Tillage management impacts on soil compaction, erosion and crop yield in Stagnosols (Croatia)

Catena 160 (2018) 376–384

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Tillage management impacts on soil compaction, erosion and crop yield in Stagnosols (Croatia)

MARK

Igor Bogunovica, Paulo Pereirab,⁎, Ivica Kisica, Krunoslav Sajkoa, Mario Srakac a b c

Department of General Agronomy, Faculty of Agriculture, University of Zagreb, Svetosimunska 25, 10000 Zagreb, Croatia Environmental Management Center, Mykolas Romeris University, Ateities g. 20, LT-08303 Vilnius, Lithuania Department of Soil Science, Faculty of Agriculture, University of Zagreb, Svetosimunska 25, 10000 Zagreb, Croatia

A R T I C L E I N F O

A B S T R A C T

Keywords: Land degradation Contour tillage Soil compaction Crop yields

The sustainability of agroecosystems is closely related to successful soil conservation. Sustainable land use practices are crucial to reduce the impacts of agriculture on land degradation and maintain long-term soil productivity. In this context, is important to avoid practices that deteriorate the soil (e.g. soil erosion), and find the most suitable to maintain soil and crops productivity. The objective of this work is to compare the impact of different tillage systems on soil compaction, erosion and crop production on clay loam Stagnosols in Croatia. Three tillage treatments were studied: conventional tillage (CT), no-tillage (NT) and deep tillage (DT). Soil water content, bulk density and penetration resistance were determined in the 0–10, 10–20, 20–30 and 30–40 cm soil depths. Soil erosion was measured during rainfall events. The results showed that tillage treatments influenced the soil physical parameters, soil loss and crop yields. During first four years of study NT increased (p < 0.05) bulk density in the 0–10 cm depth by an average of 8% and 7% in relation to CT and DT. Conventional tillage treatment increased (p < 0.05) bulk density in the 30–40 cm depth by an average of 6% and 5% in relation to NT and DT. No-tillage treatment had a significantly higher penetration resistance (PR) comparing to CT and DT in 2012 and 2014. During the flowering time of 2013, PR was significantly higher in NT at 20–30 cm depth than in the other treatments. This was observed also in 2014 at 20–30 and 30–40 cm depth. Average annual soil loss under NT (0.53 t ha− 1 year− 1) and DT (3.11 t ha− 1 year− 1) were significantly lower than that under CT (13.11 t ha− 1 year− 1). No-tillage had lower crop grain yields compared to CT and DT, but higher yields in dry years, as consequence of the high capacity for water retention. We recommended DT treatment for investigation at the field scale to assess its suitability for wider application on clay loam soils on sloped areas.

1. Introduction Soil tillage type can have both negative and positive effects on soil physical properties. Conventional tillage (CT) practices, that involve mouldboard ploughing decreases soil organic matter (Troldborg et al., 2013), and increase compaction, soil crusting, and erosion and damage soil biota (Kladivko, 2001; Birkás et al., 2008; Hösl and Strauss, 2016). Conventional tillage on sloped areas can lead to the high soil loss rates, especially if is performed in up-slope and down-slope directions (de Alba, 2003; Bertol et al., 2007; DeLaune and Sij, 2012). The majority of farmers (> 90%) in Croatia plough the soil annually, as a primary tillage procedure (Bogunovic et al., 2017). This practice results in high rates of erosion (e.g. Kisic et al., 2002, 2017). Therefore, there is a need for more sustainable soil management practices. On the other hand, notillage (NT) practices preserve soil quality and reduce soil erosion (Lal, 2007; Sasal et al., 2010; Mwango et al., 2016). This practice is not

⁎

common in Croatian Stagnosols, mostly because farmers are still wary about soil compaction, variable crop yields and incorporating lime under NT (Bogunovic and Kisic, 2017). Conventional tillage practices may affect soil physical properties, both positively and negatively (Alvarez and Steinbach, 2009), which results in highly variable crop yields. Several studies have recorded higher crop yields under CT compared to under NT (e.g., Van den Putte et al., 2010; Tolon-Becerra et al., 2011), whereas others found no differences (e.g., Shipitalo and Edwards, 1998; Dı́az-Zorita et al., 2002). Despite the relevance of the topic, very little research has been carried out on different tillage systems on soil degradation and their influence on crop production in Croatian Stagnosols (Basic et al., 2001, 2004). The effect of tillage treatments on grain production in clay loam soils under pre-humid to humid conditions, is not well understood or documented. The aim of this work is to study: i) the impacts of tillage treatment on soil water content (SWC), compaction, and erosion; and ii) to identify the optimal

Corresponding author. E-mail addresses: [email protected] (I. Bogunovic), [email protected] (P. Pereira), [email protected] (I. Kisic), [email protected] (K. Sajko), [email protected] (M. Sraka).

http://dx.doi.org/10.1016/j.catena.2017.10.009 Received 30 June 2017; Received in revised form 18 September 2017; Accepted 7 October 2017 0341-8162/ © 2017 Elsevier B.V. All rights reserved.

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2.2. Experimental design and management practices

Table 1 Soil profile characteristics of a Stagnosol. Values following ± indicate standard deviation. Horizons

Ap + Eg

Eg + Btg

Btg

Depth range (cm) pH in KCl (w/w 1:2.5) Organic matter (g kg− 1) Available P2O5 (g kg− 1) Available K2O (g kg− 1) Clay (< 0.002 mm) (g kg− 1) Silt (0.02–0.002 mm) (g kg− 1) Fine sand (0.2–0.02 mm) (g kg− 1) Coarse sand (2–0.2 mm) (g kg− 1) Texture classification

0–24 4.21 ± 0.15 16 ± 3.3 172 ± 18 308 ± 6 235.8 ± 9.0 291.2 ± 42.1 465.1 ± 47.9

24–35 4.20 ± 0.18 14 ± 4.2 65 ± 4 123 ± 8 241.3 ± 6.9 273.4 ± 7.2 479.8 ± 8.4

35–95 4.81 ± 0.23 6 ± 3.8 244 ± 24 502 ± 12 230.3 ± 11.7 289.0 ± 39.9 476.1 ± 40.5

7.9 ± 1.4

5.6 ± 1.0

4.6 ± 1.1

Clay loam

Clay loam

Clay loam

The experimental plots were established in the summer of 1994. Consisted of six treatments, each with 25 m wide and 50 m long in slopes that were approximately 9%. The tillage treatments differed in terms of the tools that were used, along with the depth and direction of tillage. For this study, the three tillage treatments were considered: Conventional tillage (CT), which involves mouldboard ploughing upand down slope with a 5-bottom Nardi reversible plough to a depth of 30 cm. The preparation of the seedbed was carried out up and down the slope with a combined Vaderstad tool; Deep tillage (DT) consisted of ploughing across the slope to a depth of 30 cm, with subsoiling to a depth of 50 cm. Annual tillage was similar to the CT system. The difference between CT and DT was the tillage direction and the occasional deep tillage that occurred in DT. Both treatments incorporated plant residues into the soil by ploughing. Every 3–4 years during the summer, when crop rotation allowed for it, deep loosening to a depth of 50 cm was performed with a V-frame 7 shank subsoiler under DT. No-tillage (NT) treatment induced no soil disturbance, and only involved seeding with a John Deere 750A NT planter in an up- and down slope direction. The weeds were controlled with total and pre-emergence herbicides. The plant residues of the investigated crops were retained on the soil surface. In this tillage treatment, no cultivation was carried out from the beginning of the research. The crops grown on each experimental plot followed a typical rotation that included maize, soybean, winter wheat, oilseed rape, and double-crop spring barley with soybean. Primary tillage for summer crops (maize, soybean) was implemented during October or November in the previous autumn, and supplementary tillage followed in the spring (April or March), prior to planting. Tillage practices for winter crops (primary and secondary) were carried out in September (oilseed rape) or October (winter wheat). The most important dates and information about tillage, sowing, fertilization and harvest are shown in Table 2.

tillage most appropriate for crop yields. The following hypotheses were tested: (i) NT treatments enable preservation of soil physical quality, preventing the formation of tillage-induced compaction; (ii) periodic subsoiling will provide a loose subsurface horizon and will provide higher crop yields; and (iii) NT treatments will prevent soil loss regardless of crop rotation. 2. Materials and methods 2.1. Study site The experiment was conducted in Pannonian Croatia at 45° 56′ N, 17° 02′ E at 129 m above sea level. The parent material in the study area is composed of loamy loess sediments that developed a Pseudogley soil (Škorić et al., 1985). Pseudogley soils properties are highly correlated with Stagnosols or Albeluvisols (IUSS Working Group WRB, 2006). The general properties of the studied soils are shown in Table 1. Pseudogley, is the second most frequent soil type in Croatia (Bogunović et al., 1998). > 55% of the area covered by this soil type is used for agriculture (Husnjak et al., 2011). In the Pannonian Croatia, Pseudogley subsoil is normally compacted between 25 and 55 cm depth (Rubinić et al., 2014, 2015). Despite this natural limitation for agriculture, these soils are intensively used for crop production (Bogunović et al., 1998). The climate is temperate continental, with an average rainfall of 889 mm (1961–1999). Rainfall distribution is not uniform throughout the year, particularly in the spring and autumn, when most of the highintensity rains occur. The mean annual temperature is 10.7 °C, ranging from − 0.4 °C in January to 20.6 °C in July (1961–1999).

2.3. Soil sampling, penetration resistance measurements and laboratory analysis Each spring and autumn, from 2007 through the fall of 2014, the bulk density and SWC was measured. Exceptions were made in 2010, when sampling was performed only in the autumn, and in 2011, when no sampling was performed. Penetration resistance measurements were carried out only in 2012, 2013 and 2014, at seeding and flowering time. Penetration resistance was determined with an electronic

Table 2 Summary of cultural practices for each growing season in the study area. Season

Crop

Fertilization

Tillage

Sowing date

Harvest date

Sep 8

Sep 8

Jun 19, 2007

Apr 30

May 1

Oct 1, 2008

Oct 10, 2008

Apr 03

Apr 04

Sep 22, 2009

Oct 14, 2009

Oct 14 Sep 10

Oct 15 (Apr 23) Sep 10

Jul 7 (Oct 3) 2010 Jun 29, 2011

Apr 29

Apr 30

October 1

Oct 26 Mar 17

Oct 26 Mar 18 (Apr 12)

Jul 18 Jul 19 (Spring barley)

Ploughing

2006/07

Oilseed rape

2007/08

Maize

2008/09

Soybean

2009/10 2010/11

Winter wheat + Soybean Oilseed rape

2011/12

Maize

2012/13 2013/14

Winter wheat Spring barley + soybean

NPK 7:20:30 (500 kg ha− 1); KAN 27% (270 kg ha− 1) Urea 46% (150 kg ha− 1); NPK 7:20:30 (400 kg ha− 1); KAN 27% (300 kg ha− 1) NPK 7:20:30 (300 kg ha− 1); KAN 27% (200 kg ha− 1) KAN 27% (250 kg ha− 1) NPK 7:20:30 (300 kg ha− 1); KAN 27% (250 kg ha− 1) Urea 46% (200 kg ha− 1); NPK 7:20:30 (400 kg ha− 1); KAN 27% (250 kg ha− 1) KAN 27% (550 kg ha− 1) KAN 27% (150 kg ha− 1)

Subsoiling

Sep 7, 2006 Apr 30, 2008

Sep 09, 2010

Aug 2, 2007

Jul 9, 2011

Nov 18, 2011 Oct 25, 2012 Oc 28, 2013

Note: KAN - Calcium ammonium nitrate (N 27%, Ca + Mg 13%).

377

Oct 27, 2013

Seedbed preparation

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2.5. Statistical analysis

hand-pushed cone penetrometer (Eijkelkamp Penetrologger) using a cone with 2 cm2 base area, with a 60° included angle and 80 cm driving shaft. In total, we measured 16 sampling points per treatment at 0–10 cm, 10–20 cm, 20–30 cm and 30–40 cm. Sample cores were collected from non-traffic areas on each plot, and no attempt was made to keep track of the subsoiler. Sampling was carried out by sampling cores of 100 cm3 volume at the same soil depths that we measured PR. We sampled 3 replicates per site. Furthermore, during 2012 and 2013, soil cores were sampled from 0 to 10, 10–20 and 20–40 cm. Overall, 36 soil cores were collected per measurement (30 cores for each measurement during 2012 and 2013). Four hundred and forty four undisturbed samples were collected. The bulk density and SWC were determined on an oven-dry mass basis (the samples were dried in an oven at 105 °C for 48 h). The SWC data are presented in mm by multiplying the water content by the soil depth and corresponding bulk density. Each year during the harvest, three passes of the harvester were done to determine the crop grain yields. Afterwards, seeds were cleaned and weighed and the obtained values were corrected to a 14% SWC.

Prior to applying statistical procedures, the data were checked for normality with the Kolmogorov – Smirnoff test and homogeneity of the variances with Levene's test. Bulk density and SWC followed normal distribution. Significant differences between bulk density and SWC were assessed with an ANOVA test. Penetration resistance, annual soil loss and crop yields data did not follow a normal distribution. Thus, the data square-root and logarithmic transformations were carried out to achieve normality before carrying out the ANOVA test. In cases where ANOVA showed significant differences at p < 0.05, a Tukey's post hoc test was applied. Statistical analyses were computed with the SAS 9.3 software package (SAS Institute Inc., NC, USA). 3. Results 3.1. Rainfall pattern and soil water content The different rainfall events recorded in the plots during the nine seasons are shown in Table 3. The driest crop year was 2011 and the wettest was 2014. The weather conditions in the remaining years were within the average values, except for 2009, which was the second driest year during the studied period. Several dry periods occurred. The results of tillage influence on the SWC are displayed in Fig. 2. Significant differences were identified only in 2013, considered a dry year. NT and DT had a significantly higher SWC than CT (Fig. 2).

2.4. Erosion plots and sediment collector's characteristics Within each tillage treatment, a sheet-metal border was placed into the soil to monitoring erosion. The isolated plot area had 41.3 m2 (22.1 m long and 1.87 m wide). The sheet-metal borders were removed before tillage and then replaced for monitoring soil erosion during the growing season. Metal borders were inserted 20 cm deep in the soil and 10 cm remained above. Sediment and water collectors were established in each treatment to measure soil erosion and surface runoff (Fig. 1). Clean water was collected in a separate container, whereas sediment remained on the filter cloth. The suspension came from the enclosed erosion plot (41.3 m2) to the first tank that retained plant residues. The second tank contained a permeable fabric that retained soil, whereas the clean water flowed into the last tank. The sediments collected were taken to the laboratory for air drying and weighing to measure the sediment yield. After each erosion event, the runoff and sediment yield were collected. In total, from 2007 to 2014, 94 sediment samples were sampled after 57 erosion events.

3.2. Bulk density and penetration resistance Bulk density was significantly influenced by tillage in 2007, 2010 and 2014 and depth during all studied period. An interaction between tillage × depth was identified during all the study, with the exception of 2009 and 2013 (Table 4). The Fig. 3A-E shows the soil bulk density according to the depth. No-tillage treatment had a significantly higher bulk density in the 0–10 cm depth in 2007, 2008 and 2010, compared to the tilled treatments. In the 10–20 cm depth, no significant differences were found during the entire study period. At 20–30 depth NT and DT treatments, bulk density was normally higher than CT, with the

Fig. 1. Experimental plot.

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Table 3 Monthly and annual rainfall (mm) from 2006 to 2014. Months

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Total

%

1961–1999 2006 2007 2008 2009 2010 2011 2012 2013 2014 2006–2014 CV%

55 32.9 49.9 43.7 70.5 93.9 12.1 25.7 88.5 42.6 51.1 54.6

47 28.3 62.3 9.4 33.2 65.9 13.5 34.4 156.5 84.3 54.2 84.4

58 54.5 87.1 90.7 45.1 68 21 8.9 48.5 27.7 50.2 56.5

73 78.2 7 60.8 10.8 74.4 16.5 50.9 82 105.4 54.0 65.4

88 111.2 123.4 37.1 33.9 164.4 20.3 118.4 73.2 224 100.7 66.6

97 89.7 29 145.6 101.8 181.7 49.5 85.1 30.4 48.3 84.6 62.1

85 11.2 14.3 106.6 40.5 55.3 89.9 31.9 59.1 147.2 61.8 73.1

82 145.2 82.4 40.7 49.9 75.4 51.5 2.8 35.1 139.1 69.1 68.5

88 61.3 131.2 69.6 8.7 198.8 18.2 69.6 80.1 197.9 92.8 74.9

70 26 102.2 53.1 61.9 41 50.5 96.9 22.5 129.5 64.8 56.7

83 35.3 73.5 51.4 89.8 95.2 0 70.4 100.7 30.2 60.7 56.0

63 36 66.9 97.5 85.1 61.6 78.2 125.5 0.9 65.7 68.6 51.9

889 710 829 806 631 1176 421 721 778 1242 812.7 31.5

100 80 93 91 71 132 47 81 88 140 91

exception of 2007, where NT was lower than the other managements. This situation was inverted at 30–40 cm depth, CT had a higher bulk density than DT and NT, with the exception of 2007. Penetration resistance were significantly affected by treatment and depth during seeding time in 2012 and 2014. In 2013, significant differences were only observed in depth. In the flowering time, significant differences between tillage and depth were identified only in 2014. In 2012 and 2013, significant differences were only founded in depth. Interaction between tillage × depth was identified for seeding time in 2012 and 2014, while for flowering time, was observed in 2013 and 2014 (Table 5). Significant differences were observed in the seeding time of 2012 and 2014 in all depths. No-tillage treatment had a significantly higher PR than CT and DT at 0–10 and 10–20 cm. At 20–30 and 30–40 cm, NT and CT bulk density were higher than DT. During the flowering time, PR showed significant differences in 2013 (20–30 cm) and 2014 (20–30 cm and 30–40 cm). Penetration resistance was significantly higher in CT than in NT and DT (Fig. 4). This results confirmed the observed in bulk density analysis. Conventional tillage management increases soil compaction in the deepest soil layers.

Table 4 Bulk density ANOVA results.

Tillage (T) Depth (D) T×D

d.f.

2007

2008

2009

2010a

2012

2013

2014

2 3 6

* *** ***

n.s. *** **

n.s. *** n.s.

* *** ***

n.s. *** *

n.s. *** n.s.

*** *** *

*P < 0.05; **P < 0.01; ***P < 0.001; ns (not significant at a p < 0.05). a Measurements were conducted only in fall.

NT treatment compared to CT and DT treatments in 2009, as well as wheat and barley grain yields in 2013 and 2014. On average, DT and CT showed substantially higher yields compared with NT, but the differences varied with growing season. Oilseed rape did not significantly respond to tillage in the 2006/2007 and 2010/2011 seasons, whereas winter wheat recorded the highest grain yields in both seasons under the CT treatment. Deep tillage resulted in the highest yields in 2008 and 2009, whereas NT recorded the highest yield of maize in 2012. 4. Discussion

3.3. Soil loss

4.1. Rainfall pattern and soil water content

Annual soil loss and the number of erosion events are presented in Table 6. Average annual soil erosion (the mean from all seasons) was significantly higher in CT than in the other treatments. For CT ad DT treatment, the highest average annual soil erosion were 46.20 t ha− 1 and for maize (2012), for NT 7.57 t ha− 1, respectively. For NT, the highest annual average soil erosion was observed in soybean (1.22 t ha− 1) in 2009.

The study results confirm the idea that differences between the NT and CT were higher in dry years. The high SWC in NT during dry years may be attributed to the reduced evaporation rates and high infiltration. Residues in NT treatments generally increase the albedo, reduce the heat flux into soil, and increase the aerodynamic resistance to reduce vapour flux and consequently, water losses (Lascano and Baumhardt, 1996). Our results are in agreement with Alvarez and Steinbach (2009), who found greater advantage of NT for SWC in the semiarid regions (dry conditions) compared to humid regions (wet conditions) of Pampas. The significantly high SWC in DT than in CT in 2013, is due to the fact that subsoiling increases the hydraulic conductivity comparing to ploughing (Hamza and Anderson, 2005; Birkás et al., 2008; Alvarez and Steinbach, 2009). Butorac et al. (1981)

3.4. Crop yields The yield data for all crops are shown in Fig. 5. Tillage treatments had a significant effect on grain yields in 2008, 2009, 2013 and 2014. In 2008, NT had significantly lower yields compared to DT, but it did not differ from CT. Soybean grain yields were significantly lower under the

Fig. 2. Tillage effect under conventional tillage (CT), no-tillage (NT) and deep tillage (DT) on the soil water content at 0–40 cm depth between 2007 and 2014. Significant differences were observed at p < 0.05*. ns (not significant at a p < 0.05). The soil water content in mm. Hanging bars represent the standard deviation.

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Fig. 3. Soil bulk density under conventional tillage (CT), no-tillage (NT) and deep tillage (DT) at 10, 20, 30 and 40 cm depth. Different letters for each depth indicate significant differences at p < 0.05 among the treatments. ns (not significant at p < 0.05).

reduction of aggregate stability and organic matter loss (Elliott, 1986; Six et al., 2000; Troldborg et al., 2013). Earlier studies confirmed that Stagnosols have a poor structure and low aggregate stability (Basic et al., 2004; Rubinić et al., 2014), which increases the vulnerability to settling and compaction. Coupled with these factors, during the studied seasons an important amount rainfall occurred during the winter (Table 3). The kinetic energy of rain resulted in soil settling (e.g., Nanko et al., 2015), mostly at surface. Alletto and Coquet (2009) found that a few weeks after tillage, the benefits were lost in silty soil as a result of gravity and rainfall, whereas Osunbitan et al. (2005) recorded a 55–61% increase in bulk density in tilled treatments 8 weeks after soil tillage (0–15 cm). Re-compaction of subsurface depths is also pronounced. According to Busscher et al. (2002) 67–91% of re-compaction after tillage could be attributed to rainfall, and they found that water filtering through the soil may cause settling. Re-compaction is temporally greater in surface soils compared to subsurface soils, which is also confirmed by Alletto and Coquet (2009). The second reason for the absence of differences between the NT and tillage treatments at 0–10 cm depth is long-term application of the NT treatment. During a transition from tilled soils to NT, problems occur during the first years because of the physical properties of the previously deteriorated soils. The absence of tillage and the cumulative effect of historical agricultural machinery traffic increases topsoil density (de Moraes et al., 2016). Ten or more years after NT treatment, soil physical properties start to improve (Alvarez and Steinbach, 2009). Soils under NT treatment was not disrupted by tillage, and biopores created from root growth and faunal activities remained undisturbed (Gantzer and Blake,

observed the similar results in this study area during the autumn and winter season. In other environments, Grant and Lafond (1993) and Alvarez and Steinbach (2009) identified that NT treatments retained more water than CT. 4.2. Bulk density and penetration resistance The results obtained indicate that the NT treatment had implications for the top soil bulk density in the beginning of the experiment. Bulk density was higher under the NT treatment than under the CT and DT at 0–10 cm depth in 2007, 2008 and 2010. This is agreement with other studies. (e.g., Grant and Lafond, 1993; Singh et al., 2014a; Gao et al., 2016). Gao et al. (2016) found that the soil bulk density was greater after 3 years of NT compared with tilled treatments on a clay loam soil. Similar results were reported on sandy clay soils in Chile (Martínez et al., 2008) and on clay loam soils in India (Singh et al., 2014a). The results for the 0–10 cm depth from 2011 to 2014, as well as for the 10–20 cm depth over the whole study period, indicate that the NT treatment did not statistically differ from the tilled treatments. This could be explained by two factors. First, mouldboard ploughing was applied every year (in the CT and DT treatments) in the autumn, and several months passed prior to the first spring measurement, thereby allowing time for soil consolidation and bulk density increase. Tillage impact on Stagnosols is not persistent. Usually, tilled soils lose their structure and resistance to compaction due to intensive management (Nawas et al., 2013). Tillage induces deterioration of soil structure, Table 5 Penetration resistance ANOVA results. d.f.

Tillage (T) Depth (D) T×D

2 3 6

2012

2013

2014

Seeding

Flowering

Seeding

Flowering

Seeding

Flowering

*** *** ***

n.s. *** n.s.

n.s. *** n.s.

n.s. *** *

*** *** ***

*** *** ***

*P < 0.05; **P < 0.01; *** P < 0.001; ns (not significant at a p < 0.05).

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Fig. 4. Vertical distribution of penetration resistance (MPa) for three growing seasons under (CT) conventional tillage, (NT) no-tillage and (DT) deep tillage. Values with different letters (horizontally) are significantly different at each depth (p < 0.05) among the treatments. ns (not significant at a p < 0.05).

1978). These findings indicate that under NT, biopores minimise the impact of differences in bulk density among treatments. Furthermore, redistribution and accumulation of organic matter in the soil surface may have occurred, as noted in previous studies (e.g., Six et al., 2000; Singh et al., 2016). These processes are probably a result of the established equilibrium balance that causes the decrease of bulk density in topsoil. Soil compaction at a depth of 30–40 cm was higher in CT than in NT, whereas DT showed lower bulk density compared to CT. However, DT did not statistically differ from NT. These findings can be explained by the formation of tillage-induced hardpan (“plough pan”) under the CT treatment. This is a result of long-term ploughing to the same depth, as we observed in our work. To our knowledge, annual ploughing was used as the tillage method for at least 30 years before this experiment was established. Our results are similar to those of Singh et al. (2014b), who noticed lower macroporosity and de Moraes et al. (2016), who

found higher bulk density on the edge of tillage, indicating the formation of hardpan. A similar bulk density between NT and DT in the 30–40 cm depth could also be the result of a higher formation of biopores, as noted by Soracco et al. (2012), or due to short-lived subsoiling. Conventional Tillage and DT PR was lower than NT and this was attributed to soil tillage. Tilled managements had higher changes in PR comparing to NT. Mouldboard ploughing followed by a secondary tillage decreased the relative compaction in the seeding period, although the PR reduction varied each year. These results are consistent with the findings of Tolon-Becerra et al. (2011), which observed that in a three year study, NT had a significantly higher PR in all investigated depths compared to chisel and mouldboard tilled treatments. Similar results were also observed in previous works (e.g., Singh et al., 2016; Gao et al., 2016). Penetration resistance changes importantly in soils subjected to

Table 6 Annual values of soil loss (ASL), the lowest soil loss (Min) and the highest soil loss (Max) (t ha− 1 year− 1) with a corresponding number of erosion events (n), for three tillage treatments: conventional tillage (CT), no-tillage (NT) and deep tillage (DT) treatments. Season

Crop

Treatment CT

Oilseed rape Maize Soybean Double Oilseed rape Maize Winter wheat Double Mean Sum a

06/2007 2008 2009 09/2010 10/2011 2012 12/2013 13/2014 2007–14 2007–14

NT

DT

n

ASL

Min

Max

n

ASL

Min

Max

n

ASL

Min

Max

8 4 5 6 4 8 6 16 7 57

5.56 15.92 13.82 1.55 2.06 46.20 5.16 14.57 13.11aa 104.84

0.03 0.25 0.15 0.03 0.02 0.42 0.14 0.01

2.90 8.21 3.81 0.85 1.78 19.2 3.08 7.2

1 1 1 4 – 2 2 3 2 14

0.29 0.85 1.22 0.56 – 0.31 0.32 0.16 0.53b 3.71

0.29 0.85 1.22 0.50 – 0.14 0.07 0.07

0.29 0.85 1.22 0.02 – 0.17 0.25 0.14

2 2 4 2 1 2 3 7 3 23

1.44 3.56 5.76 0.42 0.001 7.57 3.23 2.92 3.11b 24.90

0.51 1.66 0.09 0.09 0.001 2.81 0.51 0.003

0.93 1.90 4.49 0.34 0.001 4.76 2.08 2.12

Values with different letters are significantly different (p < 0.05) among the treatments.

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Fig. 5. Conventional tillage (CT), no-tillage (NT) and deep tillage (DT) effects on grain yield between 2007 and 2014. Values with different letters are significantly different (p < 0.05) among the treatments. Grain yield is in t ha− 1. Hanging bars represent the standard deviation.

known that contour tillage results in lower soil loss compared to upslope and down-slope tillage, regardless of the soil type and climate conditions (e.g., Chisci and Boschi, 1988; Quinton and Catt, 2004; Stevens et al., 2009). The results indicate that a change in tillage direction (DT) can minimise soil loss by 73% on average compared to tillage up and down the slope (CT). This is in agreement with Quinton and Catt (2004), who noticed that contour tillage reduces soil loss by 76% compared with tillage performed in an up-slope and down-slope direction. On the other hand, the study results showed a reduced soil erosion under NT treatment. Regardless of cover crop, the annual soil loss was not higher than 1.22 t ha− 1. Long-term NT treatment with residue retention improves soil properties. Twenty-four years after NT management, significantly decreased runoff and soil erosion compared with CT and DT (Zhang et al., 2007; Vaezi et al., 2016). This long-term approach to soil management resulted in a high accumulation of plant residues on the surface, which reduces the effect of splash erosion (Nanko et al., 2015). Cerda et al. (2016) found that on loamy soils, surface residues significantly reduce soil erosion rates even after high magnitude rainfall events. Hösl and Strauss (2016) recorded lower total soil loss under NT on silt loam soil compared to conventionally tilled soils. Lal (1997) found an important decrease in soil erosion under NT compared to under CT, regardless of the slope length. However, for the purposes of wider comparison, it is necessary to know the timing of transition to a NT system. For instance, in the first two years after the transition to a NT system Basic et al. (2004) recorded extremely high soil loss under NT, attributed to the lack of residue cover maintenance after the transition to NT (Wilson et al., 2008). Overall, NT treatments have been proven to result in advantages in preserving soil from erosion in arid (Cerda et al., 2016), humid (Shipitalo and Edwards, 1998) and tropical (Lal, 1997) climate conditions, and the results of the present study indicate its effectiveness in semi-humid temperate conditions. Crops, as residue cover, protect the soil from raindrop impacts and are a key factor in controlling erosion. The results of this study suggest that the high soil loss were attributed to bare soil after seedbed preparation. This exposed the topsoil to raindrop impacts, and therefore to compaction and erosion. This especially relevant during intense rainfall periods such as May–June (Table 3), increasing the erosion rates in the studied plots. After the crops were growing, the occurrence of higher crop biomass under CT in maize and soybean did not reduce soil loss compared to under NT as consequence of the high proportion of unprotected soil between the rows. Severe surface runoff and erosion have been reported when ground cover decreases below 50% (Ochoa-Cueva et al., 2015; Nanko et al., 2015). The reason for lower erosion under NT is the presence of mulch cover, which protects the soil in the period before the crops are sown. High reductions in soil loss under mulching have been reported globally (e.g., Nishigaki et al., 2016; Prosdocimi et al., 2016; Mwango et al., 2016). Therefore, high erosion was noted under the CT maize and soybean (Table 5) but not under DT treatments, even though the tool used for soil preparation was the same. These results for DT are in agreement with other studies (Chisci and Boschi, 1988; Shipitalo and Edwards, 1998) and can be justified by the

different managements (Whitmore et al., 2011). Soil consolidation and drying is responsible for the temporal variation in PR and bulk density. Previous studies found that the differences in PR between NT and tilled treatments were high immediately after tillage, decreasing rapidly to similar levels at the end of the season (Franzen et al., 1994; Lopez et al., 1996; Yavuzcan et al., 2005). This is an evidence that CT and DT soils are vulnerable to re-compaction. Two MPa is the threshold for normal root development (Taylor and Gardner, 1963), whereas at 2.5 MPa, the roots stop penetrating the soil (Taylor, 1971). Håkansson and Lipiec (2000) and Birkás et al. (2008) argued that the limit should be between 2.8 and 3.2 MPa. For comparison proposes we defined 3.0 MPa for root development restriction. In 2012 and 2013 during the flowering stage, PR was > 3.0 MPa at depths of 20–40 cm, limiting root development. In 2014 this was not observed, and was attributed to the wet conditions during the growing season (Table 3). This shows that independently of the treatment, during the flowering season the soil deeper layers restrict root development. This situation is reduced in wet years such as 2014. Penetration resistance increased with depth, in all the studied years and treatments. The highest values were always at 30–40 cm depth. This is a consequence of the overburden pressure and internal soil friction (Whitmore et al., 2011; Gao et al., 2016). Generally, in all treatments, bulk density was high at deeper layers (Fig. 3). Furthermore, a significantly lower PR under the DT treatment was recorded at 30–40 cm, in 2012 seeding time, and seeding and flowering stage in 2014. This was attributed to the subsoiling performed in the summers of 2011 and 2013. Our results are support the idea that in heavy soils, persistence of subsoiling/ripping lasts only 1 to-2 seasons (Bishop and Grimes, 1978; Dı́az-Zorita et al., 2002; Chan et al., 2006), although persistence of subsoiling depends on the soil type, annual rainfall and control of trafficking. In contrast, we observed that the highest values of PR were registered in CT treatment at 30–40 cm depth, and this indicates the presence of a plough pan, as observed in bulk density results. Conventional tillage management led to the occurrence of a CTinduced pan. According to Birkás et al. (2004), three years of soil ploughing using a mouldboard or disc plough induce a compaction on the depth border of the tilled layer. If this treatment is applied during 5 years, the compacted layer increases in depth. In this context, CT treatment is inducing very negative impacts on soil depth layers. This has a special importance in the land use of the studied area, since is the most used type of soil management.

4.3. Soil loss Our results provide an important evidence that the erosion in CT treatment is substantially higher than in the other management types. Therefore, it is not the best tillage practice regarding soil conservation. In addition, erosion decreases with decreasing tillage intensity and changing tillage direction. This was especially observed in spring crops. This study confirm the hypothesis that tillage and the direction of tillage has a strong influence on soil loss on sloped terrain. It is a well-

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autumn period. Our study results supported this statement for 2008 and 2012. Several months after subsoiling in 2007 and 2011 (Table 2), the DT treatment recorded higher yields of maize compared to the CT (Fig. 5). Subsoiling loosened the subsoil, retained more water and induced greater root spreading compared to CT. Nevertheless, benefits of subsoiling rapidly diminished after one season (Fig. 3), and in combination with crops with lower demand for deeper rooting, DT did not show any advantage in crop yield compared to the CT treatment. As mentioned previously, the benefits of soil loosening on soil physical properties last for one or two seasons (Dı́az-Zorita et al., 2002; Chan et al., 2006; de Moraes et al., 2016), and mostly depended on soil stability, trafficking and rainfall.

existence of surface roughness, which is in this case, 5–8 cm of height in an across-slope direction, but their existence is still effective to prevent soil loss, as proven by Vieira and Dabney (2011). The presence of bare soil after sowing high-density winter crops did not increase erosion rates. A possible explanation is the existence of stable aggregates created by primary tillage, which was usually performed a few days before sowing winter crops (Table 2). Furthermore, oilseed rape, winter barley and winter wheat are sown at the end of summer or in autumn, when the occurrence of strong thunderstorms is lower comparing to spring. Accordingly, germination and emergence of these crops starts within 10–15 days, and their canopies develop relatively fast compared to maize and soybean. Winter crops create a thick cover on the ground in a relatively short period, and reduce potential soil losses. Even though, the data in Table 3 indicate that the magnitude of rainfall was high in autumn and spring, individual soil losses under high-density winter crops were variable and not always explained by monthly rainfall (data not shown). Instead, individual event losses probably depended on the complex interaction between earlier soil structure, SWC, rainfall intensity patterns and the development of the crop canopy. After a period of low intensity winter rains, the canopy cover of high-density winter crops and the frozen soil, may have been the cause for the reduced soil erosion. Lower rates of soil loss under high-density crops compared to wide row crops have been reported in several works (Shipitalo and Edwards, 1998; Basic et al., 2004; Quinton and Catt, 2004; Shipitalo et al., 2013), which confirm the results presented here.

5. Conclusions Long-term NT favoured topsoil and subsoil bulk density and PR. Conventional tillage created of a subsoil hardpan. The outcomes of this study supported the hypothesis that subsoiling provides higher yields of crops compared to CT. Periodic soil loosening of Stagnosols should be implemented every 1–2 season, since the residual effects of loosening on the soil physical conditions are short-lived. An efficient reduction of soil erosion can be achieved by NT and DT contour tillage. To achieve stable yields, the DT treatment is recommended for wider application to similar soils and climatic conditions in order to mitigate soil erosion, reduce subsoil compaction and provide a stable grain yield. References

4.4. Crop yields de Alba, S., 2003. Simulating long-term soil redistribution generated by different patterns of mouldboard ploughing in landscapes of complex topography. Soil Tillage Res. 71, 71–86. http://dx.doi.org/10.1016/S0167-1987(03)00042-4. Alletto, L., Coquet, Y., 2009. Temporal and spatial variability of soil bulk density and near-saturated hydraulic conductivity under two contrasted tillage management systems. Geoderma 152, 85–94. http://dx.doi.org/10.1016/j.geoderma.2009.05.023. Alvarez, R., Steinbach, H.S., 2009. A review of the effects of tillage systems on some soil physical properties, water content, nitrate availability and crops yield in the Argentine Pampas. Soil Tillage Res. 104, 1–15. http://dx.doi.org/10.1016/j.still. 2009.02.005. Basic, F., Kisic, I., Butorac, A., Nestroy, O., Mesic, M., 2001. Runoff and soil loss under different tillage methods on Stagnic Luvisols in central Croatia. Soil Tillage Res. 62, 145–151. http://dx.doi.org/10.1016/S0167-1987(01)00214-8. Basic, F., Kisic, I., Mesic, M., Nestroy, O., Butorac, A., 2004. Tillage and crop management effects on soil erosion in central Croatia. Soil Tillage Res. 78, 197–206. http://dx.doi. org/10.1016/j.still.2004.02.007. Bertol, I., Englel, F.L., Mafra, A.L., Bertol, O.J., Ritter, S.R., 2007. Phosphorus, potassium and organic carbon concentrations in runoff water and sediments under different tillage systems during soybean growth. Soil Tillage Res. 94, 142–150. http://dx.doi. org/10.1016/j.still.2006.07.008. Birkás, M., Jolánkai, M., Gyuricza, C., Percze, A., 2004. Tillage effects on compaction, earthworms and other soil quality indicators in Hungary. Soil Tillage Res. 78, 185–196. http://dx.doi.org/10.1016/j.still.2004.02.006. Birkás, M., Szemők, A., Antos, G., Neményi, M., 2008. Environmentally-Sound Adaptable Tillage. Akadémiai Kiadó, Hungary. Bishop, J.C., Grimes, D.W., 1978. Precision tillage effects on potato root and tuber production. Am. Potato J. 55, 65–71. Bogunovic, I., Kisic, I., 2017. Soil compaction on clay loam soil in Pannonian region under different tillage system. J. Agric. Sci. Technol. 19, 475–486. Bogunović, M., Vidaček, Ž., Husnjak, S., Sraka, M., 1998. Inventory of soils in Croatia. Agric. Conspec. Sci. 63, 105–112. Bogunovic, I., Trevisani, S., Seput, M., Juzbasic, D., Durdevic, B., 2017. Short-range and regional spatial variability of soil chemical properties in an agro-ecosystem in eastern Croatia. Catena 154, 50–62. http://dx.doi.org/10.1016/j.catena.2017.02.018. Botta, G.F., Tolon-Becerra, A., Lastra-Bravo, X., Tourn, M., 2010. Tillage and traffic effects (planters and tractors) on soil compaction and soybean (Glycine max L.) yields in Argentinean pampas. Soil Tillage Res. 110, 167–174. http://dx.doi.org/10.1016/j. still.2010.07.001. Buschiazzo, D.E., Panigatti, J.L., Unger, P.W., 1998. Tillage effects on soil properties and crop production in the subhumid and semiarid Argentinean Pampas. Soil Tillage Res. 49, 105–116. http://dx.doi.org/10.1016/S0167-1987(98)00160-3. Busscher, W.J., Bauer, P.J., Frederick, J.R., 2002. Recompaction of a coastal loamy sand after deep tillage as a function of subsequent cumulative rainfall. Soil Tillage Res. 68, 49–57. http://dx.doi.org/10.1016/S0167-1987(02)00083-1. Butorac, A., Lacković, L., Beštak, T., Vasilj, Đ., Seiwerth, V., 1981. Efficiency of reduced and conventional soill tillage in interaction with mineral fertilizing in crop rotation winter wheat – sugar beet – maize on lessive Pseudogley. Agric. Conspec. Sci. 54, 5–30. Cerda, A., González-Pelayo, O., Jordan, A., Pereira, P., Novara, A., Brevik, E.C.,

The results obtained suggest that crop yields were more affected by other factors than by tillage. Crop yield depends on the interaction between rotation, management practices, soil properties and climate (Alvarez and Steinbach, 2009). The previous studies about CT and NT management are contradictory. Some researchers reported that crop yields increase under NT compared to CT (Lal, 1997; Singh et al., 2016) and the inverse as well (Botta et al., 2010; Tolon-Becerra et al., 2011). In other works, no differences in crop yields between CT and NT systems were observed (Shipitalo and Edwards, 1998; Alvarez and Steinbach, 2009). In semi-arid regions, crop yields are usually higher under NT because of the high water retention, compared to CT (Buschiazzo et al., 1998), whereas in wet conditions, CT treatments can produce higher crop yields (Alvarez and Steinbach, 2009). Grain yields of cereals in Pannonian Croatia are limited during water deficits in the flowering and fertility stage. Climate conditions in the studied area are semi-humid to humid, and a reduce SWC was identified in the summer period. The advantage of NT is that reduces the evaporation rates and increases water retention capacity in the dry years. This was what occurred in 2012, when the precipitation was reduced during the summer months. Despite NT did not differ significantly from other tillage treatments. In general, NT recorded the highest yield of maize. It is necessary to emphasise the inadequate weed management in NT during the early stages of all seasons. This created a high weed infestation, especially evident during the wet years. Is very likely that this type of management affected crop yields in the NT. Subsoiling in the DT treatment influenced the soil physical conditions in the first season (Fig. 3). In this season, grain yields were higher than CT (Fig. 5). Similar findings were reported by Franchini et al. (2012), which observed a reduction of soybean, maize and wheat yields in most of the growing seasons after the implementation of periodic loosening. Although, DT resulted in lower compaction in the subsoil horizon, compared to CT, the shoot growth and grain yields did not have a positive response. This depends on crops and their rooting depth. Winter crops usually root between 0 and 30 cm depth, and in humid years, there are no benefits from subsoiling. On the other hand, a positive response from subsoiling under DT could be observed for crops that have deeper rooting such as maize and soybean during summer and 383

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