Deep tillage and traffic effects on subsoil compaction and sunflower (Helianthus annus L.) yields

The main function of deep tillage is to alleviate subsoil compaction, but how long do the benefits of this technique remain? Traffic on loose soil causes a significant increase in soil compaction. Subsoiling and chisel plowing were carried out at 450 and 280 mm depth, respectively on a compacted soil in the west Rolling Pampas region of Argentina. The draft required, physical soil properties, root growth, sunflower (Helianthus annus L. Merr.) yield and traffic compaction over the subsequent two growing seasons were measured. Cone penetrometer resistance was reduced and sunflower yields increased following deep tillage operations. Subsoil compaction caused changes to the root system of sunflower that affected shoot growth and crop yields. Although subsoiling and chiseling had an immediate loosening effect, it was evident that after just 2 years, when traffic intensity was >95 mg km ha⁻¹, re-compaction and settling had occurred in the 300–600 mm depth range.     

Subsoil loosening in a crop rotation for organic farming eliminated plough pan with mixed effects on crop yield

Compacted subsoil may reduce plant root growth with resulting effects on plant uptake of water and nutrients. In organic farming systems subsoil loosening may therefore be considered an option to increase nutrient use. We investigated the effect of subsoil loosening with a paraplow to ca. 35 cm depth within a four-crop rotation in an organic farming experiment at Foulum (loamy sand) and Flakkebjerg (sandy loam) in Denmark. In each of the years 2000–2003, half of four plots per site were loosened in the autumn bearing a young grass-clover crop (mixture of Lolium perenne L., Trifolium repens L. and Trifolium pratense L.) established by undersowing in spring barley (Hordeum vulgare L.). The grass-clover was grown for another year as a green manure crop and was followed by winter wheat (Triticum aestivum L.), lupin (Lupinus angustifolius L.):barley and spring barley in the following 3 years. On-land ploughing was used for all cereal and pulse crops. Penetration resistance was recorded in all crops, and the results clearly showed that subsoil loosening had effectively reduced the plough pan and that the effect lasted at least for 3.5 years. Measurements of wheat root growth using minirhizotrons at Foulum in 2002/2003 did not show marked effects of subsoil loosening on root frequency in the subsoil. Subsoil loosening resulted in reduced growth and less N uptake of the grass-clover crop in which the subsoil loosening was carried out, probably due to a reduced biological nitrogen (N) fixation resulting from a smaller clover proportion. This had a marked effect on the growth of the succeeding winter wheat. Negative effect of subsoil loosening on yield of winter wheat and spring barley was observed without manure application, whereas small positive yield effect of subsoil loosening was observed in crops with a higher N supply from manure. Yield decrease in winter wheat was observed in years with high winter rainfall. There was no significant effect of subsoiling on grain yield of the lupin:barley crops, although subsoiling had a tendency to increase crop growth and yield during dry summers. Our results suggest that subsoil loosening should not be recommended in general under Danish conditions as a measure to ameliorate subsoil compaction.     

Subsoil compaction effects on crops in Punjab, Pakistan:II. Root growth and nutrient uptake of wheat and sorghum

Crop yields can be reduced by soil compaction due to increased resistance to root growth, and decrease in water and nutrient use efficiencies. A field experiment was conducted during 1997–1998 and 1998–1999 on a sandy clay loam (fine-loamy, mixed, hyperthermic Typic Haplargids, USDA; Luvic Yermosol, FAO) to study subsoil compaction effects on root growth, nutrient uptake and chemical composition of wheat (Triticum aestivum L.) and sorghum (Sorghum bicolor L. Moench). Soil compaction was artificially created once at the start of the study. The 0.00–0.15 m soil was manually removed with a spade. The exposed layer was compacted with a mechanical compactor from 1.65 Mg m⁻³ (control plot) to a bulk density of 1.93 Mg m⁻³ (compacted plot). The topsoil was then again replaced above the compacted subsoil and levelled. Both compacted and control plots were hoed manually and levelled. Root length density, measured at flowering stage, decreased markedly with compaction during 1997–1998 but there was little effect during 1998–1999. The reduction in nutrient uptake by wheat due to compaction of the subsoil was 12–35% for N, 17–27% for P and up to 24% for K. The reduction in nutrient uptake in sorghum due to subsoil compaction was 23% for N, 16% for P, and 12% for K. Subsoil compaction increased N content in wheat grains in 1997–1998, but there was no effect on P and K contents of grains and N and P content of wheat straw or sorghum stover. During 1997–1998, K content of wheat straw was statistically higher in control treatment compared with compacted treatment. In 1998, P-content of sorghum leaves was higher in compacted treatment than uncompacted control. Root length density of wheat below 0.15 m depth was significantly reduced and was significantly and negatively correlated with soil bulk density. Therefore, appropriate measures such as periodic chiselling, controlled traffic, conservation tillage, and incorporating of crops with deep tap root system in rotation cycle is necessary to minimize the risks of subsoil compaction.     

Crop and soil response to subsoil loosening, deep incorporation of phosphorus and potassium fertilizer and subsequent soil management on a range of soil types.: Part 1: Response of arable crops

Abstract. Between 1978 and 1985 16 experiments tested crop response to subsoil loosening by either the Wye Double Digger or a winged subsoiler. Additionally, response to incorporation of 350 kg ha of P₂O₅and K₂O into the subsoil was tested. Soil types were mainly well-drained light-and medium-textured soils in arable rotations. Subsoil loosening increased the yield of spring-sown crops on sandy soils in years of moderate to severe drought. Response was associated with deeper rooting and improved water extraction from the subsoil. No yield increases were recorded with autumn-sown crops which were largely grown on the medium and heavy textured soils. There was a trend towards yield reductions on deep silty soils in wetter years. At one site only did the response to phosphorus and potassium fertilizer incorporated into the subsoil exceed that of fertilizer applied to the topsoil.     

Mitigation of subsoil recompaction by light traffic and on-land ploughing: II. Root and yield response

Plough pans have been shown to severely hamper root development, limit rooting depth and reduce crop yields. We evaluated the effect of plough pan re-compaction on root and yield response for winter wheat in a field trial conducted in two neighbouring fields on a sandy loam. Plots were mechanically loosened by a subsoiler to a depth of 35 cm in 1997 and 1998. In 2 years following the loosening operation, perennial grass/clover was grown with limited traffic intensity. Subsequently oats were established and followed by winter wheat. On-land ploughing was compared with traditional mouldboard ploughing. In addition, the plots were either heavy-trafficked (10–18 Mg axle load and ∼200 kPa inflation pressure) or light-trafficked (<6 Mg axle load and <100 kPa inflation pressure). The loosened treatments were referenced by non-loosened soil. Root growth of winter wheat was followed applying the minirhizotron technique. In one of the fields, these measurements were supplemented with core sampling for root length determination approximately at anthesis. Soil water content was followed in one of the fields using time domain reflectometry (TDR). Grain yield and nitrogen content in grain were determined. The adjoining study showed that the combination of heavy traffic and traditional ploughing caused strong recompaction of loosened soil, whereas the combination of light traffic and on-land ploughing produced moderate recompaction. For the loosened plots in one field, the strongly recompacted soil produced 7% lower yield than moderately recompacted soil, whereas no clear difference was found for the other field. No clear difference between the loosened treatments on root growth was observed. Surprisingly, the non-loosened soil performed similar or even better than the loosened and moderately compacted soil. The non-loosened soil facilitated higher root intensity at depth and produced similar yield and N-uptake. Our results suggest that mechanical subsoil loosening of humid sandy loams only is recommendable in case of very severe subsoil compaction. Natural alleviation of subsoil structure induced by changes in soil management may comprise a favourable alternative to mechanical subsoil loosening.     

Surface-soil responses to paraplowing of long-term no-tillage cropland in the Southern Piedmont USA

The type of conservation-tillage management employed could impact surface-soil properties, which could subsequently affect relationships between soil and water quality, as well as with soil C sequestration and greenhouse gas emissions. We determined soil bulk density, organic C and N fractions, plant-available N, and extractable P on Typic Kanhapludults throughout a 7-year period, in which four long-term (>10 years), no-tillage (NT) water catchments (1.3–2.7 ha each) were divided into two treatments: (1) continuation of NT and (2) paraplowing (PP) in autumn (a form of non-inversion deep ripping) with NT planting. Both summer [cotton (Gossypium hirsutum L.), maize (Zea mays L.), sorghum (Sorghum bicolor L. Moench), soybean (Glycine max L. Merr.)] and winter [wheat (Triticum aestivum L.), barley (Hordeum vulgare L.), rye (Secale cereale L.), crimson clover (Trifolium incarnatum L.)] crops were NT planted throughout the study under each management system. Soil bulk density was reduced with PP compared with NT by as much as 0.15 Mg m⁻³, but the extent of reduction was inversely related to the time lag between PP operation and sampling event. Soil organic C became significantly enriched with time during this study under NT (0.49 Mg C ha⁻¹ year⁻¹), but not under PP, in which poultry litter was applied equivalent to 5.7 Mg ha⁻¹ year⁻¹ to all water catchments. Soil maintained a highly stratified depth distribution of organic C and N fractions and extractable P under both NT and PP. Inability to perform the PP operation in the last year of this study resulted in rapid convergence of soil bulk density between tillage systems, suggesting that PP had <1-year effectiveness on soil loosening. The high energy cost of PP (ca. 30 kW shank⁻¹) and the lack of sustained improvement in surface-soil properties put into question the value of PP for improving upon long-term NT management in sandy loam and sandy clay loam Ultisols of the Southern Piedmont USA, unless large effects on crop yield, water quality, or other ecosystem processes warrant its use.     

Residue management and tillage effects on soil-water storage and grain yield of dryland wheat and sorghum for a clay loam in Texas

Dryland wheat (Triticum aestivum L.) and grain sorghum (Sorghum bicolor (L.) Moench) are often grown using a wheat–sorghum-fallow (WSF) crop rotation on the semiarid North American Great Plains. Precipitation stored during fallow as soil water is crucial to the success of the WSF rotation. Stubble mulch-tillage (SM) and no-tillage (NT) residue management practices reduce evaporation, but the sparse residue cover produced by dryland crops, particularly sorghum, is insufficient to reduce soil crusting and runoff. Subsoil tillage practices, e.g., paratill (PT) or sweep (ST), fracture infiltration limiting soil layers and, when used with residue management practices, may increase soil-water storage and crop growth. Our objectives were to compare the effects of PT to 0.35 m or ST to 0.10 m treatments on soil cone penetration resistance, soil-water storage, and dryland crop yield with NT and SM residue management. Six contour-farmed level-terraced watersheds with a Pullman clay loam (US soil taxonomy: fine, mixed, superactive, thermic Torrertic Paleustoll; FAO: Kastanozems) at the USDA—Agricultural Research Service, Conservation and Production Research Laboratory, Bushland, TX, USA (35°11′N, 102°5′W) were cropped as pairs using a WSF rotation so that each phase of the sequence appeared each year. In 1988, residue management plots received PT or ST every 3 years during fallow after sorghum resulting in five treatments: (i) NT–PT, (ii) NT–NOPT, (iii) NT–ST, (iv) SM–PT, and (v) SM–NOPT. Cone penetration resistance was the greatest in NT plots and reduced with PT after 12, 23, and 31 months. Mean 1990–1995 soil-water storage during fallow after wheat was greater with NT than with SM, but unaffected by PT or ST. Dryland wheat and sorghum grain yields, total water use, and water use efficiency (WUE) were not consistently increased with NT, however, and unaffected by PT or ST tillage. We conclude, for a dryland WSF rotation, that: (1) NT increased mean soil-water storage during fallow after wheat compared to SM, and (2) ST and PT “subsoil” tillage of a Pullman did not increase water storage or yield. Therefore, NT residue management was more beneficial for dryland crop production than subsoil tillage.     

Remediation of subsoil compaction and compaction effects on corn N availability by deep tillage and application of poultry manure in a sandy-textured soil

Subsoil compaction may reduce the availability and uptake of water and plant nutrients thereby lowering crop yields. Among the management options for remediating subsoil compaction are deep tillage and the selection of crop rotations with deep-rooted crops, but little is known of the effects of applications of organic amendments on subsoil compaction. The objectives of this study were to determine the effects of subsoil compaction on corn yield and N availability in a sandy-textured soil and to evaluate the use of deep tillage and surface applications of poultry manure to remediate subsoil compaction. A field experiment planted to corn (Zea mays L.) was conducted from 2000 to 2001 on a Reelfoot fine sandy loam (fine-silty, mixed thermic Aquic Argiudolls) formed in silty alluvium located in southeast Missouri near the Mississippi River. Treatments were arranged in a factorial design with three levels of subsoil compaction and subsoiling and four rates (averaging 0, 6, 11 and 18 Mg ha⁻¹) of poultry manure. Subsoil tillage to a depth of 30 cm had multiple effects, including overcoming a natural or tillage-induced dense layer or pan and increasing volumetric soil water content and crop N uptake, especially in the 2001 cropping year with low early season precipitation. N recovery efficiency (NRE) was significantly higher in the subsoil treatment compared to the highest compaction treatment in 2001. No significant interactions between manure rates and compaction and subsoiling treatments were observed for corn grain and silage yields, N uptake and NRE. Average increases in corn grain yields over all manure rates due to subsoil tillage of compacted soil were 2002 kg ha⁻¹ in 2000 and 3504 kg ha⁻¹ in 2001. Application of poultry manure had a consistent positive effect on increasing grain yields and N uptake in 2000 and 2001 but did not significantly alter measured soil physical properties. The results of this study suggest that deep tillage and applications of organic amendments are management tools that may overcome restrictions in both N and soil water availability due to subsoil compaction in sandy-textured soils.     

Effects of subsoil compaction on yield and yield attributes of wheat in the sub-humid region of Pakistan

The prolonged use of vehicular traffic for farming creates subsoil compaction, which reduces crop yield and deteriorates the physical conditions of the soil. Field experiments were conducted during 2002–2003 and 2003–2004 in Pakistan to study subsoil compaction effects on soil bulk density, total porosity, yield and yield components of wheat. Soil compaction was artificially created at the start of the experiment using 7.0 t roller having length of 1.5 m and diameter of 1.22 m. Treatments consisted of T₁ = control (no compaction), T₂ = two passes of roller, T₃ = four passes of roller, T₄ = six passes of roller. The experiments were arranged in randomised complete block with four replications. Results indicated that subsoil compaction adversely affected the bulk density, total porosity of soil and root length during both the years. Soil compaction increased the bulk density (BD) from 1.37 for T₁ to 1.57, 1.61 and 1.72 Mg m⁻³ whereas decreased the total porosity from 47.3% for T₁ to 40.0, 37.4 and 34.5% for T₂, T₃ and T_4, respectively. Similarly grain yield decreased from 4141.7 for T₁ to 3912.8, 3364.5 and 3010.3 kg ha⁻¹ for T₂, T₃ and T_4, respectively. The deteriorating effect of compaction depended upon the degree of compaction. Subsoil compaction adversely affected the yield and yield attributes of wheat during both years of experiments. The subsoil compaction adversely affected soil physical conditions, which substantially decreased the yield of wheat. Therefore, appropriate measures of periodic chiselling, controlled traffic, conservation tillage, and incorporating of crops with deep tap root system in rotation cycle is necessary to minimize the risks of subsoil compaction.     

Deep tillage management for high strength southeastern USA Coastal Plain soils

Southeastern USA production is limited in Acrisols (Paleudults and Kandiudults) because they have high strengths and low water holding capacities. Production systems with crop rotations or deep tillage before planting were compared with less intensive management. Production systems included double-crop wheat (Triticum aestivum L.) and soybean (Glycine max L. Merr.) that were drilled in 0.19 m-row widths and grown in 15 m wide, 150 m long plots with soils of varying hardpan depths. Treatments included surface tillage (disked or none), deep tillage (paratilled or none), deep tillage with winter fallow and maize (Zea mays L.) in rotation, and disked/deep tillage with an in-row subsoiler where soybean was planted in conventional 0.76 m-wide rows. Cone indices were measured near the ends of each plot (120 m apart) to assess soil strength differences among soil types and among treatments. Cone indices were 1.50 MPa higher for non-deep tilled treatments than for deep tilled treatments and 0.44 MPa higher in wheel-track mid rows than in non-wheel-track mid rows. Cone indices were also 0.28 MPa higher for soils with shallower Bt horizons. Cone indices were not significantly different for subsoiled treatments and paratilled treatments. Rainfall was erratic throughout the 5-year experiment with dry periods lasting more than 2 weeks at a time and with annual totals ranging from 520 to 1110 mm. Wheat yields were 0.67 Mg ha⁻¹ greater for deep-tilled soils (subsoiled and paratilled) than for non-deep-tilled soils. Soybean yields were 0.36 Mg ha⁻¹ greater for paratilled than for subsoiled or non-deep-tilled treatments partly as a result of the more complete disruption of the paratill and partly because paratilled treatments were managed with narrow rows. Yields did not vary significantly among the soil types despite the fact that they had different cone indices. Tillage was a more dominant factor than soil type. For wheat, lower cone indices from tillage led to higher yields. For soybean, management of uniform loosening from deep tillage and narrow rows led to higher yields.     

Rotary subsoiling newly planted winter wheat fields to improve infiltration in frozen soil

Water erosion and runoff can be severe due to poor infiltration through frozen soil in the dryland wheat (Triticum aestivum L.) production region of the inland Pacific Northwest (PNW), USA. For more than 70 years, farmers and researchers have used various methods of subsoiling to reduce runoff and erosion and to improve infiltration and soil moisture storage. The practice and equipment have evolved from chiseling continuous open channels across hillslopes to the rotary subsoiler that pits the soil. Farmers often subsoil wheat stubble after harvest, but do not employ this practice on newly planted winter wheat fields. These fields are especially vulnerable to erosion because of meager residue cover after a year of fallow. A 6-year field study was conducted in eastern Washington to determine the effect of rotary subsoiling in newly planted winter wheat on over-winter water storage, erosion, infiltration, and grain yield. There were two treatments, rotary subsoiling and control. The rotary subsoiler created one 40 cm-deep pit with 4 L capacity every 0.7 m². Natural precipitation did not cause rill erosion in either treatment because of mild winters during the study period. Net change in water stored over winter was significantly (P < 0.05) improved with rotary subsoiling compared to the control in 2 of 6 years. Grain yield was not affected by treatments in any year or when averaged over years. In 2003, we simulated rainfall for approximately 3 h at a rate of 18 mm/h on both subsoiled and control plots to determine runoff and erosion responses on frozen soils. Rotary subsoiling reduced runoff (P < 0.01) by 38%. Rotary subsoiling also significantly reduced erosion (P < 0.01) during the 20–45 min period after runoff had begun. The total quantities of eroded soils were 1.3 and 3.4 Mg/ha for the subsoiled and control treatments, respectively, with inter-rill the dominant erosion process. The average infiltration rate for the control treatment (3.3 mm/h) was half of the rate for the subsoiled treatment (6.6 mm/h), at the end of the 3 h simulation. Rotary subsoiling of newly-planted winter wheat can increase soil moisture stored over-winter and reduce runoff and soil loss on frozen soils, but the benefit of this practice for increasing grain yield has not been proven.     

Soil loosening on permanent raised-beds in arid northwest China

Poor lateral water infiltration into permanently raised beds (PRB) can reduce crop yield and water use efficiency (WUE) in dryland agriculture. Especially for densely planted crops the reduced soil moisture affects seedling emergence and causes slow crop growth. Soil loosening with three different types of cutters was tested to overcome this problem of wide PRB in this study. A field experiment with five treatments (traditional tillage, bed without soil loosening, bed with soil loosening by two-edge cutter, bed with soil loosening by flat cutter and bed with soil loosening by V-shaped cutter) was conducted in the Hexi Corridor, northwest China, on spring wheat in 2005 and 2006. The effects of soil loosening and the performances of the three cutters were assessed based on 2 years of soil moisture, bulk density, temperature, spring wheat growth, yield, WUE, power and fuel consumption data. Soil loosening significantly increased lateral water infiltration and thus improved soil water content by 3–8% to 100 cm depth and soil temperature by 0.2–0.4 °C to 30 cm depth compared to beds without soil loosening on sandy-loam soil in 100 cm wide bed systems. Furthermore, bulk density at 10–20 cm depth was about 7.4% lower for bed with soil loosening treatments than for bed without soil loosening. The best results were achieved by the V-shaped cutter, which at a slight additional fuel consumption of 0.46–0.84 l ha⁻¹ offered the greatest benefits to spring wheat yield and WUE. Spring wheat yields increased by 5% and WUE improved by 38% compared to traditional tillage due to higher soil moisture and temperature, lower bulk density and faster growth. The improvements in WUE have tremendous implications in the arid areas of northwest China where agriculture relies heavily on irrigation, but water resources are scarce. We conclude therefore that soil loosening by V-shaped cutter is an efficient way to remove poor water infiltration, and significantly improve yield and WUE for wide beds under PRB farming system in arid areas of northwest China.     

华北潮土区不同耕作方式下土壤动物丰富度与多样性

在黄淮海平原小麦-玉米一年两熟地区,试验设置了5个处理,分别为玉米小麦每年均翻耕(CTWT)、玉米免耕+小麦每年翻耕(CNTWT)、玉米免耕+小麦每2年翻耕(CNTW2T)、玉米免耕+小麦每4年翻耕(CNTW4T)、玉米小麦每年均免耕(CNTWNT),所有处理的农作物地上秸秆全部移出。调查结果显示,中小型土壤动物在数量上占总数的比例为83%～91%,土壤动物主要分布在表层,占有其总量的71.9%～73.2%。土壤动物存在显著的季节性动态,其丰富度在玉米季高于小麦季。土壤动物Shannon多样性指数在整体上表现为翻耕高于免耕处理,玉米季翻耕处理下有更高的均匀度指数,但小麦季均匀度指数差异不显著。多元典范冗余分析表明,耕作方式主要是对土壤动物的时间动态和垂直分布产生影响,从而间接地影响了土壤动物的数量和组成。     

Hydraulic conductivity, residue cover and soil surface roughness under different tillage systems in semiarid conditions

The objective of this study was to investigate the effect of tillage and cropping system on near-saturated hydraulic conductivity, residue cover and surface roughness to improve soil management for moisture conservation under semiarid Mediterranean conditions. Three tillage systems were compared (subsoil tillage, minimum tillage and no-tillage) under three field situations (continuous crop, fallow and crop after fallow) on two soils (Fluventic Xerochrept and Lithic Xeric Torriorthent). Soil under no-tillage had lower hydraulic conductivity (5.0 cm day⁻¹) than under subsoil tillage (15.5 cm day⁻¹) or minimum tillage (14.3 cm day⁻¹) during 1 of 2 years in continuous crop due to a reduction of soil porosity. Residue cover at sowing was greater under no-tillage (60%) than under subsoil or minimum tillage (<10%) in continuous crop. Under fallow, residue cover was low (10%) at sowing of the following crop for all tillage systems in both soils. Surface roughness increased with tillage, with a high value of 16% and decreasing following rainfall. Under no-tillage, surface roughness was relatively low (3–4%). Greater surface residue cover under no-tillage helped conserve water, despite indications of lower hydraulic conductivity. To overcome the condition of low infiltration and high evaporation when no-till fallow is expected in a cropping sequence, either greater residue production should be planed prior to fallow (e.g. no residue harvest) or surface tillage may be needed during fallow.     

Soil stress as affected by wheel load and tyre inflation pressure

The relative importance of wheel load and tyre inflation pressure on topsoil and subsoil stresses has long been disputed in soil compaction research. The objectives of the experiment presented here were to (1) measure maximum soil stresses and stress distribution in the topsoil for different wheel loads at the same recommended tyre inflation pressure; (2) measure soil stresses at different inflation pressures for the given wheel loads; and (3) measure subsoil stresses and compare measured and simulated values. Measurements were made with the wheel loads 11, 15 and 33 kN at inflation pressures of 70, 100 and 150 kPa. Topsoil stresses were measured at 10 cm depth with five stress sensors installed in disturbed soil, perpendicular to driving direction. Contact area was measured on a hard surface. Subsoil stresses were measured at 30, 50 and 70 cm depth with sensors installed in undisturbed soil. The mean ground contact pressure could be approximated by the tyre inflation pressure (only) when the recommended inflation pressure was used. The maximum stress at 10 cm depth was considerably higher than the inflation pressure (39% on average) and also increased with increasing wheel load. While tyre inflation pressure had a large influence on soil stresses measured at 10 cm depth, it had very little influence in the subsoil (30 cm and deeper). In contrast, wheel load had a very large influence on subsoil stresses. Measured and simulated values agreed reasonably well in terms of relative differences between treatments, but the effect of inflation pressure on subsoil stresses was overestimated in the simulations. To reduce soil stresses exerted by tyres in agriculture, the results show the need to further study the distribution of stresses under tyres. For calculation of subsoil stresses, further validations of commonly used models for stress propagation are needed.     

Tillage, crop residue and N fertilizer effects on crop yield, nutrient uptake, soil quality and nitrous oxide gas emissions in a second 4-yr rotation cycle

An 8-yr (1998–2005) field experiment was conducted on a Gray Luvisol (Boralf) soil near Star City, Saskatchewan, Canada, to determine the effects of tillage (no-tillage – NT and conventional tillage – CT), straw management (straw retained – R and straw not retained – NR) and N fertilizer (0, 40, 80 and 120 kg N ha⁻¹, except no N to pea (Pisum sativum L.) phase of the rotation) on seed and straw yield, mass of N and C in crop, organic C and N, inorganic N and aggregation in soil, and nitrous oxide (N₂O) emissions for a second 4-yr rotation cycle (2002–2005). The plots were seeded to barley (Hordeum vulgare L.) in 2002, pea in 2003, wheat (Triticum aestivum L.) in 2004 and canola (Brassica napus L.) in 2005. Seed, straw and chaff yield, root mass, and mass of N and C in crop increased with increasing N rate for barley in 2002, wheat in 2004 and canola in 2005. No-till produced greater seed (by 51%), straw (23%) and chaff (13%) yield of barley than CT in 2002, but seed yield for wheat in 2004, and seed and straw yield for canola in 2005 were greater under CT than NT. Straw retention increased seed (by 62%), straw (by 43%) and chaff (by 12%) yield, and root mass (by 11%) compared to straw removal for barley in 2002, wheat in 2004, and seed and straw yield for pea in 2003. No-till resulted in greater mass of N in seed, and mass of C in seed, straw, chaff and root than CT for barley in 2002, but mass of N and C were greater under CT than NT for wheat in 2004 and for canola in 2005 in many cases. Straw retention had greater mass of N and C in seed, straw, chaff and root in most cases compared to straw removal for barley in 2002, pea in 2003 and wheat in 2004. Soil moisture content in spring was higher under NT than CT and with R than NR in the 0–15 cm depth, with the highest moisture content in the NT + R treatment in many cases. After eight crop seasons, tillage and straw management had no effect on total organic C (TOC) and N (TON) in the 0–15 cm soil, but light fraction organic C (LFOC) and N (LFON), respectively, were greater by 1.275 Mg C ha⁻¹ and 0.031 Mg N ha⁻¹ with R than NR, and also greater by 0.563 Mg C ha⁻¹ and 0.044 Mg N ha⁻¹ under NT than CT. There was no effect of tillage, straw and N fertilization on the NH₄-N in soil in most cases, but R treatment had higher NO₃-N concentration in the 0–15 cm soil than NR. The NO₃-N concentration in the 0–15, 15–30 and 30–60 cm soil layers increased (though small) with increasing N rate. The R treatment had 6.7% lower proportion of fine (<0.83 mm diameter) and 8.6% greater proportion of large (>38.0 mm) dry aggregates, and 4.5 mm larger mean weight diameter (MWD) compared to NR treatment. This suggests a lower potential for soil erosion when crop residues are retained. There was no beneficial effect of elimination of tillage on soil aggregation. The amount of N lost as N₂O was higher from N-fertilized (580 g N ha⁻¹) than from zero-N (155 g N ha⁻¹) plots, and also higher in CT (398 g N ha⁻¹) than NT (340 g N ha⁻¹) in some cases. In conclusion, retaining crop residues along with no-tillage improved some soil properties and may also be better for the environment and the sustainability of high crop production. Nitrogen fertilization improved crop production and some soil quality attributes, but also increased the potential for NO₃-N leaching and N₂O-N emissions, especially when applied in excess of crop requirements.     

Surface versus incorporated residue effects on water-stable aggregates

Reduced tillage methods for field crop production result in less disruption of soil structure and often increased amounts of crop residue maintained on the soil surface. The combination of these two factors produces increased surface soil aggregation. This study was conducted in the field and within pots to determine whether surface residue by itself improves soil aggregation within a short period of time. The soil was a silt loam loess deposit in the Pacific Northwest, USA, where summers are hot and dry, and most precipitation (420 mm) is received during the mild winters. Two pot studies were conducted over winter, one under a shelter with controlled irrigations (183 mm), and the other outdoors receiving natural precipitation (77 mm). In both pot studies 640 g m⁻² wheat (Triticum aestivum L.) residue was either placed on the surface of the soil or thoroughly mixed into the soil. The field study was conducted on plots where, for the past 7 years, wheat crop residues were either incorporated through chisel/disk tillage or removed before tillage and replaced on the surface after tillage. The field study included plots where wheat was grown with no tillage. In the pots, there was no significant effect due to residue treatment on aggregate mean weight diameter, measured monthly for 4 winter months. This was true despite dissolved organic carbon being leached from the surface residue. In the 7-year-old field plots, replacing residues on the surface resulted in slightly greater mean weight diameter of aggregates at 5–10 cm depth compared to the mixed residue treatment. The no-till plots had significantly greater mean weight diameter at 0–5 cm depth than either tilled treatment. Our conclusion is that surface residue by itself failed to increase aggregation of tilled surface soil within the first rainy season after tillage.     

Crop and soil response to subsoil loosening, deep incorporation of phosphorus and potassium fertilizer and subsequent soil management on a range of soil types.: Part 2: Soil structural conditions

Abstract. In a series of experiments on 16 sites both a power-driven rotary-tine Wye Double Digger and a rigid tine winged subsoiler produced significant subsoil loosening and fissuring. The Double Digger consistently produced the greatest clod breakdown together with the least soil bulk densities and cone penetration resistances. Management strategies after loosening had an important influence on the longevity of the loosening effect. The rate of recompaction was least with controlled traffic and bed systems and increased with random traffic and with the growing of root crops. No significant differences in crop response were monitored between the two loosening treatments, yield response depending largely on the extent of moisture stress experienced by the crop. Loosening on silty soils reduced yields in wet seasons and this was associated with soil structural instability. Visual soil profile examination is necessary to support bulk density and cone penetration resistance measurements when assessing soil compaction.     

Soil organic carbon changes after 12 years of no-tillage and tillage of Grantsburg soils in southern Illinois

Many factors including management history, soil type, climate, and soil landscape processes affect the dynamics of soil organic carbon (SOC). The primary objective of this research was to determine the effects of no-tillage and tillage systems on the SOC content after 12 years of controlled treatments. A tillage experiment with three treatments (no-till (NT), chisel plow (CP) and moldboard plow (MP)) was initiated in the spring of 1989 in southern Illinois. The plot area was previously in a tall fescue hayland for 15 years and had a 6% slope. Maize (Zea mays L.) and soybean (Glycine max L. Merr.) were grown in the plot area on a yearly rotation system starting with maize. Periodically, the SOC content of various soil layers, to a depth of either 30 or 75 cm, was measured and expressed on both a gravimetric and volumetric basis. After 12 years, the 0–15 cm surface soil layer of MP was significantly lower in SOC than the NT and CP plots. For all but 2 values, the significance of findings did not change with the form of expression (gravimetric versus volumetric). The surface layer (0–15 cm), subsoil (15–75 cm), and rooting zone (0–75 cm) of all treatments had reduction in SOC on a volumetric basis when compared to the pre-treatment values for sod. At the end of the 12-year study, the MP system had significantly less SOC in the surface layer, subsurface layer and rooting zone than the NT system at comparable depths. After 12 years of tillage under a maize–soybean rotation, the NT treatment sequestered or maintained more SOC stock (47.0 Mt ha⁻¹) than the CP (43.7 Mt ha⁻¹) and MP (37.7 Mt ha⁻¹) treatments. The annual rate of SOC stock build up in the root zone (0–75 cm), above the MP system base, was 0.71 Mt ha⁻¹ year⁻¹ for the NT system and 0.46 Mt ha⁻¹ year⁻¹ for the CP system. For land coming out of the Conservation Reserve Program and returning to row crop production, NT and CP systems would maintain more SOC stock than MP system and reduce CO₂ emissions to the atmosphere.     

The effect of subsoiling on soil resistance and cotton yield

Soil compaction occurs due to heavy wheeling or repetitive tillage in the field. Soil compaction changes the soil physical parameters and water infiltration that cause reduction in the crop yield. Proper subsoiling alleviates the negative effect of soil compaction. The objectives of the research was to examine the effects of subsoiling on the resistance of the soil and to find out deep tillage effects on the cotton yield and the convenient time for applying subsoil treatment for reducing the soil compaction. One-pass (B) and two-passes (C) subsoil treatments were applied in the fields where wheat, silage maize (Zea mays L.) and cotton (Gossypium hirsutum L.) crops were grown by 2 years rotation. The experiment was started in 1998 and carried out for 4 years. Soil penetrations were measured during the experiments years at thaw conditions of silty-clay soil (43% clay, 50% silt, 7% sand) before seedbed preparation in autumn seasons. According to the results, the subsoiling treatments created statistically significant effects on the soil resistance (P<0.05) comparing the control plots (A). The initial disruption in subsoiled plots has almost disappeared after 2 and 4 years in B and C plots, respectively. The soil resistance in C plots was lower than in B plot. The percentage of decrease in the soil resistance from A to B and A to C plots was calculated as 13.3 and 26.2%, respectively, in the first year. In the effective subsoiling area from 0.20 to 0.50 m depth, the ratio of penetration decrease in both plots was about 7–8% per year. The difference of penetration decrease between B and C plots was found to be about 15.8% level. Cotton yields at each subsoiled plots increased slightly comparing with control plots (A) where subsoiling was not applied. However, these increments were found to be statistically insignificant. It may be concluded that the subsoiling treatments does not affect the crop yield in intensive and fully irrigated field conditions.