Effect of tillage practices on wheat performance in a semi-arid environment

Sodosol soils are at risk of degradation under existing fallow management practices involving tillage. Topsoil erosion exposes horizons with reduced infiltration and low concentrations of plant nutrients. Conservation management systems are needed on these soils to avoid a reversion to low intensity grazing. This paper reports on a 4 year study (1986–1989) of the effects of tillage practices on profile soil water and crop yield in a Sodosol (Typic Natrustalf) in central Queensland, Australia. The tillage treatments were: zero till fallow (weed control by herbicides), reduced till fallow (chisel plough/scarifier or herbicides) and conventional till fallow (chisel plough/scarifier) in two linked experiments. In the first experiment, wheat was grown in three contour bays (approximately 1 ha), and in the second, wheat was grown in replicated plots (30 m × 6 m) to allow statistical comparisons.

Zero till provided consistent advantages in grain yield in all 4 years compared with conventional till. Zero till also outyielded reduced till as well as conventional till in the plot experiment. The average yield increase of 0.5 t ha⁻¹ in zero till compared with convention till was associated with greater water use and increased water use efficiency. Tillage practice caused only marginal differences in the available water content in the root zone (0–100 cm) at sowing; zero and reduced till contained, on average, an additional 4 and 8 mm, respectively, compared with conventional till. The tillage treatments had no effect on plant available water capacity. Some of the soil water that accumulated during the fallow drained beyond the root zone in all treatments and was not available to the following wheat crop. At the conclusion of the experiment, soil water accumulation in the 100–180 cm soil layer was 86 mm in zero till, 39 mm in reduced till and 40 mm in conventional till.

Results indicate that zero till can be a more productive wheat farming practice than conventional mechanical tillage. The increase in water storage below the root zone of the wheat crop shows that there may be benefit in using a deeper-rooting crop or pasture species in rotation with wheat, particularly after zero till fallows.     

Effects of tillage systems and rotations on crop production for a thin Black Chernozem in the Canadian Prairies

Soil degradation is the single most important threat to global food production and security. Wind and water erosion are the main forms of this degradation, and conservation tillage represents an effective method for controlling this problem. The objective of this study was to quantify the effects of three tillage methods [zero (ZT), minimum (MT) and conventional (CT)] and three four-year crop sequences [spring wheat (Triticum aestivum L.)–spring wheat–winter wheat–fallow; spring wheat–spring wheat–flax (Linum usitatissimum L.)–winter wheat; spring wheat–flax–winter wheat–field pea (Pisum sativum L.] on crop establishment, plant height, seed weight, soil water storage, crop water use, crop water use efficiency and grain yield over a 12-year period under Canadian growing conditions. Plant establishment was not adversely affected by tillage systems or crop sequences except for flax, where a small reduction was observed with ZT and MT. Conservation tillage showed a yield benefit over CT of 7%, 12.5% and 7.4% for field pea, flax and spring wheat grown on cereal stubble, respectively over the 12 years of the study. Much of the yield increase was due to an increase in soil water in the 0–30 cm soil layer with ZT and MT. However, tillage systems had no effect on grain yield for spring wheat grown on fallow and field pea stubble due to a lack of differences in spring soil water content. Flax grown in sequence with cereals only yielded higher than when it was grown in the sequence which included field pea, even though flax was seeded on spring wheat stubble in both cases. Winter wheat yielded higher when grown on flax stubble than on spring wheat stubble. The results indicate that a one-year non-cereal break crop was enough to alleviate the negative effects of consecutive cereal crops on winter wheat. Spring wheat grown on field pea stubble always yielded more than when grown on cereal stubble. A 10% increase in water use efficiency was observed with flax grown with ZT and MT management. Crop sequence improved water use efficiency in flax and spring wheat. Growing spring wheat on field pea stubble as opposed to growing it on cereal stubble resulted in a 10% increase in water use efficiency. Overall, rainfall accounted for 73%, 72%, 67% and 65% of total water used by field pea, flax, winter wheat and spring wheat, respectively. This explains the large year effect as a result of variation in growing (May–August) season precipitation. The non-significant tillage system by year interaction implies that the positive benefits of ZT and MT occur over a wide range of growing conditions, while the absence of a tillage system by crop sequence interaction suggests that knowledge developed under CT management also applies to ZT and MT. The results of this study support the large shifts towards in conservation tillage being observed in the Canadian prairies.     

Changes in total, mineralizable and light fraction soil organic matter with cropping and tillage intensities in semiarid southern Alberta, Canada

There has been a trend toward increased cropping intensity and decreased tillage intensity in the semiarid region of the Canadian prairies. The impact of these changes on sequestration of atmospheric CO₂ in soil organic carbon (C) is uncertain. Our objective was to quantify the changes in total, mineralizable and light fraction organic C and nitrogen (N) due to the adoption of continuous cropping and conservation tillage practices. We sampled three individual long-term experiments at Lethbridge, Alberta, in September 1992: a spring wheat (Triticum aestivum L.)-fallow tillage study, a continuous spring wheat tillage study and a winter wheat rotation-tillage study. Treatments had been in place for 3–16 years. In the spring wheat-fallow study, different intensities (one-way disc > heavy-duty cultivator > blade cultivator) of conventional tillage (CT) were compared with minimum tillage (MT) and zero tillage (ZT). After 16 years, total organic C was 2.2 Mg ha⁻¹ lower in more intensively worked CT treatments (one-way disc, heavy-duty cultivator) than in the least-intensive CT treatment (blade cultivator). The CT with the blade cultivator and ZT treatments had similar levels of organic C. The CT treatments with the one-way disc and heavy-duty cultivator had light fraction C and N and mineralizable N amounts that were about 13–18% lower than the CT with the blade cultivator, MT or ZT treatments. In the continuous spring wheat study, 8 years of ZT increased total organic C by 2 Mg ha⁻¹, and increased mineralizable and light fraction C and N by 15–27%, compared with CT with a heavy-duty cultivator prior to planting. In the winter wheat rotation-tillage study, total organic C was 2 Mg ha⁻¹ higher in a continuous winter wheat (WW) rotation compared with that in a winter wheat-fallow rotation. The lack of an organic C response to ZT on the WW rotation may have been due to moldboard plowing of the ZT treatment in 1989 (6 years after establishment and 3 years before soil sampling), in an effort to control a severe infestation of downy brome (Bromus tectorum L.). Our results suggest that although relative increases in soil organic matter were small, increases due to adoption of ZT were greater and occurred much faster in continuously cropped than in fallow-based rotations. Hence intensification of cropping practices, by elimination of fallow and moving toward continuous cropping, is the first step toward increased C sequestration. Reducing tillage intensity, by the adoption of ZT, enhances the cropping intensity effect.     

Diversified cropping systems in semiarid Montana: Nitrogen use during drought

Improved nitrogen use efficiency would be beneficial to agroecosystem sustainability in the northern Great Plains of the USA. The most common rotation in the northern Great Plains is fallow–spring wheat. Tillage during fallow periods controls weeds, which otherwise would use substantial amounts of water and available nitrogen, decreasing the efficiency of fallow. Chemical fallow and zero tillage systems improve soil water conservation, and may improve nitrogen availability to subsequent crops. We conducted a field trial from 1998 through 2003 comparing nitrogen uptake and nitrogen use efficiency of crops in nine rotations under two tillage systems, conventional and no-till. All rotations included spring wheat, two rotations included field pea, while lentil, chickpea, yellow mustard, sunflower, and safflower were present in single rotations with wheat. Growing season precipitation was below average in 3 of 4 years, resulting in substantial drought stress to crops not following fallow. In general, rotation had a greater influence on spring wheat nitrogen accumulation and use efficiency than did tillage system. Spring wheat following fallow had substantially higher N accumulation in seed and biomass, N harvest index, and superior nitrogen use efficiency than wheat following pea, lentil, chickpea, yellow mustard, or wheat. Preplant nitrate-N varied widely among years and rotations, but overall, conventional tillage resulted in 9 kg ha⁻¹ more nitrate-N (0–60 cm) for spring wheat than did zero tillage. However, zero tillage spring wheat averaged 11 kg ha⁻¹ more N in biomass than wheat in conventional tillage. Nitrogen accumulation in pea seed, 45 kg ha⁻¹, was superior to that of all alternate crops and spring wheat, 17 and 23 kg ha⁻¹, respectively. Chickpea, lentil, yellow mustard, safflower, and sunflower did not perform well and were not adapted to this region during periods of below average precipitation. During periods of drought, field pea and wheat following fallow had greater nitrogen use efficiency than recropped wheat or other pulse and oilseed crops.     

Tillage and crop residue management affect vertisol properties and grain sorghum growth over seven years in the semi-arid sub-tropics. 1. Crop residue and soil water during fallow periods

The effects of fallow surface management treatments on stubble (crop residue) levels and soil water storage were studied during seven fallow periods between grain sorghum crops on a grey Vertisol near Biloela in central Queensland, Australia. Treatments were disc (D), blade (B) and zero (Z) tillage, each with stubble or residue from preceding crops either retained (+) or removed (-) at the start of the fallow periods, which were of 7–8 months duration.

Where stubble was retained, stubble dry matter levels on the soil surface at the start of the fallow period were mainly influenced by stubble produced by the previous crop, but also by residual stubble on the soil surface before the previous crop. The general order was D +< B +< Z+.

Stubble dry matter and stubble cover on the soil surface declined during the fallow period in all stubble-retained treatments, with the greatest reductions occurring after the initial disc or blade tillage. From the start to end of the fallow, mean reductions in stubble dry matter and stubble cover were, respectively, 60 and 74% in D+, 31 and 57% in B+, and 17 and 24% in Z+. Mean stubble dry matter levels on the soil surface at the end of the fallow period in December–January were 1030, 2030 and 2910 kg ha⁻¹ in D+, B+ and Z+, respectively; corresponding stubble cover levels were 8, 16 and 35%.

Mean plant available water capacity to 1.8 m was 201 mm. Mean fallow soil water accumulation varied between fallow periods from 11 to 102 mm. The corresponding variation in mean fallow water storage efficiency (percentage of rainfall over the fallow stored in the soil) was from 3 to 37%. Fallow soil water accumulation was significantly (P<0.05) higher in Z+ (116 mm) than in Z- (86 mm), D+ (96 mm) and D- (84 mm) in one fallow period.

During the fallow period, B+ and Z+ generally resulted in higher plant available water than other treatments at mean values of 50–100 mm. However, these effects were not present at higher plant available water levels (mean of 128–164 mm), as occurred at the end of six fallow periods. The main treatment effect at the end of the fallow was for significantly (P<0.05) lower plant available water in Z-.     

Short-term responses of soil physical properties to corn tillage-planting systems in a humid maritime climate

The fertile, but naturally poorly drained soils of the western Fraser Valley in British Columbia, Canada are located in an area subject to about 1200 mm of rainfall annually. These soils were under intensive conventional tillage practices for years, which contributed to their poor infiltrability, low organic matter, and overall poor structure. Development of tillage practices that incorporate winter cover crops and reduce traffic in spring is required to reduce local soil degradation problems. The objective of this study was to determine short-term responses of soil physical properties to fall and spring tillage (ST) and fall and no spring tillage (NST) systems, both using spring barley (Hordeum vulgare L.) and winter wheat (Triticum aestivum L.) as winter cover crops. Field experiments were conducted for 3 years following seeding of the winter cover crops in fall 1992 on a silty clay loam Humic Gleysol (Mollic Gleysol in FAO soil classification). Average aeration porosity was 0.15 m³ m⁻³ on NST and 0.22 m³ m⁻³ on ST, while bulk density was 1.22 Mg m⁻³ on NST and 1.07 Mg m⁻³ on ST at the 0–7.5 cm depth. Neither of these two soil properties should limit seedling and root growth. After ST, mechanical resistance was consistently greater for 500–1000 kPa in NST than in ST, but never reached value of 2500 kPa considered limiting for root growth. The NST system did not increase soil water content relative to ST, with soil water contents being similar at 10 and 40 cm depth in all years. In 2 out of 3 years NST soil was drier at the 20 cm depth than was ST soil. Three years of NST did not result in a significant changes of aggregate stability relative to ST. This experiment showed that limiting tillage operations to the fall did not adversely affect soil physical conditions for plant growth in a humid maritime climate.     

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.     

The role of tillage and crops on a soil loss of an arable Stagnic Luvisol

The poor physical, chemical and biological properties make Stagnic Luvisol highly susceptible to water erosion on sloping terrains. The objective of this paper is to estimate the effect of different tillage treatments and crops (maize, soybean, winter wheat, spring barley, oilseed rape) on water erosion. The highest erosion in investigation period (1995–2014) was recorded in the control treatment with fallow, followed by the treatment that involved ploughing and sowing up and down the slope. Significantly, lower soil losses were recorded in no-tillage and treatments with ploughing and sowing across the slope. Regarding the crops significantly higher soil losses were recorded in spring row crops (maize and soybean) compared to high-density winter crops (wheat and oilseed rape) and double crop (spring barley with soybean). In the studied period, an average loss of 46 mm of the plough layer was recorded in the control treatment, while in treatment with ploughing and sowing up and down the slope average annual soil loss was 10 mm. According to the results of this study no-tillage and tillage across the slope are recommended as tillage which preserves soil for the next generations in agro-ecological conditions of continental Croatia.     

Wheel traffic and tillage effects on runoff and crop yield

Traffic and tillage effects on runoff, soil water and crop production under rainfall were investigated over a period of 6 years on a heavy clay vertosols (vertisols) in Queensland, Australia. A split plot design was used to isolate traffic effects, while the cropping program and treatments were broadly representative of extensive grain production practice in the northern grain region of Australia. Treatments subject to zero tillage and stubble mulch tillage each comprised pairs of 90 m² plots, from which runoff was recorded. A 3 m wide controlled traffic system allowed one of each pair to be maintained as a non-wheeled plot, while the complete surface area of the other received a single annual wheeling treatment from a working 100 kW tractor.

Mean annual runoff from controlled traffic plots was 81 mm (36.3%) smaller than that from wheeled plots, while runoff from zero tillage was reduced by 31 mm (15.7%). Traffic and tillage effects appeared to be cumulative, so the mean annual runoff from controlled traffic and zero tillage plots, representing best practice, was 112 mm (47.2%) less than that from wheeled stubble mulch plots, representing conventional cropping practice. Rainfall infiltration into controlled traffic zero tillage soil was thus 12.0% greater than into wheeled stubble mulched soil. Rainfall/runoff hydrographs show that wheeling produced a large and consistent increase in runoff, whereas tillage produced a smaller increase. Treatment effects were greater on dry soil, but were still present in large and intense rainfall events on wet soil.

Plant available water capacity (PAWC) in the 0–500 mm zone increased by 10 mm (11.5%) and mean grain yields increased by 337 kg/ha (9.4%) in controlled traffic plots, compared with wheeled plots. Mean grain yield of zero tillage was 2–8% greater than that of stubble mulch plots for all crops except for winter wheat in 1994 and 1998. Increased infiltration and plant available water were probably responsible for increased mean grain yields of 497 kg/ha (14.5%) in controlled traffic zero tillage, compared with wheeled stubble mulch treatments. Dissipation of tractive and tillage energy in the soil is the apparent mechanism of deleterious effects on the soils ability to support productive cropping in this environment. Controlled traffic and conservation tillage farming systems appear to be a practicable solution.     

Effects of three soil tillage systems on some biological activities in an Ultisol from southern Chile

Intensive tillage for annual crop production may be affecting soil health and quality. However, tillage intensity effects on biological activities of volcanic-derived soils have not been systematically investigated. We evaluated the effects of three different tillage practices on some biological activities of an Ultisol from southern Chile during the third year of a wheat–lupin–wheat crop sequence. Treatments were: no tillage with stubble burning (NTB), no tillage without stubble burning (NT) and conventional tillage with disk-harrowing and stubble burning (CT). Biological activities were evaluated in winter and summer at 0–200 mm and at three soil depths (0–50, 50–100 and 100–200 mm) in winter. Total organic C and N were significantly higher under no-tillage systems than CT. In general, NT increased C and N of microbial biomass in comparison with CT, especially in winter. Microbial biomass C was closely associated with microbial biomass N (r = 0.986, P < 0.05); acid phosphomonoesterase (r = 0.999, P < 0.05); β-glucosidase (r = 0.978, P < 0.05), and others. Changes in biological activities occurred mainly in the upper soil layer (0–50 mm depth) in spite of the short duration of the experiment. Biological activities could be used as practical biological indicators to apply the more appropriate management systems for increasing soil sustainability or productivity.     

坡面水土保持措施的减沙水代价分析

水土保持措施在减少土壤侵蚀的同时也会减少地表径流,减沙水代价可以直观说明不同措施同步影响径流和泥沙的差异。根据黄土高原沟壑区西峰、天水的农地径流场多年观测资料,统计分析不同耕作措施及生物措施的减沙水代价。结果表明:不同耕作措施和生物措施减沙水代价受最大30 min降雨强度(I30)和坡度影响较大,呈显著负相关;对于耕作措施和生物措施,当I30分别大于0.29和0.48 mm/min时,坡度与措施减沙水代价表现出较好的指数函数关系;耕作措施减沙水代价表现为防冲沟>浅耕>深耕,防冲沟较深耕高33.8%;各生物措施减沙水代价表现为低秆作物和高秆作物玉米/黄豆间作>单作低秆作物扁豆>中高秆作物冬小麦/荞麦轮作。     

Soil organic matter and related physical properties in a Mediterranean wheat-based rotation trial

Under semi-arid Mediterranean conditions, limited moisture is the main constraint to rainfed cropping with wheat (Triticum aestivum), barley (Hordeum vulgare), and food and forage legumes. With increasing land-use pressure, moisture-conserving fallowing is being replaced by continuous cropping, which is considered an unsustainable practice. Thus, a long-term trial with durum wheat (T. turgidum var. durum) was established in 1983 at Tel Hadya, Aleppo, Syria (mean annual rainfall 330 mm) to assess alternative rotation options to fallow and continuous cropping. Nitrogen (N) and grazing/residue management were secondary factors. Soil aggregation, infiltration, hydraulic conductivity, and total soil organic matter and component fractions (fulvic and humic acids and polysaccharides) were determined at the end of 12 years. Some rotations, e.g., medic (Medicago sativa) and vetch (Vicia faba), significantly increased soil organic matter (12.5–13.8 g kg⁻¹ versus 10.9–11 g kg⁻¹ for continuous wheat and wheat/fallow). All measurements, or indices, indicated parallel trends with increasing organic matter, e.g., coefficients of macro-structure, micro-aggregation, and water-stable aggregates, and decreasing dispersion. Similarly, legume rotations had higher infiltration rates (16.2–21.8 cm h⁻¹ versus 13.9–14.4 cm h⁻¹ with continuous wheat and wheat/fallow) and hydraulic conductivity rates (8.7–12.4 cm h⁻¹ versus 6.2–7.4 cm h⁻¹ with continuous wheat and wheat/fallow). We conclude that cereal/legume rotations, in addition to being biologically and economically attractive, also enhance soil quality and thus promote soil use sustainability in fragile semi-arid areas as in the Mediterranean zone.     

旱作麦田保护性耕作蓄水保墒和增产增收效应

为了揭示渭北旱塬连作麦田不同保护性耕作措施下土壤蓄水保墒效果和冬小麦增产增收效应。于2007－2009年通过田间试验研究了渭北旱塬夏闲期免耕、深松和翻耕等3种耕作方式对麦田夏闲期蓄水保墒效果,以及3种耕作处理与平衡施肥、常规施肥和低肥等3种施肥处理组合对冬小麦生育期土壤水分动态、产量和经济效益的影响。免耕和深松较翻耕保墒作用好,夏闲期免耕、深松较翻耕0～300 cm土层3 a平均土壤含水率分别增加了0.6和0.5个百分点,平均贮水量分别增加了24.2和21.5 mm;生育期内平衡施肥免耕、深松较翻耕处理0～200 cm土层2 a平均土壤贮水量分别增加了17.7和14.4 mm;以平衡施肥深松处理产量最高,2 a平均产量高达5033.1 kg/hm2,较平衡施肥翻耕和平衡施肥免耕分别增产5.5%和6.3%;以平衡施肥免耕经济效益最高,2 a平均纯收益高达5 553.7元/hm2,较平衡施肥深松和平衡施肥翻耕分别增收3.3%和9.2%。综合考虑各处理土壤蓄水保墒效果和小麦增产增收效应,平衡施肥深松处理是渭北旱塬连作麦田较佳的耕作和施肥处理组合。     

Long-term effects of tillage systems and rotations on soil structural stability and organic carbon stratification in semiarid central Spain

Under semiarid Mediterranean climatic conditions, soils typically have low organic matter content and weak structure resulting in low infiltration rates. Aggregate stability is a quality indicator directly related to soil organic matter, which can be redistributed within soil by tillage. Long-term effects (1983–1996) of tillage systems on water stability of pre-wetted and air dried aggregates, soil organic carbon (SOC) stratification and crop production were studied in a Vertic Luvisol with a loam texture. Tillage treatments included conventional tillage (CT), minimum tillage (MT) and zero tillage (ZT) under winter wheat (Triticum aestivum L.) and vetch (Vicia sativa L.) rotation (W–V), and under continuous monoculture of winter wheat or winter barley (Hordeum vulgare L.) (CM). Aggregate stability of soil at a depth of 0–5 cm was much greater when 1–2 mm aggregates were vacuum wetted prior to sieving (83%) than when slaked (6%). However, slaking resulted in tillage effects that were consistent with changes in SOC. Aggregate stability of slaked aggregates was greater under ZT than under CT or MT in both crop rotations (i.e., 11% vs. 3%, respectively).

SOC under ZT tended to accumulate in the surface soil layer (0–5 and 5–10 cm) at the expense of deeper ones. At depths of 10–20 and 20–30 cm no differences in SOC were encountered among tillage systems, but CT exhibited the highest concentration at 30–40 cm depth. Nevertheless, when comparisons were made on mass basis (Mg ha⁻¹), significant differences in stocked SOC were observed at depths of 0–10 and 0–20 cm, where ZT had the highest SOC content in both rotations. The stock of SOC to a depth of 40 cm, averaged across crop rotations, was greater under ZT (43 Mg ha⁻¹) than under CT (41 Mg ha⁻¹) and MT (40 Mg ha⁻¹) although these figures were not significantly different. Likewise, no significant differences were encountered in the stock of SOC to a depth of 40 cm among crop rotations (i.e., 42 Mg ha⁻¹ for W–V vs. 40 Mg ha⁻¹ for CM).

Crop production with wheat–vetch and continuous cereal showed no differences among tillage systems. Yields were strongly limited by the environmental conditions, particularly the amount of rainfall received in the crop growth season and its distribution. Similar yield and improved soil properties under ZT suggests that it is a more sustainable system for the semiarid Mediterranean region of Spain.     

Response of conservation tillage sorghum to growing season precipitation

In earlier crop rotation studies in which grain sorghum (Sorghum bicolor (L.) Moench) followed winter wheat (Triticum aestivum L.) after a 10- to 11-month fallow period during which the wheat residues were managed by different tillage methods, sorghum yields increased in response to increases in soil water content at sorghum planting time. Similar results were obtained when residues were placed on the surface at the start of the fallow period. The soil water contents at planting time were positively correlated with amounts of wheat residue maintained on the soil surface during fallow.

The studies also suggested that sorghum responded positively to growing season precipitation when increasing of residue remained on the soil during the growing season. The objective of this study was to evaluate this response to growing season precipitation through statistical analyses of data from five earlier tillage and residue placement studies. Regression analyses of data from the studies showed that sorghum grain yields increased with increasing amounts of surface residues at planting time. Differences in response of grain yield to precipitation were greatest in the vegetative period. For the period, grain yields increased 0.014 Mg ha⁻¹ per mm of precipitation when residue amounts ranged from 0 to 0.4 Mg ha⁻¹ per mm of precipitation when residue amounts ranged from 0 to 0.4 Mg ha⁻¹, and 0.027 Mg ha⁻¹ per mm of precipitation when residue amounts were 3.2 Mg ha⁻¹.

Differences in response to rainfall in the heading and grain filling period were lower or negligible. High responses for the vegetative period were attributed to the residues which increased infiltration and reduced evaporation before canopy development. Lower responses during heading and lack of responses during grain filling were attributed to: (1) canopy development, which minimized the effect of residues on imfiltration and evaporation; (2) soil cracking, which resulted in similar infiltration with all treatments; and (3) residue decomposition, which minimized differences among residue amounts on the soil with different treatments.     

Seasonal changes in surface aggregate stability under different tillage and crops

Temporal changes in the surface aggregate stability of an Oxic Paleustalf under different tillage practices (direct drilled/stubble retained versus conventional cultivated/stubble burnt) and under different crops (wheat (Triticum aestivum L.) versus lupin (Lupinus angustifolius L.)) were monitored at a 10-year-old rotation site in Wagga Wagga, N.S.W., Australia.

Seasonal fluctuations in aggregate stability were observed under all treatments and were greater than the differences detected between the different tillage and cropping treatments. The seasonal variation was significantly related to the soil water content at the time of sampling and the lowest stability occurred during the autumn/winter period. Cropping under direct drilling and stubble retention resulted in significantly higher stability and lower seasonal fluctuations in stability than under conventional tillage and stubble burning. Despite the seasonal fluctuation, water stability over the season of both of the macroaggregate (more than 250 μm) and microaggregate (less than 50 μm) fractions increased significantly.

While the mean (temporal) stability of the different treatments was significantly related to the mean organic carbon content (r = 0.91) and polysaccharide content, the temporal changes were not related to the soil organic carbon content nor the living root length density.

Lupin had a more beneficial effect on promoting macroaggregate stability than wheat under the conventional tillage/stubble burnt treatment but no significant difference was found under the direct drilled/stubble retained treatment.     

不同绿肥和覆膜措施对渭北旱塬冬小麦产量和土壤水分动态的影响

  【目的】  冬小麦—绿肥轮作在干旱贫水年份易导致冬小麦减产,我们研究了平水年和干旱年旱地绿肥和覆膜措施相结合对小麦产量及水分利用率的影响,为建立科学高效的小麦–绿肥轮作体系奠定基础。  【方法】  田间试验于2017—2019年布设在陕西省永寿县御驾宫乡御中村,试验采用裂区试验设计,以轮作不同绿肥品种(黑麦豆、油菜,夏休闲为对照)为主处理,覆膜措施为副处理,设常规耕作和垄覆沟播两个水平。在冬小麦返青期、开花期、收获期调查小麦苗期生长状况、产量形成、水分利用效率和麦田0—200 cm土壤水分动态变化。  【结果】  1)平水年和干旱年,轮作油菜的冬小麦产量高于轮作黑麦豆,两年间轮作油菜处理比轮作黑麦豆处理的冬小麦产量分别高出 9.3%和43.5% (P<0.05)。2)采用垄覆沟播,轮作绿肥显著降低了冬小麦生育期耗水量,平水年提高了冬小麦的水分利用效率。平水年轮作油菜的水分利用效率最高[14.3 kg/(hm2·mm)],比夏休闲处理增加了7.4%;而干旱年轮作绿肥降低了冬小麦的水分利用效率,与夏休闲相比轮作黑麦豆和油菜处理分别降低58.5%和38.3% (P<0.05)。轮作绿肥与垄覆沟播对提高小麦水分利用效率有显著的交互作用。3)轮作绿肥并垄覆沟播的栽培模式加重了土壤水分的消耗。相比于夏休闲,平水年冬小麦播前0—200 cm土壤贮水量平均降低10.1% (P<0.05),干旱年平均降低15.7% (P<0.05)。  【结论】  我国渭北旱塬地区在平水年采用种植油菜+垄覆沟播新型种植模式,可以在保证不减产的情况下提高冬小麦的水分利用效率,但干旱年小麦产量和水分利用效率均会受到负面影响。     

Long-term impact of conservation tillage on stratification ratio of soil organic carbon and loss of total and active CaCO3

Under semi-arid conditions, the properties of many soils are influenced by the presence of organic matter and calcium carbonate (CaCO₃). However, the influence of different tillage systems on the development of these properties has scarcely been studied under semi-arid Mediterranean conditions. We studied the effect of long-term conservation tillage (CT) and traditional tillage (TT) on the stratification ratio of soil organic carbon and on CaCO₃ content. The study was conducted in a wheat (Triticum aestivum L.)–sunflower (Helianthus annuus L.) crop rotation established in 1991 under rainfed conditions in Southwestern Spain. As is traditional in this area, wheat was fertilised, but sunflower was not. Conservation tillage was characterised by reduced number of tillage operations and leaving crop residues on the soil surface, while TT was with mouldboard ploughing. Stratification ratio of soil organic C was calculated from C contents in the 0–5 and 5–10 cm soil layers divided by that in the 25–40 cm. Stratification ratio of soil organic C under the CT (>2) was significantly greater than under TT (<2); values >2 indicating better soil quality. Our results show a loss of CaCO₃ under both tillage systems. However, the loss of CaCO₃ was significantly higher under TT than under CT. Also, P and K accumulated in the soil surface and stratification ratio for both nutrients was greater in CT than in TT.     

Conservation tillage for soybean in the U.S. Southeastern Coastal Plain

Double cropping of soybean has progressed less rapidly in the U.S. Southeastern Coastal Plains than expected by the ample rainfall and long frost-free season. Post-emergence herbicides, the management of plant residues to reduce water use by cover crops, and a no-till planter with a combination subsoiler are the innovations that have facilitated this new production. Full-season soybean (Glycine max L.) was planted following a grazed cover crop of winter rye (Secale cereale L.) or late-season soybean was planted following winter wheat harvest. In both cases, a special planter was used with an integral subsoil shank ahead of the opener. Full-season soybean under conservation tillage produced yields equal to or better than yields in conventional clean tillage. In a dry summer, soybean yields under conservation tillage exceeded conventional tillage because of suppressed early biomass production which conserved stored soil water and favored growth during the reproduction phase of the crop-cycle. Late-season soybean yields behind wheat favored the conservation tillage practice of in-row subsoil-planting into stubble. However, planting in burned-off wheat stubble produced the highest yields in this study. In a dry spring, the cover crop accelerated soil water use which resulted in lower soybean yields under conservation tillage. Comparisons of 76 vs. 97 cm row spacing were inconclusive, but the trend suggests that wider rows conserve water under periods of drought and that the narrower-row configuration favors adequate water regimes.     

Soil biotic and biochemical factors in a long-term tillage and stubble management experiment on a vertisol. 1. Seedling inhibition by stubble

In a long-term experiment on a vertisol in southern Queensland, depression of vegetative growth of barley (Hordeum vulgare L.) by stubble retention was far greater with zero tillage than with mechanical tillage of the fallow. The possible phytotoxic effects of stubble on barley and wheat (Triticum aestivum L.) were investigated in seedling bioassays. Stubble collected from field plots just prior to planting did not reduce germination of wheat or barley seed but markedly reduced coleoptile length at 4 days. This effect of stubble became less apparent after 6 and 8 days, and was overcome by increasing water volume in the bioassay dish. Stubble absorbed 4.5–6 times its own weight of water and thereby competed with the germinating seed. Filtrates of stubble macerates in water, collected either before or after incubation of the saturated stubble, had no effect on coleoptile length indicating the absence of a water-soluble phytotoxin.

Brown lesions on wheat coleoptiles (most apparent at 8 days) and roots were decreased by stubble but increased by more water in the bioassay dish. Alternaria sp. and two types of bacteria were associated with the coleoptile lesions, and Fusarium sp. and several types of bacteria were associated with root lesions. Surface sterilisation of seed reduced root lesions but not coleoptile lesions. Filtrates of both incubated and unincubated stubble macerates reduced coleoptile lesions.

Poor early growth of barley in the field on zero-till, stubble-retained plots was not associated with incorporation of stubble into the drill slit in contact with the seed. Poor early growth was not overcome by nitrogen fertilizer drilled into the soil 2 months before planting. The quantities of air-dried stubble on the soil surface were capable of absorbing of the order of 4 mm rainfall. It is concluded that neither phytotoxins nor water absorption by the stubble were likely causes of the problem of poor early growth.