Twenty years of conservation tillage research in subarctic Alaska: II. Impact on soil hydraulic properties

Soil management practices are needed in the subarctic that stabilize the soil against the forces of wind and water as well as conserve soil water for crop production. There is a paucity of information, however, regarding the long-term effects of conservation tillage on soil hydraulic properties in subarctic Alaska. The objective of this study was therefore to characterize infiltration, water retention, and saturated hydraulic conductivity of a soil 20 years after establishing tillage and straw management treatments in interior Alaska. The strip plot experimental design, established on a silt loam and maintained in continuous barley (Hordeum vulgare L.), included tillage as the main treatment and straw management as the secondary treatment. Tillage treatments included no tillage, autumn chisel plow, spring disk, and intensive tillage (autumn and spring disk) while straw treatments included retaining or removing stubble and loose straw from the soil surface after harvest. Soil properties were measured after sowing in spring 2004; saturated hydraulic conductivity was measured by the falling-head method, infiltration was measured using a double-ring infiltrometer, and water retention was assessed by measuring the temporal variation in in-situ soil water content. No tillage resulted in greater saturated hydraulic conductivity and generally retained more water against gravitational and matric forces than other tillage treatments. Infiltration was greater in autumn chisel plow than other tillage treatments and was presumably suppressed in no tillage by an organic layer overlying mineral soil. Infiltration was also enhanced by retaining straw on rather than removing straw from the soil surface after harvest. No tillage is not yet a sustainable management practice in this region due to lack of weed control strategies. In addition, the formation of an organic layer in no tillage has important ramifications for the soil hydrological and thermal environment. Therefore, minimum tillage (i.e., autumn chisel plow or spring disk) appears to be a viable management option for maximizing infiltration in interior Alaska.     

Twenty years of tillage research in subarctic Alaska: I. Impact on soil strength,aggregation, roughness,and residue cover

Soil properties and surface characteristics affecting wind erosion can be manipulated through tillage and crop residue management. Little information exists, however, that describes the impact of long term tillage and residue management on soil properties in the subarctic region of the United States. This study examines the impact of 20 years of tillage and residue management on a broad range of physical properties that govern wind erosion processes on a silt loam in interior Alaska. A strip plot experimental design was established in 1983 and included intensive tillage (autumn and spring disk), spring disk, autumn chisel plow, and no tillage with straw either retained on or removed from the soil surface. Soil and residue properties measured after sowing barley (Hordeum vulgare L.) in May 2004 included penetration resistance, soil water content, shear stress, bulk density, random roughness, aggregate size distribution, and residue cover and biomass. No tillage was characterized by larger aggregates, greater soil strength (penetration resistance and shear stress), wetter soil, and greater residue cover compared to all other tillage treatments. Despite crop failures the previous 2 years, crop residue management influenced residue biomass and cover, but not soil properties. Autumn chisel and spring disk appeared to be viable minimum tillage options to intensive tillage in controlling erosion. Autumn chisel and spring disk promoted greater roughness, aggregation, and residue cover as compared with intensive tillage. Although no tillage appeared to be the most effective management strategy for mitigating wind erosion, no tillage was not a sustainable practice due to lack of weed control. No tillage also resulted in the formation of an organic layer on the soil surface over the past 20 years, which has important ramifications for long term crop production in the subarctic where the mean annual temperature is <0 °C.     

Twenty years of tillage research in subarctic Alaska: I. Impact on soil strength, aggregation, roughness, and residue cover

Soil properties and surface characteristics affecting wind erosion can be manipulated through tillage and crop residue management. Little information exists, however, that describes the impact of long term tillage and residue management on soil properties in the subarctic region of the United States. This study examines the impact of 20 years of tillage and residue management on a broad range of physical properties that govern wind erosion processes on a silt loam in interior Alaska. A strip plot experimental design was established in 1983 and included intensive tillage (autumn and spring disk), spring disk, autumn chisel plow, and no tillage with straw either retained on or removed from the soil surface. Soil and residue properties measured after sowing barley (Hordeum vulgare L.) in May 2004 included penetration resistance, soil water content, shear stress, bulk density, random roughness, aggregate size distribution, and residue cover and biomass. No tillage was characterized by larger aggregates, greater soil strength (penetration resistance and shear stress), wetter soil, and greater residue cover compared to all other tillage treatments. Despite crop failures the previous 2 years, crop residue management influenced residue biomass and cover, but not soil properties. Autumn chisel and spring disk appeared to be viable minimum tillage options to intensive tillage in controlling erosion. Autumn chisel and spring disk promoted greater roughness, aggregation, and residue cover as compared with intensive tillage. Although no tillage appeared to be the most effective management strategy for mitigating wind erosion, no tillage was not a sustainable practice due to lack of weed control. No tillage also resulted in the formation of an organic layer on the soil surface over the past 20 years, which has important ramifications for long term crop production in the subarctic where the mean annual temperature is <0 °C.     

Effects of conservation tillage on hydraulic properties of a Griswold silt loam soil

The effects of conservation tillage (CT) systems on crop production and erosion control have been well documented, but limited information is available concerning the effects of different CT systems on the hydraulic properties of layered soils. The effects of three CT treatments: chisel (CH), no-tillage (NT) and till-plant (TP) as compared with conventional modlboard plowing (CN) were investigated on a Griswold silt loam soil (Typic Argiudoll), formed in loess overlaying glacial till. Hydraulic properties were determined in situ. In addition, hydraulic conductivity was determined in the laboratory where more detailed hydraulic conductivity changes were monitored for the lower soil moisture tension range near soil saturation.

At or near saturation, there was no difference in hydraulic properties for all four tillage treatments. For example, mean saturated hydraulic conductivities (from laboratory determination) were 25.5, 25.1, 24.2 and 22.8 cm day⁻¹ for CN, CH, TP and NT, respectively. However under unsaturated conditions, tillage treatments and soil layering (discontinuity between surface loess and glacial till beneath) affected hydraulic properties. In situ hydraulic conductivity (K) ranked CH>CN = NT = TP for the 0.32–0.33 m³ m⁻³ moisture content range. There were no differences in K for all treatments at other moisture ranges considered and at moisture contents 0.31 m³ m⁻³, in situ specific moisture capacity was, however, significantly lower in NT than in the other three treatments. Throughout the 20-day free drainage period for in situ K determination, the effect of layering is exhibited by the mean K values at the 50-cm depth being higher than those at 25 cm. There were negligible treatment-block interaction effects on the hydraulic properties as the soil became drier. Spatial variability in hydraulic properties was also noted for all treatments and soil depths considered.     

保护性耕作对土壤风蚀的影响

保护性耕作能够有效减少农田土壤风蚀.通过室内风洞模拟试验,研究秸秆覆盖、留茬和垄作3种保护性耕作措施对黄土高原北部农田土壤风蚀的影响.结果表明:1)秸秆覆盖和留茬能有效降低土壤风蚀速率,秸秆覆盖量为4 210 kg/hm2时土壤风蚀速率最小,与对照相比减少62.8%;垄作在低风速下能够降低土壤风蚀率,垄向与风向垂直时降...     

保护性耕作对土壤物理特性及玉米产量的影响

保护性耕作措施是干旱区农田提高作物产量的新型耕作技术。为了探讨其区域适应性,在2004～2007年期间,以毛乌素沙地南缘的靖边县北部风沙区农田为研究对象,选用了免耕、秸秆覆盖、覆膜和传统翻耕(CK)4种措施,采用完全随机试验设计进行了田间定位试验研究。结果表明,秸秆覆盖和免耕地的地温在春播初期略比传统翻耕低0.1℃,但随后迅速回升,覆膜在玉米生长期都高于其他措施。耕作措施对播种前土壤容重没有显著影响,而对收获后土壤容重影响显著,与传统翻耕相比,免耕降低了表层土壤容重1.65%,但次层20～40 cm容重增加了1.8%。3种保护性耕作措施均增加了土壤含水量,顺序依次为秸秆覆盖>覆膜>免耕>翻耕,且在作物需水关键期免耕和秸秆覆盖下的土壤含水量相对稳定,保证作物需水,提高水分利用率,分别为8%、22.0%和13.3%。使作物分别增产4.44%、13.14%和19.26%。因此,保护性耕作在风沙区有利于改善农田土壤物理条件,提高作物产量,适于在风沙区推广。     

小麦玉米秸秆掺土还田量对土壤水分运动特性的影响

为探求小麦、玉米秸秆还田对土壤水分运动特性的影响,利用非饱和导水率测定仪测定土壤水分特征曲线,采用van-Genuchten模型拟合土壤水分特征曲线。试验以不掺加任何秸秆为对照,另设计分别掺加小麦或玉米秸秆的4个处理,掺加量分别为干土质量的1.0%、1.6%、2.25%、3.2%,比较各处理土壤水分运动参数和水分有效性差异。结果表明,掺加秸秆后模型进气值倒数值均小于对照;在秸秆掺加量为1%~2.25%时,形状系数值随着秸秆掺加量的增大而增大,当掺加量为3.2%时反而减小;秸秆的掺入还影响到土壤水分特征曲线的土壤残余含水率和土壤饱和含水率,掺加2种秸秆后,土壤饱和含水率均比未掺时小;土壤残余含水率变化规律与形状系数值一致,掺加小麦秸秆后,土壤残余含水率略低于对照,而掺加玉米秸秆后,土壤残余含水率略高于对照。掺加秸秆能减少土壤重力水19.3%~73.3%,在掺加小麦秸秆3.2%、掺加玉米秸秆2.25%时,土壤中易利用水比例系数最大,分别为26.3%、30.6%,所以通过掺加秸秆能显著提高土壤的保水性。研究可为阐明秸秆还田后土壤水分运动规律提供理论依据。     

Effect of long-term conservation tillage on soil biochemical properties in Mediterranean Spanish areas

In semi-arid Mediterranean areas, studies of the performance of conservation tillage systems have largely demonstrated advantages in crop yield, soil water storage and soil protection against wind and water erosion. However, little attention has been given to interactions between soil biochemical properties under different tillage practices. Biochemical properties are useful tools to assess changes caused by different soil tillage systems in long-term field experiments. This study deals with the effect of long-term tillage practices (reduced tillage and no-tillage vs. traditional tillage) on soil chemical properties and microbial functions in three different sites of Spain (two of them located in the Northeast and one in the Southwest) under semi-arid Mediterranean conditions. Soil biological status, as index of soil quality, was evaluated by measuring microbial biomass carbon (MBC) and dehydrogenase (an oxidoreductase) and protease (a hydrolase) activities at three soil depths (0–5, 5–10 and 10–25 cm). In the three experimental areas, increases in soil organic matter content, MBC and enzymatic activities were found at the superficial layers of soil under conservation tillage (reduced tillage and no-tillage) in comparison with traditional tillage. Values of the stratification ratio of some biochemical properties were significantly correlated with yield production in Northeast sites.Conservation tillage has proven to be an effective strategy to improve soil quality and fertility in Mediterranean areas of Spain.     

Dynamics of soil hydraulic properties during fallow as affected by tillage

There is limited information on the effects of tillage practices on soil hydraulic properties, especially changes with time. The objective of this study was to evaluate on a long-term field experiment the influence of conventional tillage (CT), reduced tillage (RT) and no-tillage (NT) on the dynamics of soil hydraulic properties over 3 consecutive 16–18 month fallow periods. Surface measurements of soil dry bulk density (ρ_b), soil hydraulic conductivity (K(ψ)) at −14, −4, −1 and 0 cm pressure heads using a tension disc infiltrometer, and derived hydraulic parameters (pore size, number of pores per unit of area and water-transmission porosity) calculated using the Poiseuille's Law were taken on four different dates over the fallow period, namely, before and immediately after primary tillage, after post-tillage rains and at the end of fallow. Under consolidated structured soil conditions, NT plots presented the most compacted topsoil layer when compared with CT and RT. Soil hydraulic conductivity under NT was, for the entire range of pressure head applied, significantly lower (P < 0.05) than that measured for CT and RT. However, NT showed the largest mean macropore size (0.99, 0.95 and 2.08 mm for CT, RT and NT, respectively; P < 0.05) but the significantly lowest number of water-conducting pores per unit area (74.1, 118.5 and 1.4 macropores per m² for CT, RT and NT, respectively; P < 0.05). Overall, water flow was mainly regulated by macropores even though they represented a small fraction of total soil porosity. No significant differences in hydraulic properties were found between CT and RT. In the short term, tillage operations significantly increased K (P < 0.05) for the entire range of pressure head applied, which was likely a result of an increase in water-conducting mesopores despite a decrease in estimated mesopore diameter. Soil reconsolidation following post-tillage rains reduced K at a rate that increased with the intensity of the rainfall events.     

Relationship between soil structure and runoff/soil loss after 24 years of conservation tillage

A better understanding of tillage and stubble management effects on surface soil structure is vital for the development of effective soil conservation practices for the long-term. Relationships between aspects of soil structure and runoff/soil loss were investigated in 24 year old field experiment on an Oxic Paleustalf, in NSW, Australia. Two tillage/stubble management systems were compared, namely direct drilled/stubble retained (DD/SR) versus conventional tillage/stubble burnt (CC/SB). Tillage and stubble burning significantly increased bulk density and decreased the macro-aggregate stability, mean weight diameter (MWD), geometric mean diameter (GMD) and total porosity, particularly macroporosity (>60 μm). For the 0–5 cm layer, DD/SR had significantly higher water stability of macro-aggregates >2 mm than CC/SB (165 g/kg versus 78 g/kg), and the volume of pore space of diameter >60 μm at 0–5 cm depth was significantly greater (more than 11%) for DD/SR than for CC/SB. Under simulated rainfall (100 mm/h) and the removal of surface stubble, both runoff and soil loss were significantly higher under CC/SB compared to DD/SR. The infiltration rate at the end of the experiment under DD/SR was 3.7 times that of CC/SB (85 mm/h versus 23 mm/h). There were significant correlations between the proportion of soil particles >0.25 mm measured after wetting by rain and both final infiltration rate (P < 0.001) and soil loss (P < 0.001). It was concluded that 24 years of direct drilling and stubble retained practices significantly reduced runoff and soil erosion hazards, due to a fundamental change in soil structure, viz. higher soil aggregate stability and higher macroporosity of the surface soil.     

长期保护性耕作提高土壤大团聚体含量及团聚体有机碳的作用

【目的】团聚体形成被认为是土壤固碳的最重要机制。本文以河南豫西地区长期耕作试验为研究对象,研究了长期保护性耕作对土壤团聚体性质及土壤有机碳(SOC)含量的影响,为探讨土壤固碳机理,优化黄土高原坡耕地区农田耕作管理措施,实现土壤固碳减排、培肥土壤提供理论依据。【方法】长期耕作试验开始于1999年,试验处理有免耕覆盖(NT)、深松覆盖(SM)和翻耕(CT)。利用湿筛法筛分第3年(2002年)和第13年(2011年)0—10cm和10—20 cm土层中,2000、250~2000、53~250和53μm级别的水稳性团聚体,计算团聚体平均质量直径(MWD),并测定了各级别团聚体的有机碳(SOC)含量。【结果】1)连续13年免耕覆盖和深松覆盖显著提高了土壤表层0—10 cm的SOC含量,分别比翻耕增加了33.47%和44.48%。2011年免耕覆盖和深松覆盖SOC含量较2002年上升了1.92%和8.59%,翻耕下降了18.97%。2)与翻耕相比,免耕覆盖和深松覆盖2000μm团聚体含量显著提高了40.71%和106.75%;53~250μm团聚体含量显著降低了19.72%和22.53%;团聚体平均质量直径显著提高了20.55%和39.68%,显示了土壤结构的明显改善。3)免耕覆盖和深松覆盖显著提高了表层土壤所有团聚体有机碳的含量,尤其以2000μm团聚体提升最多。与翻耕相比,2000μm团聚体有机碳分别提高了40.0%和27.6%。4)免耕覆盖和深松覆盖下表层土壤大团聚体有机碳含量随耕作年限增加,微团聚体有机碳随耕作年限降低。2000μm的土壤团聚体有机碳含量2011年较2002年分别升高了23.93%和7.12%,53~250μm微团聚体有机碳含量分别下降了19.58%和13.27%。【结论】长期保护性耕作(包括免耕覆盖和深松覆盖)可显著提高表层土壤大团聚体含量,降低微团聚体含量,提高团聚体的水稳性,改善土壤结构。同时可增加土壤团聚体有机碳含量,提高土壤肥力。长期保护性耕作在河南豫西丘陵地区是一种较为合理的耕作方式。     

Direction-dependent behaviour of hydraulic and mechanical properties in structured soils under conventional and conservation tillage

The development of soil structure units with defined forms and dimensions (e.g. platy by soil compaction or prismatic up to subangular-blocky by swelling–shrinkage processes) can lead to direction-dependent behaviour of mechanical and hydraulic properties. However, little research has investigated direction-dependent behaviour directly. Undisturbed samples were collected at different horizons and orientations (vertical and horizontal) of Stagnic Luvisols derived from glacial till (Weichselian moraine region in Northern Germany). A direct shear test determined the cohesion (c) and the angle of internal friction (φ). The water retention curve (WRC), the saturated hydraulic conductivity (k_s) and the air permeability (k_a) were also measured. The air-filled porosity (_a) was determined and pore continuity indices (N) and blocked porosities (_b) were derived from the relationship between k_a and _a.Although the pore volume as a scalar is isotrop, the saturated hydraulic conductivity and air permeability can be anisotropic. In the seedbed (SB) and plough pan (PP) of conventionally managed soils the effective porosity is non-direction-dependent, however, differences in k_s as a function of sampling direction can reach one order of magnitude in PP (k_sh > k_sv). The shear strength parameters do not present a significant anisotropy, although, a pronounced spatial orientation of soil aggregates (e.g. induced by soil compaction in a plough pan) lead to direction-dependent shear strength (by σ_n: 10 kPa, σ_tv: 12 kPa and σ_th: 19 kPa). This behaviour was especially observed in pore continuity indices (e.g. vertical and horizontal oriented aggregates observed in Bvg and PP presented _bv < _bh and _bv > _bh, respectively) showing that the identification of soil structure can be used as the first parameter to estimate if hydraulic properties present a direction-dependent behaviour at the scale of the soil horizon, which is relevant in modelling transport processes.     

Changes in some soil properties in a Vertic Argiudoll under short-term conservation tillage

The purpose of this work was to determine whether some soil physical and chemical properties, and microbial activity were affected by two conservation tillage systems in a Chernozemic clay loam soil (Vertic Argiudoll), after 5 years of trial initiation. Two crop sequences, corn (Zea mays L.)–wheat (Triticum aestivum L.)/soybean (Glycine max (L.) Merr.) and wheat/soybean, under chisel plowing (ChP) and no till (NT) were evaluated. Physical and chemical properties were also analyzed taking the same soil without disturbance as reference. The Hénin instability index (HI) was larger in ChP than in NT in both corn–wheat/soybean (C–W/S) and wheat/soybean (W/S) sequences (P≤0.05). The C–W/S sequence differed from W/S (P≤0.01) in total organic carbon (TOC). As regards organic carbon fractions, no differences were found in labile organic carbon (LOC), while W/S under ChP showed the lowest value (P≤0.01) of humified organic carbon (HOC). No differences were found in microbial respiration either in crop sequences or in tillage systems. Soil physical and chemical properties differentiated crop sequences and tillage treatments from the undisturbed soil when a Student’s t-test was performed. Five years elapsed since the beginning of this trial was time enough to detect changes in some of the soil properties as a consequence of management practices. An important reduction in the soil structural stability was observed as related to the undisturbed soil. However, the C–W/S sequence under NT resulted in lower soil degradation with respect to the other treatments.     

Grain yields and soil properties on loam soil after three decades with conservation tillage in southeast Norway

Four tillage trials have been performed on moderately well-drained loam soil in southeast Norway for 30–37 years (mean 34), comparing reduced tillage (8–10 cm in spring) with autumn ploughing (25 cm). In some years, additional stubble harrowing in autumn (10–12 cm) was compared with harrowing only in spring. Weeds were controlled with herbicides. Straw residues were retained after around 1990 and no fungicides were used. Grain yields are reported for the last nine years, and compared with earlier years. Results are presented for a number of soil properties measured in recent years. Autumn harrowing gave no consistent yield benefit over harrowing only in spring. There was little difference between ploughed and unploughed treatments in mean grain yields over the whole trial period, and the variability between years was similar in both tillage systems. Relative grain yields, calculated as yields obtained without ploughing in percentage of those obtained with ploughing, appeared to be normally distributed around 100%. Responses were often positive in dry years, and negative in wet years. Reduced tillage gave higher P and K concentrations near the soil surface and slightly lower concentrations in deeper layers. There was little change in their levels, relative to earlier findings. Changes in bulk density and total porosity were mostly attributable to changes in the stratification of organic matter. Reduced tillage increased porosity at 4–8 cm depth and decreased it slightly at 24–28 cm, but there was no change in the intermediate layer. The moisture-holding capacity of the soil was altered little by reduced tillage, and soil aeration properties were satisfactory at all three depths measured. There was no change in the total amount of organic matter stored within the topsoil, despite marked changes in its distribution. Reduced tillage gave significant increases in aggregate stability and an indication of greater earthworm activity.     

A conservation tillage research update from the Coastal plain soil and water conservation research center of South Carolina: A review of previous research

In the U.S. Southeastern Coastal Plains conservation tillage (CT) became useful as a management system with the development of in-row subsoiling systems capable of planting into heavy residues. Research priorities associated with the development of CT included: reducing cover crop water loss, improving stand establishment, assessing nutrient and water management requirements, determining optimal subsoiling strategies, understanding long-term conservation tillage effects on soil properties, evaluating the interaction of crop residue removal with tillage systems, and documenting tillage impact on pests and beneficial organisms. Since the late 1970s the Coastal Plains Soil and Water Conservation Research Center in Florence, SC has made a concerted effort to study these interactions and alleviate them as obstructions to the use of CT management. These studies showed that for Coastal Plain soils such as Norfolk sandy loam (fine-loamy, siliceous thermic, Typic Paleudults) winter cover crops such as rye (Secale cereale L.) desiccated the soil profile by evapotranspiration in the spring. This delayed emergence and early season growth of corn (Zea mays L.) but not full-season soybean (Glycine max (L.) Merr.). Conservation tillage helped manage soil strength by gradually increasing soil organic matter content, restricting traffic patterns and maintaining higher soil water contents. Laboratory studies demonstrated a negative correlation (R²=0.85) between proctor soil strength and organic matter content. Conservation tillage affected nematode, Bradyrhizobium japonicum and Heliothis species populations. Alternate cropping systems using rapeseed (Brassica napus L.) as a winter crop or sunflower (Helianthus annuus L.) either before soybean or after corn provided crop cover against potential soil loss from late autumn through early spring, when bare soil is exposed to intense rainfall. Water quality questions associated with CT have been raised but remain unanswered. Although CT can reduce runoff and erosion, the crop residues can support higher insect populations and pathogen inoculum levels, and thus prompt greater pesticide use. Quantifying relationships between soil strength, macropore formation and persistence, and water infiltration with surface and subsurface water quality is the focus of new long-term evaluations. The findings of these studies, published to date, are summarized in this paper.     

Changes in soil properties and soil solution nutrients due to conservation versus conventional tillage in Vertisols

Understanding of tillage effects on soil chemical properties and cations in soil solution dynamics is essential for making appropriate land-management decisions. Measurements were made after more than 25 years of different tillage treatments: conventional tillage (CT) and conservation tillage, which includes no-till (NT) and minimum tillage (MT). pH and bulk density did not show important changes but exchangeable cations and cations in soil solution were affected by depth and different tillage. The highest concentration of exchangeable Ca²⁺ and Mg²⁺ was found in NT, decreased in MT and the lowest concentration was found in CT (mean values were 26.0, 24.4 and 23.3 cmol_c kg^?1 for exchangeable Ca²⁺ and 4.2, 3.7 and 3.3 cmol_c kg^?1 for exchangeable Mg²⁺ in NT, MT and CT, respectively). In addition, the highest concentration of exchangeable Na⁺ was found in NT, decreased in CT and the lowest concentration was found in MT. However, the highest concentration of exchangeable K⁺ was found in MT. A significant depth effect was observed for cations in soil solution: Na⁺ increased with depth whereas K⁺ and Ca²⁺ decreased with depth. This study aims to demonstrate the effect of tillage on the distribution and concentration of certain chemical soil properties.     

少免耕土壤结构与导水能力的季节变化及其水保效果

通过对黑土坡耕地免耕、少耕与传统耕作土壤物理性状全生育期观测,比较研究土壤结构和导水性状季节变化差异及其与水土流失的关系。结果表明,表层0~20 cm土壤,免耕土壤容重全生育期维持在1.20~1.30 g cm-3,变化小,大于0.25 mm的水稳性团聚体含量(WR0.25)和平均重量直径(MWD)高于传统耕作,初始和稳定入渗速率均高于少耕和传统耕作,土壤含水量分别较少耕和传统耕作高4.7和4.4个百分点,较传统耕作分别减少地表径流和土壤流失量86%和100%;少耕除夏季各项性状均介于免耕和传统耕作之间,夏季垄沟深松后,垄沟土壤容重显著降低,较免耕和传统耕作降低0.15 g cm-3以上,提高土壤初始入渗速率30%以上,较传统耕作减少水和土壤流失量20%和40%。传统耕作土壤容重,垄台由播种时的0.91 g cm-3增加至收获时的1.23 g cm-3,垄沟一直维持在1.30 g cm-3左右,WR0.25、MWD、土壤稳定入渗速率、含水量均较低,全生育期10%的雨水流失,土壤流失量615 t km-2a-1。免耕土壤结构稳定,蓄水保水最佳,为效果显著的水土保持耕作措施,少耕也有一定的保水保土作用;免耕和少耕均能够改善土壤物理性状。     

保护性耕作对土壤水分和小麦产量的影响

采用3种稻田保护性耕作栽培模式与传统栽培模式的定位试验,对成都平原稻田小麦季的土壤水分及产量进行了研究。结果表明:小麦全生育期,免耕覆盖处理的土壤含水率明显地高于翻耕覆盖处理,而翻耕不覆盖处理最差;小麦分蘖高峰期,覆盖处理的土壤含水率比不覆盖处理高17.7%～75.9%,免耕覆盖处理的土壤含水率比翻耕覆盖处理高12.7%～41.0%;免耕覆盖处理的小麦最高茎蘖数又比翻耕覆盖处理增加23.8%～72.3%,均极显著优于翻耕处理;覆盖处理的小麦产量比不覆盖处理增产6.3%～19.5%,免耕覆盖处理比翻耕覆盖处理增产3.2%～8.0%。稻田保护性耕作有利于提高成都平原区小麦产量。     

Influence of long-term conservation tillage on soil and rhizosphere microorganisms

 In long-term field experiments on sandy loam and loamy sand soils, the influence of conservation and conventional tillage on soil and rhizosphere microorganisms was studied. Conservation tillage stimulated rhizosphere bacteria on winter wheat, winter barley, winter rye and maize in different soil layers. Particularly the populations of Agrobacterium spp. and Pseudomonas spp. were increased. On the sandy loam, N₂ fixation and nodulation of pea plants were significantly increased. No influence of different soil tillage was determined on the colonization of the rhizosphere by mycorrhiza and saprophytic fungi. Stubble residues infected with Gaeumanomyces graminis were infectious for a longer time on the soil surface than after incorporation into the soil. Received: 10 March 1998