erosion and transport of fine sediments during storm events. Water Res.Water Res 45, 3331–3340. https://doi.org/10.1016/j.watres.2011.03.048. Lecours, N., Almeida, G.E.G., Abdallah, J.M., Novotny, T.E., 2012. Environmental health impacts of tobacco farming: a review of the literature. Tob. Control.Tob. Control 21, 191–196. https://doi.org/10.1136/tobaccocontrol-2011-050318. Maluf, J.R.T., 2000. Nova classificação climática do Estado do Rio Grande do Sul. Rev. Bras. Agrometeorol. 8, 141–150. Mendonça, P.G., Silva Júnior, J.F., Oliveira, I.R., Teixeira, D.B., Moitinho, M.R., Martins Filho, M.V., Marques Júnior, J., Pereira, G.T., 2015. Spatial uncertainty of nutrient loss by erosion in sugarcane harvesting scenarios. Rev. Bras. Cienc. Solo 39, 1181–1189. https://doi.org/10.1590/01000683rbcs20140432. Merten, G.H., Minella, J.P.G., 2006. Impact on sediment yield caused by intensification of tobacco production in a catchment in southern Brazil. Cienc. Rural 36, 669–672. https://doi.org/10.1590/S0103-84782006000200050. Merten, G.H., Araújo, A.G., Biscaia, R.C.M., Barbosa, G.M.C., Conte, O., 2015. No-till surface runoff and soil losses in southern Brazil. Soil. Till. Res. 152, 85–93. https:// doi.org/10.1016/j.still.2015.03.014. Minella, J.P.G., Merten, G.H., Reichert, J.M., Santos, D.R., 2007. Identificação e implicações para a conservação do solo das fontes de sedimentos em bacias hidrográficas. Rev. Bras. Cienc. Solo 31, 1637–1646. https://doi.org/10.1590/ S0100-06832007000600039. Minella, J.P.G., Merten, G.H., Walling, D.E., Reichert, J.M., 2009. Changing sediment yield as an indicator of improved soil management practices in southern Brazil. Catena 79, 228–236. https://doi.org/10.1016/j.catena.2009.02.020. Molina-Sanchis, I., Lázaro, R., Arnau-Rosalén, E., Calvo-Cases, A., 2016. Rainfall timing and runoff: the influence of the criterion for rain event separation. J. Hydrol. Hydromech. 64 (63), 226–236. https://doi.org/10.1515/johh-2016-0024. Murphy, J., Riley, J.P., 1962. A modified single solution method for the determination of phosphate in natural waters. Anal. Chim. Acta 27, 31–36. https://doi.org/10.1016/ S0003-2670(00)88444-5.
5. Conclusion The widespread use of intense soil tillage and the ridging before tobacco transplanting and for grounding of growing plants favor soil degradation and the increase in soil, water and nutrient losses, which are aggravated by winter fallow. Soil exposure coincides with the rainy season, with higher rainfall volume on high-moisture soil. Conservation tillage/management systems for tobacco cultivation, including the use of winter cover crops such as black oats and minimal soil mobilization for ridge construction and maintenance, are alternatives indicated for tobacco farmers once it resulted in drastic reduction in losses of soil, water, phosphorus and potassium (especially adsorbed to the sediments). However, the addition of fertilizers inside the ridge is mandatory; otherwise it will strongly increase the transfer of bioavailable phosphorus and potassium to surface-water bodies, increasing the potential for eutrophication promoted by phosphorus input, and unnecessarily increasing the costs of production with the replacement of fertilizers. Acknowledgments We thank to CNPq (Brazilian National Council for Scientific and Technological Development) for fellowship for the first and last authors, CAPES (Coordination for the Improvement of Higher Education Personnel) for graduate student scholarships, and FAPERGS (Rio Grande do Sul State Research Foundation) and CNPq for research grant and undergraduate scholarships. References AFUBRA. 2016. Associação dos Fumicultores do Brasil. Fumicultura, 2016. Acesso em: 13/04/2017. Disponível em: < http://www.afubra.com.br > . Alameda, D., Anten, N.P.R., Villar, R., 2012. Soil compaction effects on growth and root traits of tobacco depend on light, water regime and mechanical stress. Soil Tillage Res. 120, 121–129. https://doi.org/10.1016/j.still.2011.11.013. Álvares, C.A., Stape, J.L., Sentelhas, P.C., Goncalves, J.L.M., Sparovek, G., 2013. Koppen’s climate classification map for Brazil. Meteorologische Zeitschrif 22, 711–728. https://doi.org/10.1127/0941-2948/2013/0507. Antoneli, V., Thomaz, E.L., 2010. Relação entre o cultivo de fumo (Nicotiana tabacum) e a produção de sedimentos na Bacia do Arroio Boa Vista, Guamiranga - PR. Geografia 35, 383–398. Antoneli, V., Thomaz, E.L., 2014. Perda de solo em cultivo de tabaco sob diferentes formas de cultivo na região Sudeste do Paraná. Rev. Bras. Geomorfol. 15, 455–469. https://doi.org/10.20502/rbg.v15i3.534. Bagio, B., Bertol, I., Wolschick, N.H., Schneiders, D., Santos, M.A.N., 2017. Water erosion in different slope lengths on bare soil. Rev. Bras. Cienc. Solo 41, e0160132. https:// doi.org/10.1590/18069657rbcs20160132. Becker, A.G., Moraes, B.S., Menezes, C.C., Loro, V.L., Rheinheimer, D.S., Reichert, J.M., Balsisserotto, B., 2009. Pesticide contamination of water alters the metabolism of juvenile silver catfish, Rhamdia quelen. Ecotoxicol. Environ. Saf. 72, 1734–1739. https://doi.org/10.1016/j.ecoenv.2009.01.006. Benham, B.L., Vaughan, D.H., Laird, M.K., Ross, B.B., Peek, D.R., 2007. Surface water quality impacts of conservation tillage practices on burley tobacco production
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Catena 183 (2019) 104215
J.M. Reichert, et al.
Sequinatto, L., Reichert, J.M., Rheinheimer, D.S., Reinert, D.J., Copetti, A.C.C., 2013. Occurrence of agrochemicals in surface waters of shallow soils and steep slopes cropped to tobacco. Quim NovaQuim. Nova 36, 768–772. 2013. https://doi.org/10. 1590/S0100-40422013000600004. Sharpley, A.N., Smith, S.J., Jones, O.R., 1992. The transport of bioavailable phosphorus in agricultural runoff. J. Environ. Qual. 21, 30–35. https://doi.org/10.2134/jeq1992. 00472425002100010003x. Sloneker, L.L., Moldenhauer, W.C., 1997. Measuring the amounts of crop residue remaining after tillage. J. Soil Water Conserv. 32, 231–236. Tiecher, T., Caner, L., Minella, J.P.G., Evrard, O., Mondamert, L., Labanowski, J., Rheinheimer, D.S., 2017a. Tracing sediment sources using mid-infrared spectroscopy in Arvorezinha catchment, southern Brazil. Land Deg. Dev. 28, 1603–1614. https:// doi.org/10.1002/ldr.2690. Tiecher, T., Schenato, R.B., Santanna, M.A., Caner, L., Rheinheimer, D.S., 2017b. Phosphorus forms in sediments as indicators of anthropic pressures in an agricultural catchment in southern Brazil. Rev. Bras. Cienc. Solo 41, e0160569. https://doi.org/ 10.1590/18069657rbcs20160569. Tiecher, T., Ramon, R., Laceby, J.P., Evrard, O., Minella, J.P.G., 2019. Potential of phosphorus fractions to trace sediment sources in a rural catchment of southern Brazil: comparison with the conventional approach based on elemental geochemistry. Geoderma 337, 1067–1076. https://doi.org/10.1016/j.geoderma.2018.11.011. Turšić, I., Mesić, M., Kisić, I., Racz, A., 2016. Influence of bulk density on soil resistance and yield of tobacco. Int. J. Plant Res. 6, 21–24. https://doi.org/10.5923/j.plant. 20160602.01. Wei, L., Zhang, B., Wang, M., 2007. Effects of antecedent soil moisture on runoff and soil erosion in alley cropping systems. Agr. Water Manage. 94, 54–62. https://doi.org/10. 1016/j.agwat.2007.08.007. Wood, S.D., Worsham, A.D., 1986. Reducing soil erosion in tobacco fields with no-tillage transplanting. J. Soil Water Conserv. 41, 193–196.
Oliveira, F.P., Buarque, D.C., Vieiro, A.C., Merten, G.H., Cassol, E.A., Minella, J.P.G., 2012. Fatores relacionados à suscetibilidade da erosão em entressulcos sob condições de uso e manejo do solo. Rev. Bras. Eng. Agric. Ambient. 16, 337–346. https://doi. org/10.1590/S1415-43662012000400002. Pellegrini, J.B.R., Rheinheimer, D.S., Gonçalves, C.S., Copetti, A.C.C., Bortoluzzi, E.C., Tessier, D., 2010. Impacts of anthropic pressures on soil phosphorus availability, concentration, and phosphorus forms in sediments in a southern Brazilian watershed. J. Soils SedimentsJ. Soil. Sediment. 10, 451–460. https://doi.org/10.1007/s11368009-0125-6. Petry, C., Rheinheimer, D.S., Kaminski, J., Pessoa, A.C.S., Cassol, L.C., 1994. Influência do estresse de alumínio em plantas de fumo: II. Efeito nos parâmetros cinéticos de absorção de fósforo. Rev. Bras. Cienc. Solo 18, 69–72. https://doi.org/10.1590/ S0100-06832000000300007. Ramon, R., Minella, J.P.G., Merten, G.H., Barros, C.A.P., Canale, T., 2016. Kinetic energy estimation by rainfall intensity and its usefulness in predicting hydrosedimentological variables in a small rural catchment in southern Brazil. Catena 148, 176–184. https://doi.org/10.1016/j.catena.2016.07.015. Reichert, J.M., Norton, L.D., Favaretto, N., Huang, C., Blume, E., 2009. Settling velocity, aggregate stability, and interrill erodibility of soils varying in clay mineralogy. Soil Sci. Soc. Am. J. 73, 1369–1377. https://doi.org/10.2136/sssaj2007.0067. Reichert, J.M., Pellegrini, A., Rodrigues, M.F., 2019. Tobacco growth, yield and quality affected by soil constraints on steeplands. Ind. Crop. Prod.Ind. Crops Prod. 128, 512–526. https://doi.org/10.1016/j.indcrop.2018.11.037. Reichert, J.M., Amado, T.J.C., Reinert, D.J., Rodrigues, M.F., Suzuki, L.E.A.S., 2016. Land use effects on subtropical, sandy soil under sandyzation/desertification processes. Agric. Ecosyst. Environ 233, 370–380. https://doi.org/10.1016/j.agee.2016.09.039. Rheinheimer, D.S., Petry, C., Kaminski, J., Bartz, H.R., 1994. Influência do estresse de alumínio em plantas de fumo: I. Efeitos no sistema radicular, na absorção de fósforo e cálcio e no acúmulo de massa seca. Rev. Bras. Cienc. Solo 18, 63–68.
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