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Phosphorus and potassium budget in the soil–plant system in crop rotations under no-till
Soil & Tillage Research 126 (2013) 127–133
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Phosphorus and potassium budget in the soil–plant system in crop rotations under no-till C.A. Rosolem *, J.C. Calonego Department of Crop Science, College of Agricultural Sciences, Sa˜o Paulo State University, Botucatu, SP, Brazil
A R T I C L E I N F O
A B S T R A C T
Article history: Received 12 March 2012 Received in revised form 2 August 2012 Accepted 4 August 2012
Soil management and crop rotations can affect P and K budget in soil, decreasing losses, and increasing fertilizer use efficiency. The P and K budget in the soil–plant system at depths up to 60 cm was studied for different soil managements and crop rotations under no-till for three years in Botucatu, Sa˜o Paulo, Brazil. The investigated crop rotations were: triticale (X Triticosecale) and sunflower (Helianthus annuus) cropped in autumn–winter; pearl millet (Pennisetum glaucum), forage sorghum (Sorghum bicolor), and Sunn hemp (Crotalaria juncea) were grown in the spring, as well as an additional treatment with chiseling followed by a fallow period; and soybean (Glycini max, L., Merril) was cropped in the summer. Each year triticale and sunflower were grown in plots and pearl millet, forage sorghum, Sunn hemp and of chisel/ fallow in sub-plots. The triticale/millet rotation led to the largest decrease in available P within the 0– 0.60 m layer of the soil profile and the largest K increase within the 0–0.05 m layer. Potassium mobility in the soil profile and the increases in the available K content in the 0.40–0.60 m layer were independent of the management system. Crop rotations with or without chiseling are not effective in preventing soil P losses. There is considerable K leaching below 0.60 m, but chiseling and the use of high K accumulating plants as triticale results in lower K losses. ß 2012 Elsevier B.V. All rights reserved.
Keywords: Cover crops Management soil Nutrient cycling
1. Introduction Nutrients in soil solution can be taken up by plants, leached, lost to the atmosphere, or transformed into non-labile forms. The fate of nutrients available in the soil depends on root access, plant demand, exports via harvesting, and soil physical, chemical and mineralogical conditions. In highly weathered tropical soils, with predominance of 1:1 clay minerals and sesquioxides, phosphorus (P) availability is low because most of it is in non-labile forms, while potassium (K) availability may be decreased via leaching (Novais et al., 2007). An adequate soil management and crop rotations can reduce these losses and increase fertilizer use efficiency by increasing nutrient storage in the soil–plant system (Sousa and Lobato, 2004), and promoting nutrient recycling (Foloni and Rosolem, 2008; Foloni et al., 2008; Garcia et al., 2008). Crop residues deposited on the soil surface in areas under no-till (NT) provide considerable nutrient reserves (Carpim et al., 2008). Thus, crop residues that remain on the soil surface, in addition to protecting against climatic effects and erosion, are mineralized, releasing nutrients that can be used by future crops (Borkert et al., 2003). Some nutrients, such as K, can be washed directly to the soil
Abbreviations: NT, no-till; AO, organic acid. * Corresponding author. Tel.: +55 18 3880 7161; fax: +55 14 3880 7000. E-mail address: [email protected] (C.A. Rosolem). 0167-1987/$ – see front matter ß 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.still.2012.08.003
via rainfall, independent of the degree of organic matter mineralization (Rosolem et al., 2003, 2007; Calonego et al., 2005). According to a review by Pavinato and Rosolem (2008), adding plant material to soil also causes rapid increases in organic acid (OA) concentrations, which occur through organic matter decomposition, direct leaf run-off, and root and microbial exudates production. Due to their anionic character, these OAs interact with the soil solid phase and occupy P adsorption sites. In addition, they can form stable complexes with aluminum (Al) and iron (Fe) that prevent these metals from reacting with P (Sposito, 1989). Thus, under NT, the straw left on the soil surface may play an important role in reducing P fixation in the soil, increasing phosphate fertilization efficiency and affecting P balance in the system. According to Franchini et al. (1999), these organic compounds also increase the percentages of calcium (Ca), magnesium (Mg), and K in the soil cation exchange capacity (CEC) due to the complexation of Al ions, which can reduce nutrient losses due to leaching, especially K. However, according to Pavinato and Rosolem (2008), the efficiency of OAs in increasing soil nutrient availability depends on factors such as the type and persistence of these compounds, which are controlled by the management system and cultivated species. Hence the crop rotation my also affect the nutrient balance in the system. In NT systems, cover crop rotations (or green manure) are intended to not only protect the soil surface but also to improve its physical, chemical, and biological attributes, even at deeper
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depths, through the effect of roots. This improved soil profile may increase the efficiency of water and fertilizer use, and distinct crop rotations, by exploring different soil regions or layers, can contribute to avoid leaching, balance the soil nutrients, increase fertility, and improve mineral fertilizer use. Crop rotations play an important role in nutrient recycling because plant species vary in their abilities to produce biomass, absorb ions efficiently, and exploit nutrients at different soil depths (Mengel and Kirkby, 1987). Each of these characteristics should be considered in fertilizer management program. The objective of this study were to evaluate the P and K budget in the soil profile at depths down to 0.60 m as affected by soil management systems and crop rotations. 2. Materials and methods 2.1. Experimental site and treatments An experiment was conducted in Botucatu, Sa˜o Paulo, Brazil, 228490 S, 488250 W and 786 m altitude, for three years on a Typic Rhodudalf (Soil Survey Staff, 2006), clay, with depth greater than 2 m and with 60% to 79% of kaolinite and 13% to 20% of gibbsite. Before this experiment, the area had been under NT for 6 years, with a soybean/black oats/corn/triticale rotation. The climate, according to Ko¨ppen classification is CWa, that is, a subtropical humid climate with dry winter. The dry season is well-defined between May and September. The mean rainfall average is approximately 1400 mm, the highest monthly mean temperature is over 22 8C and the lowest is below 18 8C (Fig. 1). Before starting the experiment, the soil was sampled for chemical (Raij et al., 2001) and physical analyses (Smith and Mullins, 1991) down to 0.60 m (Table 1). Treatments consisted of cropping triticale (X Triticosecale Wittmack) and sunflower (Helianthus annuus) in the fall-winter (May to August in the three years), followed by pearl millet (Pennisetum glaucum L.), forage sorghum (Sorghum bicolor (L.) Moench) or Sunn hemp (Crotalaria juncea L.) cropped in the spring (October and November in the three years), plus an additional treatment that was chiseled (in September of the first year) and kept fallow during the springs. Soybean (Glycine max L.,Merril) was cropped in the summer (December through April in the three years) in all the plots. Details of the rotations are presented in Table 2. The experimental design was a split-plot in complete
randomized blocks, with four replications. Triticale and sunflower were grown in the plots in the fall/winter with pearl millet, sorghum, Sunn hemp, and chiseling/falow in sub-plots. Plots were 8.0 m 32.0 m, and sub-plots were 8.0 m 5.0 m, with 4.0 m between blocks, plots and sub-plots. Soybean and sunflower were planted in rows 0.45 m apart from each other. The other crops were planted at a spacing of 0.17 m between rows. The chisel plow had seven shanks mounted on two parallel bars on a square tool carrier. The shanks, inclined 258 forward, were set 0.60 m apart resulting in an effective between-shank spacing of 0.30 m, with a maximum operating depth of 0.30 m. A clodbreaking roller was attached to break the biggest clods, decrease surface roughness and avoid disking. The soil was chiseled only once, after the fall-winter crops in the first year, and the chiseled plots were left fallow between the winter and summer crops thereafter. In fallow plots the weeds were hoed as required. Each year soybean received no N, 26.5 kg ha1 of P and 50 kg ha1 of K as triple superphosphate and potassium chloride, and pearl millet and sorghum received 40 kg ha1 of N as urea at planting. Sunflower and triticale received no fertilizers. Triticale and sunflower grains were not harvested because the yields were very low; hence, the plants were left to naturally lodge. Pearl millet, sorghum and Sunn hemp were desiccated with ghyphosate at 57, 50 and 62 days after plant emergence, respectively in the first, second and third years. 2.2. Sample collection and analysis In December of the last year of the experiment, immediately before soybean planting, pearl millet, forage sorghum and Sunn hemp were sampled, using 0.25 m 0.25 m wooden frames. Five sub-samples were randomly taken from each subplot and combined in one. This material was oven dried at 65 8C for three days to determine dry matter yield. A subsample was ground for P and K analysis (Malavolta et al., 1997) and the rest of the material was returned to the respective plots. Using the dry matter and nutrient concentrations, the amount of P and K in the remains of plant residues on soil surface at soybean planting was calculated. At the same time, soil was sampled at depths from 0 to 0.05, 0.05 to 0.10, 0.10 to 0.20, 0.20 to 0.40 and 0.40 to 0.60 m. Three subsamples were taken per subplot and combined in one, air dried, passed through a 2 mm sieve and analyzed for available P (resin) and exchangeable K according to Raij et al. (2001). The mass
Fig. 1. Rainfall and temperature (monthly average) during April 2003 and December 2005. Vertical arrows show when operations were realized.
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Table 1 Selected chemical and physical properties of the soil at the beginning of the experiment. Chemical properties Depth (m)
pHCaCl2
OM (g dm3)
Presin (mg dm3)
H + Al (mmolc dm3)
K (mmolc dm3)
Ca (mmolc dm3)
Mg (mmolc dm3)
CEC (mmolc dm3)
0–0.05 0.05–0.10 0.10–0.20 0.20–0.40 0.40–0.60
5.4 4.6 4.6 4.8 5.1
32 27 26 22 22
37 26 15 3 2
56 91 97 69 63
4.7 3.0 2.5 1.1 0.2
37 28 35 46 57
16 11 16 15 11
114 134 150 131 132
Physical properties Depth (m)
0–0.05 0.05–0.10 0.10–0.20 0.20–0.40 0.40–0.60
SPRa (MPa)
1.4 2.8 2.3 2.3 1.8
Soil moistureb (g g1)
0.29 0.29 0.34 0.38 0.42
Bulk density (g cm3)
1.22 1.39 1.38 1.29 1.31
Porosity Total (m3 m3)
Macro (m3 m3)
Micro (m3 m3)
0.57 0.53 0.52 0.50 0.58
0.11 0.08 0.07 0.05 0.05
0.42 0.42 0.45 0.45 0.48
Textural properties Depth (m)
Sand (g kg1)
Clay (g kg1)
Silt (g kg1)
0–0.05 0.05–0.10 0.10–0.20 0.20–0.40 0.40–0.60
137 131 128 110 88
571 598 599 645 715
292 272 273 245 197
a b
SPR, soil penetration resistance. Soil water content at the time penetration resistance was measured (April 2003).
of available P and K were calculated considering their concentrations, soil bulk density and soil volume. Considering soil P and K available in April of the first year and after three years, equation 1 was used to estimate the variation in soil P and K mass in each soil layer (down to 0.60 m):
difference between total inputs and utilization. Results greater and smaller than zero were considered as ‘‘gains’’ or ‘‘losses’’ in the soil–plant system, respectively, down to 0.60 m in the soil profile, which were estimated using Eq. (2): Budget ¼ ððNfert þ Nsi Þ ðNexp þ Ncc ÞÞ Nsf
Dsoil ¼ N soil initial Nsoil final
where Dsoil is the variation in available P and K in the soil profile down to 0.60 m, between April of the first year and December of the last year of the experiment; Nsoil initial is the P and K available in the soil profile in April of the first year; Nsoil final is the P and K available in the soil profile in December of the last year. In the P and K budget in the soil–plant system were considered the exports by soybean grown in the first and second year of the experiment. Nutrient exports were estimated using the grain yields and P and K concentrations in the grain, determined as in Malavolta et al. (1997). To calculate P and K budget in the soil–plant system, initial available P and K in the soil down to 0.60 m were added to the fertilizer applied (53 and 100 kg ha1, respectively), and this was taken as inputs. The quantities exported with the soybean grains (two harvests) plus the amount present in the above ground material in December of the last year of the experiment were considered as ‘‘utilized’’ by plants. The P and K residual (final) amount in the soil down to 0.60 m was subtracted from the Table 2 Crop rotations and treatments. Summer
Fall/winter (plots)
Spring (sub-plots)
Soybean
Triticale
Pearl millet Forage sorghum Sun hemp Chiseling/fallow Pearl millet Forage sorghum Sun hemp Chisel/fallow
Sunflower
(2)
(1) where Budget is the diference in P and K amount in the system between April of the first and December of the last year; Nfert is P or K in the fertilizer applied; Ncc is P or K accumulated in the cover crops; Nexp is P and K exported by soybean; Nsi is the initial; and Nsf is the final available P and K in the soil profile down to 0.60 m. 2.3. Statistical analysis In spite of the original split-plot design, all data were collected randomly, and descriptive statistics was applied, and the mean standard errors were calculated and used to compare the results. 3. Results and discussion The available P content in the topsoil increased after 3 years, with the exception of the triticale/millet and triticale/Sunn hemp rotations, in which P decreased within the 0–0.05 m and 0.05– 0.10 m layers, respectively. There were no variations in P content in the 0.05–0.10 m layers of the triticale/millet and triticale/ chisel + fallow rotations (Table 3). These results cannot be explained by P accumulation in the cover crops at the time of soil sampling because systems involving chiseling + fallow also resulted in increased P at the soil surface. Considering that the same amount of fertilizer was added to all rotations, and the amount of P exported by soybeans did not vary much (Table 4), the higher available P content in the surface soil layers indicates that system losses were reduced. In this case, the increase may be due to decreased P fixation or solubilization of less labile P forms in the soil (Andrade et al., 2003; Sposito, 1989). Growing Sunn hemp, generally a species with small root system (Calonego and Rosolem, 2010), resulted in the largest increase in the available P content in
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Table 3 Difference (Dsoil) between the initial (April 2003) and final (December 2005) amounts of P, in kg ha1, in the soil profile,a as affected by crop rotations and soil management (fall-winter/spring). Depth (m)
Treatments Sun flower
Triticale
Millet (kg ha1) 0–0.05 0.05–0.10 0.10–0.20 0.20–0.40 0.40–0.60 S(0–60)
6 2 5 3 0 0
Sorghum (kg ha1)
(3)b (5) (6) (1) (1) (7)
2 5 8 3 0 4
Sunn hemp (kg ha1)
(4) (4) (3) (1) (1) (8)
11 5 7 3 1 5
a
Dsoil = Psoil initial Psoil final, where Psoil initial = 58 kg ha1.
b
Values in parenthesis show the mean standard error.
Chiseling (kg ha1)
(4) (3) (3) (1) (2) (6)
2 5 7 2 1 3
the surface layer. Furthermore, decreased P content was observed in the 0–0.05 m layer in the triticale/millet system, coinciding with increased root production (Calonego and Rosolem, 2010). Therefore, differences in P accumulation in the roots at the time of soil sampling may have affected the resulting soil P contents. More Psolubilizing bacteria are present in legumes than in grasses (Sylvester-Bradley et al., 1982), and as the P content in plant tissues depends on mineralization for the nutrient to become available (Teixeira et al., 2009), Sunn hemp, a legume presenting a low C/N ratio, may have released more P back into the soil compared with the grasses. In addition, N fixing legumes take up more cationic than anionic nutrients, resulting in rizosphere acidification and increased P availability (Aguilar and Van Diest, 1981). However, De-Maria and Castro (1993) observed a higher P content in soil cropped to black oat compared with Sunn hemp after seven years of an annual crop rotation, which would have allowed time for root mineralization and thus increased the P content in the soil. Therefore, differences in P behavior in the soil profile under different crop rotation management systems can be attributed to the effects on P fixation, solubilization of less labile forms, and P accumulation by undecomposed roots. In the 0.10–0.20 m soil layer, the amount of available P decreased, probably because root activity is high at this depth. Studies to determine the presence of active roots throughout the soil profile by indirect methods (Bo¨hm, 1979; Encide-Olibone et al., 2008) show that root activity of grasses, forest species, and soybeans can reach 30% at a depth of 0.20 m (Kulmatiski et al., 2010; Pivetta et al., 2011) and 90% at a depth of 0.10 m (Pivetta et al., 2011). Thus, as P additions occur in the topsoil and the nutrient mobility low, the result is a P depletion in the 0.10–0.20 m
(2) (4) (3) (1) (1) (4.8)
Millet (kg ha1)
Sorghum (kg ha1)
2 0 8 1 0 11
10 8 7 3 0 8
(3) (4) (3) (2) (2) (5)
(3) (5) (4) (1) (1) (6)
Sunn hemp (kg ha1) 8 3 6 0 1 0
(5) (3) (3) (1) (1) (5)
Chiseling (kg ha1) 7 0 8 2 1 4
(4) (4) (2) (2) (1) (5)
soil layer and an accumulation in the 0–0.10 m layer under some crop rotations. The available P content in the soil profile decreased under sunflower/sorghum, sunflower/chisel + fallow, triticale/millet, and triticale/chisel + fallow rotations and increased under the sunflower/Sunn hemp and triticale/sorghum. The 3-year consecutive succession of triticale/millet promoted the greatest P deficit in the soil profile, decreasing the available P by 11 kg ha1, whereas growing triticale/sorghum resulted in the greatest P increase in the profile, increasing its availability by 8 kg ha1 (Table 3). The greatest P decrease in the 0–0.60 m layer, in the triticale/millet treatment, was more affected by the decrease in available P than by the increased exportation or immobilization by the cover crops (Table 4). However, in a study by Foloni et al. (2008), millet exhibited the highest P accumulation in plant tissues, which led to a greater decrease in the soil available P and so to a less prone P fixation. The increased P availability in the soil profiles under triticale/sorghum and sunflower/Sunn hemp (Table 3) is related to the greater available P content observed in the final evaluation, given that the cover crops did not accumulate considerable amounts of P and that P export by soybeans was similar between treatments (Table 4). Overall, after 3 years of crop rotations, the P content decreased in the system by amounts ranging from 17 to 37 kg ha1 (Table 4). Part of this decrease can probably be attributed to the P fixation process, which makes P unavailable to plants. The differences in the amounts of P lost from the soil–plant system across treatments are related to differences between the plants, such as their ability to solubilize P (transforming it into an organic form), the intensity of soil tillage, the occurrence of microbial activity able to solubilize
Table 4 Budget of P (kg ha1) in the soil plant system as affected by P inputs and outputs from the soil–plant system in each crop rotations and soil management. P in the soil–plant system
Treataments Sun flower
Triticale 1
Millet (kg ha Pfert a Pcc b Pexp c Psi d Psf e Budgetg a b c d e f g
53 17 18 58 58 17
)
(3)f (2) (7) (9)
P added as fertilizer (accumulated over two years). P accumulated in cover crop shoots. P exported by grains (accumulated over two years). Initial available P in the soil profile (0–60 cm). Final available P in the soil profile (0–60 cm). Values in parenthesis show the mean standard error. Budget = ((Pfert + Psi) (Pexp + Pcc) Psf)
Sorghum (kg ha1)
Sunn hemp (kg ha1)
Chiseling (kg ha1)
Millet (kg ha1)
Sorghum (kg ha1)
Sunn hemp (kg ha1)
Chiseling (kg ha1)
53 11 16 58 54 30
53 8 17 58 63 22
53 19 (2) 58 55 (5) 37 (7)
53 9 19 58 47 36
53 8 16 58 66 20
53 7 22 58 58 23
53 21 (3) 58 54 (5) 36 (8)
(4) (2) (8) (9)
(4) (1) (6) (10)
(2) (4) (5) (8)
(2) (3) (6) (10)
(8) (4) (5) (9)
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Table 5 Difference (Dsolo) between the initial (April 2003) and final (December 2005) amounts of K, in kg ha1, in the soil profile,a as affected by crop rotations and soil management (fall-winter/spring). Depth (cm)
Treataments Sun flower Millet (kg ha1)
0–5 5–10 10–20 20–40 40–60 S(0–60)
0 7 49 40 11 86
(5)b (7) (13) (8) (9) (17)
Triticale Sorghum (kg ha1) 14 20 50 30 20 66
(7) (3) (10) (16) (12) (19)
a
Dsoil = Ksoil initial Ksoil final, where Ksoil initial = 350 kg ha1.
b
Values in parenthesis show the mean standard error.
Sunn hemp (kg ha1) 8 24 48 43 16 92
(6) (7) (10) (13) (23) (16)
inorganic P, and the production of organic anions that compete with phosphate for binding sites that could fix phosphate (Sposito, 1989; Kochhann and Selles, 1991; Andrade et al., 2003; Sousa and Lobato, 2004). High P losses in the soil–plant system (Table 3) were observed under chisel + fallow (36 and 37 kg ha1), which can be explained by the absence of cover crops in the spring, increasing the soil’s susceptibility to the P fixation process. Additionally, even though chiseling is a low-till practice, it may have contributed to increased contact between phosphate ions and soil colloids and, consequently, P fixation (Novais et al., 2007). The triticale/millet treatment also led to a large decrease in P in the soil–plant system during the experiment, but these results may be related to the high amount of millet roots found in this treatment (Calonego and Rosolem, 2010), resulting in greater P storage in radical tissues, which was not considered when calculating the P budget in the system (Eq. (2)). Available K increased in the 0–0.05 m layer in most of the treatments, especially with the triticale/millet rotation. In the triticale/chisel + fallow treatment, K content decreased in this layer and increased in the 0.05–0.10 m layer (Table 5). The K content in upper soil layers can increase over time due to the deposition of fertilizer a few centimeters below the surface, the release of nutrients from plant tissues on the soil surface, decreased nutrient movement to lower layers via leaching, and/ or decreased immobilization and export by plants. Garcia et al. (2008) also found increased K levels in superficial soil layers under NT, and attributed this finding to the cover crops’ ability to recycle nutrients, taking up non-exchangeable K from the soil and then returning the nutrient in available forms through rain washing. Franchini et al. (2003) attributed the K accumulation at the uppermost soil layers in systems with high organic residue inputs to the preference of organic anions for polyvalent cations, which are leached to deeper layers instead of K, and thus increase the percentage of K in the soil CEC of the superficial layers. The chisel + fallow treatments altered soil K dynamics, resulting in a small decrease in available K in the 0.10–0.20 m layer (Table 5). These results could be explained by the absence of cover crops, which could recycle K from deeper soil layers in this region. Furthermore, chiseling resulted in K leaching to deeper layers (Table 5), with an increased available K content being detected in the 0.20–0.40 m layer when sunflowers were grown in the autumn–winter season. A high K movement to the 0.40–0.60 m layer was observed when triticale was grown, although other treatments were also have resulted in some K accumulation in this layer when compared with the initial soil analysis. The absence of plants for a certain period may have contributed to K leaching to greater depths; according to Rosolem et al. (2006a), soil covering can prevent nutrient leaching to deeper layers, in addition to increasing the K content near the soil surface.
Chiseling (kg ha1) 8 12 29 5 20 8
(5) (7) (10) (13) (23) (21)
Millet (kg ha1) 26 22 54 18 31 36
(8) (8) (13) (8) (9) (17)
Sorghum (kg ha1) 14 16 46 30 27 52
(7) (3) (7) (13) (11) (11)
Sunn hemp (kg ha1) 10 22 52 20 28 57
(5) (2) (16) (13) (7) (14)
Chiseling (kg ha1) 5 4 20 19 33 6
(3) (8) (8) (12) (9) (16)
The exchangeable K content decreased in the 0.05–0.60 m layer in all treatments except for triticale/chisel + fallow and sunflower/ chisel + fallow, in which the levels decreased in the 0.10–0.40 m and 0.05–0.20 m layers, respectively. The decreased K content in these layers was due to K absorption by roots, as these are highly root-colonized layers, and also K losses by leaching to deeper layers. This conclusion is supported by the results found in the 0.40–0.60 m layer, where available K was increased (Table 5). Ng Kee Kwong and Deville (1984) observed K losses between 64 and 136 kg ha1 by leaching at depths below 1.00 m in an area cropped to sugarcane and fertilized annually with high K rates. Johnston and Goulding (1992) suggested that approximately 1 kg ha1 of K is lost for every 100 mm of rainwater leached through the soil in a field, but this value may be larger if K is displaced with a solution that contains a higher concentration of Ca2+ ions. Overall, the soil K decreased in the soil profile down to 0.60 m. However, the decreases were lower with chisel + fallow because these treatments lack cover crops and so the nutrient demand was low. Furthermore, soil samples were taken after spring plants were dry, and likely much of the K in the soil–plant system was immobilized by cover crops under the other treatments. Decreased soil K due to extraction by cover crops must not be considered a loss because the nutrient is still stored in plant tissues (Garcia et al., 2008), and will return to the soil with the first rains (Rosolem et al., 2006b). Hence, this temporary unavailability helps in reducing nutrient leaching. The greatest soil K decreases in the profile (from 86 to 92 kg ha1) occurred under sunflower/millet and sunflower/Sunn hemp. For sunflower/millet, this may be due to the fact that the largest K content accumulation occurred in the cover crop plants (77 kg ha1) at the time of soil sampling (Table 6). For the sunflower/Sunn hemp treatment, K extraction by the cover crop (48 kg ha1) was not the main factor decreasing the K content in the soil, so this decrease in K was probably due to losses leaching, given that in calculating the K budget in the soil–plant system (Table 6), there was a 95 kg ha1 deficit in this crop rotation. In the other crop rotations, deficits also occurred in the K budgets of the systems, but in smaller proportions. It is interesting to note that most treatments including triticale showed less K loss, and this species accumulates large amounts of K and has a high potential as a K cycling species (Rosolem et al., 2003). Potassium losses from soil commonly occur via leaching to greater depths, which is influenced by the production system. The K leaching intensity depends on the amount of rain, fertilizer rate, and soil texture (Rosolem et al., 2006a). Additionally, the action of OAs interferes with cation leaching due to the anionic character of OAs, which form stable complexes with cations, especially divalent and trivalent cations, altering the cation leaching order in the soil and thereby diminishing K leaching (Franchini et al., 1999). Thus, the differences found in this experiment can be explained by the
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Table 6 Budget of K (kg ha1) as affected by K inputs and outputs from the soil–plant system in each crop rotations and soil management. K in the soil–plant ystem
Treataments Sun flower
Kfert a Kcc b Kexp c Ksi d Ksf e Budgetg a b c d e f g
Triticale
Millet (kg ha1)
Sorghum (kg ha1)
Sunn hemp (kg ha1)
Chiseling (kg ha1)
Millet (kg ha1)
Sorghum (kg ha1)
Sunn hemp (kg ha1)
Chiseling (kg ha1)
100 77 59 350 264 50
100 53 53 350 284 60
100 48 48 350 258 95
100 – 67 (3) 350 342 (17) 41 (15)
100 46 58 350 314 32
100 37 52 350 298 62
100 31 72 350 292 54
100 – 69 (3) 350 344 (19) 37 (14)
(8)f (5) (20) (15)
(16) (5) (19) (18)
(12) (8) (17) (16)
(18) (11) (14) (13)
(11) (8) (13) (11)
(11) (10) (20) (13)
K added as fertilizer (accumulated over two years). K accumulated in cover crop shoots. K exported by grains (accumulated over three years). Initial exchangeable K in the soil profile (0–60 cm). Final exchangeable K in the soil profile after three years (0–60 cm). Values in parenthesis show the mean standard error. Budget = ((Kfert + Ksi)–(Kexp + Kcc) Ksf).
fact that OA persistence and the organic anions added to the soil are dependent on the management system and cultivated species (Pavinato and Rosolem, 2008). Considering the P and K inputs and outputs of the investigated soil–plant systems, it is clear that nutrient losses occurred in all of the management systems. The observed P losses varied between 15% and 33% (Table 4), and K losses varied between 7% and 21% (Table 6) compared with the original levels in the soil profile plus the amount of fertilizer applied. 4. Conclusions The soil profile is most depleted in P and K in 0.10–0.20 m layer irrespective of crop rotation and soil management system,. The soil–plant system P loss is bigger than the amount exported by soybean grains, showing that the system is not avoiding completely P fixation by the soil. For K, generally less than 50% of the applied fertilizer was found in the soil–plant system, showing that considerable amounts of the nutrient were leached below 0.60 m in the soil profile. However, chiseling/fallow (in spring) is effective in decreasing this loss, although there is no nutrient stored in plant tissue as occurs in the treatments with cover crops during this period. Among the crop rotations, the use of high K accumulating plants as triticale maintained the nutrient in the soil–plant system, avoiding K losses by leaching. Therefore, management systems and crop rotations affect P and K dynamics and losses in soil, and special attention should be paid to the management of fertilizers in these systems in order to minimize P fixation and K leaching and prevent soil depletion. Acknowledgments This research was funded by FAPESP (The State of Sa˜o Paulo Research Foundation) and CNPq (The National Council for Scientific and Technological Development). References Aguilar, A.Y., Van Diest, A., 1981. Rock phosphate mobilization induced by the alkaline uptake pattern of legumes utilizing symbiotically fixed nitrogen. Plant and Soil 61, 27–41. Andrade, F.V., Mendonc¸a, E.S., Alvarez, V.V.H., Novais, R.F., 2003. Adic¸a˜o de a´cidos orgaˆnicos e hu´micos em Latossolos e adsorc¸a˜o de fosfato. Revista Brasileira de Cieˆncia do Solo 27, 1003–1011. Bo¨hm, W., 1979. Methods of Studying Root System. Springer-Verlag, Berlin. Borkert, C.M., Gaudeˆncio, C.D.A., Pereira, J.E., Pereira, L.R., Oliveira Junior, A. de O., 2003. Nutrientes minerais na biomassa da parte ae´rea em culturas de cobertura de solo. Pesquisa Agropecua´ria Brasileira 38, 143–153.
Calonego, J.C., Rosolem, C.A., Foloni, J.S.S., 2005. Lixiviac¸a˜o de pota´ssio da palha de plantas de cobertura em diferentes esta´dios de senesceˆncia apo´s a dessecac¸a˜o quı´mica. Revista Brasileira de Cieˆncia do Solo 29, 99–108. Calonego, J.C., Rosolem, C.A., 2010. Soybean root growth and yield in rotation with cover crops under chiseling and no-till. European Journal of Agronomy 33, 242–249. Carpim, L.K., Assis, R.L., de, A.J.B.P., Braz, Silva, G.P., Pires, F.R., Pereira, V.C., Gomes, G.V., Silva, A.G.da, 2008. Liberac¸a˜o de nutrientes pela palhada de milheto em diferentes esta´dios fenolo´gicos. Revista Brasileira de Cieˆncia do Solo 32, 2813–2819. De-Maria, I.C., Castro, O.M.de, 1993. Fo´sforo, pota´ssio e mate´ria orgaˆnica em um Latossolo Roxo, sob sistemas de manejo com milho e soja. Revista Brasileira de Cieˆncia do Solo 17, 471–477. Encide-Olibone, A.P., Olibone, D., Rosolem, C.A., 2008. Atividade radicular da soja: definic¸a˜o de um me´todo. Revista Brasileira de Cieˆncia do Solo 32, 899–903. Foloni, J.S.S., Rosolem, C.A., 2008. Produtividade e acu´mulo de pota´ssio na soja em func¸a˜o da antecipac¸a˜o da adubac¸a˜o pota´ssica no sistema plantio direto. Revista Brasileira de Cieˆncia do Solo 32, 1549–1561. Foloni, J.S.S., Tiritan, C.S., Calonego, J.C., Alves Junior, J., 2008. Aplicac¸a˜o de fosfato natural e reciclagem de fo´sforo por milheto, braquia´ria, milho e soja. R Bras. Ci. Solo 32, 1147–1155. Franchini, J.C., Hoffmann-Campo, C.B., Torres, E., Miyazawa, M., Pavan, A., 2003. Organic composition of green manure during growth and its effect on cation mobilization in an acid Oxisol. Communications in Soil Science and Plant Analysis 34, 2045–2058. Franchini, J.C., Miyazawa, M., Pavan, M.A., Malavolta, E., 1999. Dinaˆmica de ı´ons em solo a´cido lixiviado com extratos de resı´duos de adubos verdes e soluc¸o˜es puras de a´cidos orgaˆnicos. Pesquisa Agropecua´ria Brasileira 34, 2267–2276. Garcia, R.A., Crusciol, C.A.C., Calonego, J.C., Rosolem, C.A., 2008. Potassium cycling in a corn–brachiaria cropping system. European Journal of Agronomy 28, 579–585. Johnston, A.E., Goulding, K.W.T., 1992. Potassium in Ecosystems, Biogeochemical Fluxes of Cations in Agro-and Forest-Systems. International Potash Institute, Basel. Kochhann, R.A., Selles, F., 1991. O solo e o sistema de manejo conservacionista. In: Fernandes, J.M., Fernandez, M.R., Kochhann, R.A., Selles, F., Zentner, R.P. (Eds.), Manual de manejo conservacionista do solo para os estados do Rio Grande do Sul, Santa Catarina e Parana´. CIDA/Embrapa-CNPT, Passo Fundo. Kulmatiski, A., Beard, K.H., Verweij, R.J.T., February, E.C., 2010. A depth-controlled tracer technique measures vertical, horizontal and temporal patterns of water use by trees and grasses in a subtropical savanna. New Phytologist 188 (1), 188–199. Malavolta, E.A., Vitti, G.C., Oliveira, S.A., 1997. Avaliac¸a˜o do estado nutricional das plantas: princı´pios e aplicac¸o˜es. Potafo´s, Piracicaba. Mengel, K., Kirkby, E.A., 1987. Principles of Plant Nutrition, 4th ed. International Potash Institute, Bern. Ng Kee Kwong, K.F., Deville, J., 1984. Nitrogen leaching from soils cropped with sugarcane under the humid tropical climate of Mauritius, Indian Ocean. Journal of Environment Quality 13, 471–474. Novais, R.F., Smyth, T.J., Nunes, F.N., 2007. Fo´sforo. In: Novais, R.F., Alvarez, V.H., Barros, N.F., Fontes, R.L.F., Cantarutti, R.B., Neves, J.C.L. (Eds.), Fertilidade do solo. Sociedade Brasileira de Cieˆncia de Solo, Vic¸osa. Pavinato, P.S., Rosolem, C.A., 2008. Disponibilidade de nutrientes no solo – decomposic¸a˜o e liberac¸a˜o de compostos orgaˆnicos de resı´duos vegetais. Revista Brasileira de Cieˆncia do Solo 32, 911–920. Pivetta, L.A., Castoldi, G., Santos, G.P., Rosolem, C.A., 2011. Crescimento e atividade de raı´zes de soja em func¸a˜o do sistema de produc¸a˜o. Pesquisa Agropecua´ria Brasileira 46, 1547–1554. Raij, B., van Andrade, J.C., Cantarella, H., Quaggio, J.A., 2001. Ana´lise quı´mica para avaliac¸a˜o da fertilidade de solos tropicais. Instituto Agronoˆmico, Campinas.
C.A. Rosolem, J.C. Calonego / Soil & Tillage Research 126 (2013) 127–133 Rosolem, C.A., Calonego, J.C., Foloni, J.S.S., 2003. Lixiviac¸a˜o de pota´ssio da palha de coberturas de solo em func¸a˜o da quantidade de chuva recebida. Revista Brasileira de Cieˆncia do Solo 27, 355–362. Rosolem, C.A., Calonego, J.C., Foloni, J.S.S., Garcia, R.A., 2007. Pota´ssio lixiviado da palha de aveia-preta e milheto apo´s a dessecac¸a˜o quı´mica. Pesquisa Agropecua´ria Brasileira 42, 1169–1175. Rosolem, C.A., Garcia, R.A., Foloni, J.S.S., Calonego, J.C., 2006a. Lixiviac¸a˜o de pota´ssio no solo de acordo com suas doses aplicadas sobre palha de milheto. Revista Brasileira de Cieˆncia do Solo 30, 813–819. Rosolem, C.A., Santos, F.P., Foloni, J.S.S., Calonego, J.C., 2006b. Pota´ssio no solo em consequ¨eˆncia da adubac¸a˜o sobre a palha de milheto e chuva simulada. Pesquisa Agropecua´ria Brasileira 41, 1033–1040. Smith, K.A., Mullins, C.E., 1991. Soil analysis: Physical Methods. Marcel Dekker, Inc., New York.
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Phosphorus and potassium budget in the soil–plant system in crop rotations under no-till C.A. Rosolem *, J.C. Calonego Department of Crop Science, College of Agricultural Sciences, Sa˜o Paulo State University, Botucatu, SP, Brazil
A R T I C L E I N F O
A B S T R A C T
Article history: Received 12 March 2012 Received in revised form 2 August 2012 Accepted 4 August 2012
Soil management and crop rotations can affect P and K budget in soil, decreasing losses, and increasing fertilizer use efficiency. The P and K budget in the soil–plant system at depths up to 60 cm was studied for different soil managements and crop rotations under no-till for three years in Botucatu, Sa˜o Paulo, Brazil. The investigated crop rotations were: triticale (X Triticosecale) and sunflower (Helianthus annuus) cropped in autumn–winter; pearl millet (Pennisetum glaucum), forage sorghum (Sorghum bicolor), and Sunn hemp (Crotalaria juncea) were grown in the spring, as well as an additional treatment with chiseling followed by a fallow period; and soybean (Glycini max, L., Merril) was cropped in the summer. Each year triticale and sunflower were grown in plots and pearl millet, forage sorghum, Sunn hemp and of chisel/ fallow in sub-plots. The triticale/millet rotation led to the largest decrease in available P within the 0– 0.60 m layer of the soil profile and the largest K increase within the 0–0.05 m layer. Potassium mobility in the soil profile and the increases in the available K content in the 0.40–0.60 m layer were independent of the management system. Crop rotations with or without chiseling are not effective in preventing soil P losses. There is considerable K leaching below 0.60 m, but chiseling and the use of high K accumulating plants as triticale results in lower K losses. ß 2012 Elsevier B.V. All rights reserved.
Keywords: Cover crops Management soil Nutrient cycling
1. Introduction Nutrients in soil solution can be taken up by plants, leached, lost to the atmosphere, or transformed into non-labile forms. The fate of nutrients available in the soil depends on root access, plant demand, exports via harvesting, and soil physical, chemical and mineralogical conditions. In highly weathered tropical soils, with predominance of 1:1 clay minerals and sesquioxides, phosphorus (P) availability is low because most of it is in non-labile forms, while potassium (K) availability may be decreased via leaching (Novais et al., 2007). An adequate soil management and crop rotations can reduce these losses and increase fertilizer use efficiency by increasing nutrient storage in the soil–plant system (Sousa and Lobato, 2004), and promoting nutrient recycling (Foloni and Rosolem, 2008; Foloni et al., 2008; Garcia et al., 2008). Crop residues deposited on the soil surface in areas under no-till (NT) provide considerable nutrient reserves (Carpim et al., 2008). Thus, crop residues that remain on the soil surface, in addition to protecting against climatic effects and erosion, are mineralized, releasing nutrients that can be used by future crops (Borkert et al., 2003). Some nutrients, such as K, can be washed directly to the soil
Abbreviations: NT, no-till; AO, organic acid. * Corresponding author. Tel.: +55 18 3880 7161; fax: +55 14 3880 7000. E-mail address: [email protected] (C.A. Rosolem). 0167-1987/$ – see front matter ß 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.still.2012.08.003
via rainfall, independent of the degree of organic matter mineralization (Rosolem et al., 2003, 2007; Calonego et al., 2005). According to a review by Pavinato and Rosolem (2008), adding plant material to soil also causes rapid increases in organic acid (OA) concentrations, which occur through organic matter decomposition, direct leaf run-off, and root and microbial exudates production. Due to their anionic character, these OAs interact with the soil solid phase and occupy P adsorption sites. In addition, they can form stable complexes with aluminum (Al) and iron (Fe) that prevent these metals from reacting with P (Sposito, 1989). Thus, under NT, the straw left on the soil surface may play an important role in reducing P fixation in the soil, increasing phosphate fertilization efficiency and affecting P balance in the system. According to Franchini et al. (1999), these organic compounds also increase the percentages of calcium (Ca), magnesium (Mg), and K in the soil cation exchange capacity (CEC) due to the complexation of Al ions, which can reduce nutrient losses due to leaching, especially K. However, according to Pavinato and Rosolem (2008), the efficiency of OAs in increasing soil nutrient availability depends on factors such as the type and persistence of these compounds, which are controlled by the management system and cultivated species. Hence the crop rotation my also affect the nutrient balance in the system. In NT systems, cover crop rotations (or green manure) are intended to not only protect the soil surface but also to improve its physical, chemical, and biological attributes, even at deeper
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depths, through the effect of roots. This improved soil profile may increase the efficiency of water and fertilizer use, and distinct crop rotations, by exploring different soil regions or layers, can contribute to avoid leaching, balance the soil nutrients, increase fertility, and improve mineral fertilizer use. Crop rotations play an important role in nutrient recycling because plant species vary in their abilities to produce biomass, absorb ions efficiently, and exploit nutrients at different soil depths (Mengel and Kirkby, 1987). Each of these characteristics should be considered in fertilizer management program. The objective of this study were to evaluate the P and K budget in the soil profile at depths down to 0.60 m as affected by soil management systems and crop rotations. 2. Materials and methods 2.1. Experimental site and treatments An experiment was conducted in Botucatu, Sa˜o Paulo, Brazil, 228490 S, 488250 W and 786 m altitude, for three years on a Typic Rhodudalf (Soil Survey Staff, 2006), clay, with depth greater than 2 m and with 60% to 79% of kaolinite and 13% to 20% of gibbsite. Before this experiment, the area had been under NT for 6 years, with a soybean/black oats/corn/triticale rotation. The climate, according to Ko¨ppen classification is CWa, that is, a subtropical humid climate with dry winter. The dry season is well-defined between May and September. The mean rainfall average is approximately 1400 mm, the highest monthly mean temperature is over 22 8C and the lowest is below 18 8C (Fig. 1). Before starting the experiment, the soil was sampled for chemical (Raij et al., 2001) and physical analyses (Smith and Mullins, 1991) down to 0.60 m (Table 1). Treatments consisted of cropping triticale (X Triticosecale Wittmack) and sunflower (Helianthus annuus) in the fall-winter (May to August in the three years), followed by pearl millet (Pennisetum glaucum L.), forage sorghum (Sorghum bicolor (L.) Moench) or Sunn hemp (Crotalaria juncea L.) cropped in the spring (October and November in the three years), plus an additional treatment that was chiseled (in September of the first year) and kept fallow during the springs. Soybean (Glycine max L.,Merril) was cropped in the summer (December through April in the three years) in all the plots. Details of the rotations are presented in Table 2. The experimental design was a split-plot in complete
randomized blocks, with four replications. Triticale and sunflower were grown in the plots in the fall/winter with pearl millet, sorghum, Sunn hemp, and chiseling/falow in sub-plots. Plots were 8.0 m 32.0 m, and sub-plots were 8.0 m 5.0 m, with 4.0 m between blocks, plots and sub-plots. Soybean and sunflower were planted in rows 0.45 m apart from each other. The other crops were planted at a spacing of 0.17 m between rows. The chisel plow had seven shanks mounted on two parallel bars on a square tool carrier. The shanks, inclined 258 forward, were set 0.60 m apart resulting in an effective between-shank spacing of 0.30 m, with a maximum operating depth of 0.30 m. A clodbreaking roller was attached to break the biggest clods, decrease surface roughness and avoid disking. The soil was chiseled only once, after the fall-winter crops in the first year, and the chiseled plots were left fallow between the winter and summer crops thereafter. In fallow plots the weeds were hoed as required. Each year soybean received no N, 26.5 kg ha1 of P and 50 kg ha1 of K as triple superphosphate and potassium chloride, and pearl millet and sorghum received 40 kg ha1 of N as urea at planting. Sunflower and triticale received no fertilizers. Triticale and sunflower grains were not harvested because the yields were very low; hence, the plants were left to naturally lodge. Pearl millet, sorghum and Sunn hemp were desiccated with ghyphosate at 57, 50 and 62 days after plant emergence, respectively in the first, second and third years. 2.2. Sample collection and analysis In December of the last year of the experiment, immediately before soybean planting, pearl millet, forage sorghum and Sunn hemp were sampled, using 0.25 m 0.25 m wooden frames. Five sub-samples were randomly taken from each subplot and combined in one. This material was oven dried at 65 8C for three days to determine dry matter yield. A subsample was ground for P and K analysis (Malavolta et al., 1997) and the rest of the material was returned to the respective plots. Using the dry matter and nutrient concentrations, the amount of P and K in the remains of plant residues on soil surface at soybean planting was calculated. At the same time, soil was sampled at depths from 0 to 0.05, 0.05 to 0.10, 0.10 to 0.20, 0.20 to 0.40 and 0.40 to 0.60 m. Three subsamples were taken per subplot and combined in one, air dried, passed through a 2 mm sieve and analyzed for available P (resin) and exchangeable K according to Raij et al. (2001). The mass
Fig. 1. Rainfall and temperature (monthly average) during April 2003 and December 2005. Vertical arrows show when operations were realized.
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Table 1 Selected chemical and physical properties of the soil at the beginning of the experiment. Chemical properties Depth (m)
pHCaCl2
OM (g dm3)
Presin (mg dm3)
H + Al (mmolc dm3)
K (mmolc dm3)
Ca (mmolc dm3)
Mg (mmolc dm3)
CEC (mmolc dm3)
0–0.05 0.05–0.10 0.10–0.20 0.20–0.40 0.40–0.60
5.4 4.6 4.6 4.8 5.1
32 27 26 22 22
37 26 15 3 2
56 91 97 69 63
4.7 3.0 2.5 1.1 0.2
37 28 35 46 57
16 11 16 15 11
114 134 150 131 132
Physical properties Depth (m)
0–0.05 0.05–0.10 0.10–0.20 0.20–0.40 0.40–0.60
SPRa (MPa)
1.4 2.8 2.3 2.3 1.8
Soil moistureb (g g1)
0.29 0.29 0.34 0.38 0.42
Bulk density (g cm3)
1.22 1.39 1.38 1.29 1.31
Porosity Total (m3 m3)
Macro (m3 m3)
Micro (m3 m3)
0.57 0.53 0.52 0.50 0.58
0.11 0.08 0.07 0.05 0.05
0.42 0.42 0.45 0.45 0.48
Textural properties Depth (m)
Sand (g kg1)
Clay (g kg1)
Silt (g kg1)
0–0.05 0.05–0.10 0.10–0.20 0.20–0.40 0.40–0.60
137 131 128 110 88
571 598 599 645 715
292 272 273 245 197
a b
SPR, soil penetration resistance. Soil water content at the time penetration resistance was measured (April 2003).
of available P and K were calculated considering their concentrations, soil bulk density and soil volume. Considering soil P and K available in April of the first year and after three years, equation 1 was used to estimate the variation in soil P and K mass in each soil layer (down to 0.60 m):
difference between total inputs and utilization. Results greater and smaller than zero were considered as ‘‘gains’’ or ‘‘losses’’ in the soil–plant system, respectively, down to 0.60 m in the soil profile, which were estimated using Eq. (2): Budget ¼ ððNfert þ Nsi Þ ðNexp þ Ncc ÞÞ Nsf
Dsoil ¼ N soil initial Nsoil final
where Dsoil is the variation in available P and K in the soil profile down to 0.60 m, between April of the first year and December of the last year of the experiment; Nsoil initial is the P and K available in the soil profile in April of the first year; Nsoil final is the P and K available in the soil profile in December of the last year. In the P and K budget in the soil–plant system were considered the exports by soybean grown in the first and second year of the experiment. Nutrient exports were estimated using the grain yields and P and K concentrations in the grain, determined as in Malavolta et al. (1997). To calculate P and K budget in the soil–plant system, initial available P and K in the soil down to 0.60 m were added to the fertilizer applied (53 and 100 kg ha1, respectively), and this was taken as inputs. The quantities exported with the soybean grains (two harvests) plus the amount present in the above ground material in December of the last year of the experiment were considered as ‘‘utilized’’ by plants. The P and K residual (final) amount in the soil down to 0.60 m was subtracted from the Table 2 Crop rotations and treatments. Summer
Fall/winter (plots)
Spring (sub-plots)
Soybean
Triticale
Pearl millet Forage sorghum Sun hemp Chiseling/fallow Pearl millet Forage sorghum Sun hemp Chisel/fallow
Sunflower
(2)
(1) where Budget is the diference in P and K amount in the system between April of the first and December of the last year; Nfert is P or K in the fertilizer applied; Ncc is P or K accumulated in the cover crops; Nexp is P and K exported by soybean; Nsi is the initial; and Nsf is the final available P and K in the soil profile down to 0.60 m. 2.3. Statistical analysis In spite of the original split-plot design, all data were collected randomly, and descriptive statistics was applied, and the mean standard errors were calculated and used to compare the results. 3. Results and discussion The available P content in the topsoil increased after 3 years, with the exception of the triticale/millet and triticale/Sunn hemp rotations, in which P decreased within the 0–0.05 m and 0.05– 0.10 m layers, respectively. There were no variations in P content in the 0.05–0.10 m layers of the triticale/millet and triticale/ chisel + fallow rotations (Table 3). These results cannot be explained by P accumulation in the cover crops at the time of soil sampling because systems involving chiseling + fallow also resulted in increased P at the soil surface. Considering that the same amount of fertilizer was added to all rotations, and the amount of P exported by soybeans did not vary much (Table 4), the higher available P content in the surface soil layers indicates that system losses were reduced. In this case, the increase may be due to decreased P fixation or solubilization of less labile P forms in the soil (Andrade et al., 2003; Sposito, 1989). Growing Sunn hemp, generally a species with small root system (Calonego and Rosolem, 2010), resulted in the largest increase in the available P content in
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Table 3 Difference (Dsoil) between the initial (April 2003) and final (December 2005) amounts of P, in kg ha1, in the soil profile,a as affected by crop rotations and soil management (fall-winter/spring). Depth (m)
Treatments Sun flower
Triticale
Millet (kg ha1) 0–0.05 0.05–0.10 0.10–0.20 0.20–0.40 0.40–0.60 S(0–60)
6 2 5 3 0 0
Sorghum (kg ha1)
(3)b (5) (6) (1) (1) (7)
2 5 8 3 0 4
Sunn hemp (kg ha1)
(4) (4) (3) (1) (1) (8)
11 5 7 3 1 5
a
Dsoil = Psoil initial Psoil final, where Psoil initial = 58 kg ha1.
b
Values in parenthesis show the mean standard error.
Chiseling (kg ha1)
(4) (3) (3) (1) (2) (6)
2 5 7 2 1 3
the surface layer. Furthermore, decreased P content was observed in the 0–0.05 m layer in the triticale/millet system, coinciding with increased root production (Calonego and Rosolem, 2010). Therefore, differences in P accumulation in the roots at the time of soil sampling may have affected the resulting soil P contents. More Psolubilizing bacteria are present in legumes than in grasses (Sylvester-Bradley et al., 1982), and as the P content in plant tissues depends on mineralization for the nutrient to become available (Teixeira et al., 2009), Sunn hemp, a legume presenting a low C/N ratio, may have released more P back into the soil compared with the grasses. In addition, N fixing legumes take up more cationic than anionic nutrients, resulting in rizosphere acidification and increased P availability (Aguilar and Van Diest, 1981). However, De-Maria and Castro (1993) observed a higher P content in soil cropped to black oat compared with Sunn hemp after seven years of an annual crop rotation, which would have allowed time for root mineralization and thus increased the P content in the soil. Therefore, differences in P behavior in the soil profile under different crop rotation management systems can be attributed to the effects on P fixation, solubilization of less labile forms, and P accumulation by undecomposed roots. In the 0.10–0.20 m soil layer, the amount of available P decreased, probably because root activity is high at this depth. Studies to determine the presence of active roots throughout the soil profile by indirect methods (Bo¨hm, 1979; Encide-Olibone et al., 2008) show that root activity of grasses, forest species, and soybeans can reach 30% at a depth of 0.20 m (Kulmatiski et al., 2010; Pivetta et al., 2011) and 90% at a depth of 0.10 m (Pivetta et al., 2011). Thus, as P additions occur in the topsoil and the nutrient mobility low, the result is a P depletion in the 0.10–0.20 m
(2) (4) (3) (1) (1) (4.8)
Millet (kg ha1)
Sorghum (kg ha1)
2 0 8 1 0 11
10 8 7 3 0 8
(3) (4) (3) (2) (2) (5)
(3) (5) (4) (1) (1) (6)
Sunn hemp (kg ha1) 8 3 6 0 1 0
(5) (3) (3) (1) (1) (5)
Chiseling (kg ha1) 7 0 8 2 1 4
(4) (4) (2) (2) (1) (5)
soil layer and an accumulation in the 0–0.10 m layer under some crop rotations. The available P content in the soil profile decreased under sunflower/sorghum, sunflower/chisel + fallow, triticale/millet, and triticale/chisel + fallow rotations and increased under the sunflower/Sunn hemp and triticale/sorghum. The 3-year consecutive succession of triticale/millet promoted the greatest P deficit in the soil profile, decreasing the available P by 11 kg ha1, whereas growing triticale/sorghum resulted in the greatest P increase in the profile, increasing its availability by 8 kg ha1 (Table 3). The greatest P decrease in the 0–0.60 m layer, in the triticale/millet treatment, was more affected by the decrease in available P than by the increased exportation or immobilization by the cover crops (Table 4). However, in a study by Foloni et al. (2008), millet exhibited the highest P accumulation in plant tissues, which led to a greater decrease in the soil available P and so to a less prone P fixation. The increased P availability in the soil profiles under triticale/sorghum and sunflower/Sunn hemp (Table 3) is related to the greater available P content observed in the final evaluation, given that the cover crops did not accumulate considerable amounts of P and that P export by soybeans was similar between treatments (Table 4). Overall, after 3 years of crop rotations, the P content decreased in the system by amounts ranging from 17 to 37 kg ha1 (Table 4). Part of this decrease can probably be attributed to the P fixation process, which makes P unavailable to plants. The differences in the amounts of P lost from the soil–plant system across treatments are related to differences between the plants, such as their ability to solubilize P (transforming it into an organic form), the intensity of soil tillage, the occurrence of microbial activity able to solubilize
Table 4 Budget of P (kg ha1) in the soil plant system as affected by P inputs and outputs from the soil–plant system in each crop rotations and soil management. P in the soil–plant system
Treataments Sun flower
Triticale 1
Millet (kg ha Pfert a Pcc b Pexp c Psi d Psf e Budgetg a b c d e f g
53 17 18 58 58 17
)
(3)f (2) (7) (9)
P added as fertilizer (accumulated over two years). P accumulated in cover crop shoots. P exported by grains (accumulated over two years). Initial available P in the soil profile (0–60 cm). Final available P in the soil profile (0–60 cm). Values in parenthesis show the mean standard error. Budget = ((Pfert + Psi) (Pexp + Pcc) Psf)
Sorghum (kg ha1)
Sunn hemp (kg ha1)
Chiseling (kg ha1)
Millet (kg ha1)
Sorghum (kg ha1)
Sunn hemp (kg ha1)
Chiseling (kg ha1)
53 11 16 58 54 30
53 8 17 58 63 22
53 19 (2) 58 55 (5) 37 (7)
53 9 19 58 47 36
53 8 16 58 66 20
53 7 22 58 58 23
53 21 (3) 58 54 (5) 36 (8)
(4) (2) (8) (9)
(4) (1) (6) (10)
(2) (4) (5) (8)
(2) (3) (6) (10)
(8) (4) (5) (9)
C.A. Rosolem, J.C. Calonego / Soil & Tillage Research 126 (2013) 127–133
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Table 5 Difference (Dsolo) between the initial (April 2003) and final (December 2005) amounts of K, in kg ha1, in the soil profile,a as affected by crop rotations and soil management (fall-winter/spring). Depth (cm)
Treataments Sun flower Millet (kg ha1)
0–5 5–10 10–20 20–40 40–60 S(0–60)
0 7 49 40 11 86
(5)b (7) (13) (8) (9) (17)
Triticale Sorghum (kg ha1) 14 20 50 30 20 66
(7) (3) (10) (16) (12) (19)
a
Dsoil = Ksoil initial Ksoil final, where Ksoil initial = 350 kg ha1.
b
Values in parenthesis show the mean standard error.
Sunn hemp (kg ha1) 8 24 48 43 16 92
(6) (7) (10) (13) (23) (16)
inorganic P, and the production of organic anions that compete with phosphate for binding sites that could fix phosphate (Sposito, 1989; Kochhann and Selles, 1991; Andrade et al., 2003; Sousa and Lobato, 2004). High P losses in the soil–plant system (Table 3) were observed under chisel + fallow (36 and 37 kg ha1), which can be explained by the absence of cover crops in the spring, increasing the soil’s susceptibility to the P fixation process. Additionally, even though chiseling is a low-till practice, it may have contributed to increased contact between phosphate ions and soil colloids and, consequently, P fixation (Novais et al., 2007). The triticale/millet treatment also led to a large decrease in P in the soil–plant system during the experiment, but these results may be related to the high amount of millet roots found in this treatment (Calonego and Rosolem, 2010), resulting in greater P storage in radical tissues, which was not considered when calculating the P budget in the system (Eq. (2)). Available K increased in the 0–0.05 m layer in most of the treatments, especially with the triticale/millet rotation. In the triticale/chisel + fallow treatment, K content decreased in this layer and increased in the 0.05–0.10 m layer (Table 5). The K content in upper soil layers can increase over time due to the deposition of fertilizer a few centimeters below the surface, the release of nutrients from plant tissues on the soil surface, decreased nutrient movement to lower layers via leaching, and/ or decreased immobilization and export by plants. Garcia et al. (2008) also found increased K levels in superficial soil layers under NT, and attributed this finding to the cover crops’ ability to recycle nutrients, taking up non-exchangeable K from the soil and then returning the nutrient in available forms through rain washing. Franchini et al. (2003) attributed the K accumulation at the uppermost soil layers in systems with high organic residue inputs to the preference of organic anions for polyvalent cations, which are leached to deeper layers instead of K, and thus increase the percentage of K in the soil CEC of the superficial layers. The chisel + fallow treatments altered soil K dynamics, resulting in a small decrease in available K in the 0.10–0.20 m layer (Table 5). These results could be explained by the absence of cover crops, which could recycle K from deeper soil layers in this region. Furthermore, chiseling resulted in K leaching to deeper layers (Table 5), with an increased available K content being detected in the 0.20–0.40 m layer when sunflowers were grown in the autumn–winter season. A high K movement to the 0.40–0.60 m layer was observed when triticale was grown, although other treatments were also have resulted in some K accumulation in this layer when compared with the initial soil analysis. The absence of plants for a certain period may have contributed to K leaching to greater depths; according to Rosolem et al. (2006a), soil covering can prevent nutrient leaching to deeper layers, in addition to increasing the K content near the soil surface.
Chiseling (kg ha1) 8 12 29 5 20 8
(5) (7) (10) (13) (23) (21)
Millet (kg ha1) 26 22 54 18 31 36
(8) (8) (13) (8) (9) (17)
Sorghum (kg ha1) 14 16 46 30 27 52
(7) (3) (7) (13) (11) (11)
Sunn hemp (kg ha1) 10 22 52 20 28 57
(5) (2) (16) (13) (7) (14)
Chiseling (kg ha1) 5 4 20 19 33 6
(3) (8) (8) (12) (9) (16)
The exchangeable K content decreased in the 0.05–0.60 m layer in all treatments except for triticale/chisel + fallow and sunflower/ chisel + fallow, in which the levels decreased in the 0.10–0.40 m and 0.05–0.20 m layers, respectively. The decreased K content in these layers was due to K absorption by roots, as these are highly root-colonized layers, and also K losses by leaching to deeper layers. This conclusion is supported by the results found in the 0.40–0.60 m layer, where available K was increased (Table 5). Ng Kee Kwong and Deville (1984) observed K losses between 64 and 136 kg ha1 by leaching at depths below 1.00 m in an area cropped to sugarcane and fertilized annually with high K rates. Johnston and Goulding (1992) suggested that approximately 1 kg ha1 of K is lost for every 100 mm of rainwater leached through the soil in a field, but this value may be larger if K is displaced with a solution that contains a higher concentration of Ca2+ ions. Overall, the soil K decreased in the soil profile down to 0.60 m. However, the decreases were lower with chisel + fallow because these treatments lack cover crops and so the nutrient demand was low. Furthermore, soil samples were taken after spring plants were dry, and likely much of the K in the soil–plant system was immobilized by cover crops under the other treatments. Decreased soil K due to extraction by cover crops must not be considered a loss because the nutrient is still stored in plant tissues (Garcia et al., 2008), and will return to the soil with the first rains (Rosolem et al., 2006b). Hence, this temporary unavailability helps in reducing nutrient leaching. The greatest soil K decreases in the profile (from 86 to 92 kg ha1) occurred under sunflower/millet and sunflower/Sunn hemp. For sunflower/millet, this may be due to the fact that the largest K content accumulation occurred in the cover crop plants (77 kg ha1) at the time of soil sampling (Table 6). For the sunflower/Sunn hemp treatment, K extraction by the cover crop (48 kg ha1) was not the main factor decreasing the K content in the soil, so this decrease in K was probably due to losses leaching, given that in calculating the K budget in the soil–plant system (Table 6), there was a 95 kg ha1 deficit in this crop rotation. In the other crop rotations, deficits also occurred in the K budgets of the systems, but in smaller proportions. It is interesting to note that most treatments including triticale showed less K loss, and this species accumulates large amounts of K and has a high potential as a K cycling species (Rosolem et al., 2003). Potassium losses from soil commonly occur via leaching to greater depths, which is influenced by the production system. The K leaching intensity depends on the amount of rain, fertilizer rate, and soil texture (Rosolem et al., 2006a). Additionally, the action of OAs interferes with cation leaching due to the anionic character of OAs, which form stable complexes with cations, especially divalent and trivalent cations, altering the cation leaching order in the soil and thereby diminishing K leaching (Franchini et al., 1999). Thus, the differences found in this experiment can be explained by the
C.A. Rosolem, J.C. Calonego / Soil & Tillage Research 126 (2013) 127–133
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Table 6 Budget of K (kg ha1) as affected by K inputs and outputs from the soil–plant system in each crop rotations and soil management. K in the soil–plant ystem
Treataments Sun flower
Kfert a Kcc b Kexp c Ksi d Ksf e Budgetg a b c d e f g
Triticale
Millet (kg ha1)
Sorghum (kg ha1)
Sunn hemp (kg ha1)
Chiseling (kg ha1)
Millet (kg ha1)
Sorghum (kg ha1)
Sunn hemp (kg ha1)
Chiseling (kg ha1)
100 77 59 350 264 50
100 53 53 350 284 60
100 48 48 350 258 95
100 – 67 (3) 350 342 (17) 41 (15)
100 46 58 350 314 32
100 37 52 350 298 62
100 31 72 350 292 54
100 – 69 (3) 350 344 (19) 37 (14)
(8)f (5) (20) (15)
(16) (5) (19) (18)
(12) (8) (17) (16)
(18) (11) (14) (13)
(11) (8) (13) (11)
(11) (10) (20) (13)
K added as fertilizer (accumulated over two years). K accumulated in cover crop shoots. K exported by grains (accumulated over three years). Initial exchangeable K in the soil profile (0–60 cm). Final exchangeable K in the soil profile after three years (0–60 cm). Values in parenthesis show the mean standard error. Budget = ((Kfert + Ksi)–(Kexp + Kcc) Ksf).
fact that OA persistence and the organic anions added to the soil are dependent on the management system and cultivated species (Pavinato and Rosolem, 2008). Considering the P and K inputs and outputs of the investigated soil–plant systems, it is clear that nutrient losses occurred in all of the management systems. The observed P losses varied between 15% and 33% (Table 4), and K losses varied between 7% and 21% (Table 6) compared with the original levels in the soil profile plus the amount of fertilizer applied. 4. Conclusions The soil profile is most depleted in P and K in 0.10–0.20 m layer irrespective of crop rotation and soil management system,. The soil–plant system P loss is bigger than the amount exported by soybean grains, showing that the system is not avoiding completely P fixation by the soil. For K, generally less than 50% of the applied fertilizer was found in the soil–plant system, showing that considerable amounts of the nutrient were leached below 0.60 m in the soil profile. However, chiseling/fallow (in spring) is effective in decreasing this loss, although there is no nutrient stored in plant tissue as occurs in the treatments with cover crops during this period. Among the crop rotations, the use of high K accumulating plants as triticale maintained the nutrient in the soil–plant system, avoiding K losses by leaching. Therefore, management systems and crop rotations affect P and K dynamics and losses in soil, and special attention should be paid to the management of fertilizers in these systems in order to minimize P fixation and K leaching and prevent soil depletion. Acknowledgments This research was funded by FAPESP (The State of Sa˜o Paulo Research Foundation) and CNPq (The National Council for Scientific and Technological Development). References Aguilar, A.Y., Van Diest, A., 1981. Rock phosphate mobilization induced by the alkaline uptake pattern of legumes utilizing symbiotically fixed nitrogen. Plant and Soil 61, 27–41. Andrade, F.V., Mendonc¸a, E.S., Alvarez, V.V.H., Novais, R.F., 2003. Adic¸a˜o de a´cidos orgaˆnicos e hu´micos em Latossolos e adsorc¸a˜o de fosfato. Revista Brasileira de Cieˆncia do Solo 27, 1003–1011. Bo¨hm, W., 1979. Methods of Studying Root System. Springer-Verlag, Berlin. Borkert, C.M., Gaudeˆncio, C.D.A., Pereira, J.E., Pereira, L.R., Oliveira Junior, A. de O., 2003. Nutrientes minerais na biomassa da parte ae´rea em culturas de cobertura de solo. Pesquisa Agropecua´ria Brasileira 38, 143–153.
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