The role of clay, organic carbon and long-term management on mouldboard plough draught measured on the Broadbalk wheat experiment at Rothamsted

Despite a high energy requirement, the mouldboard plough remains the dominant tillage tool in northwest Europe. The aim of this work was to evaluate the relative influences of soil texture (clay content), soil organic carbon (SOC) and long‐term management on soil‐specific draught (S), where S is the force per cross‐sectional area of worked soil. Measurements were made during autumn 2000 on the then 157‐year‐old Broadbalk wheat experiment at Rothamsted, UK, where clay contents vary from 19 to 39% and the different cropping history, mineral and organic fertilizer treatments lead to SOC values of 0.7–3.2%. Minimum SOC values increased with increasing clay and were associated with zero or low mineral N inputs, while higher SOC values (>2%) were associated with long‐term applications of farmyard manure (FYM), despite these being on the lighter (<24% clay) soils. S values ranged between 52 and 142 kPa, with higher values co‐located in areas with high clay contents. Contour maps were generated to illustrate the spatial variability of S and show similarity to those for clay. Where FYM had been added, S was 66 kPa compared with 74 kPa where only mineral or no fertilizer was applied on soils of the same texture. Increasing applications of mineral N resulted in relatively small increases in SOC but up to 12% reduction in S.     

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.     

Optimum versus non-limiting water contents for root growth, biomass accumulation, gas exchange and the rate of development of maize (Zea mays L.)

Many biological processes vary in a curvilinear manner, reaching a maximum rate at an optimum water content. Optimum conditions commonly extend across a range in water contents, and providing there are no soil-related limitations to biological processes, this range can be referred to as the non-limiting water range (NLWR) of a soil. The rate of a biological process would be expected to be similar in soils with different structure when the water content is in the NLWR and soils are under similar environmental conditions. This range potentially is a useful characteristic to describe the quality of soil structures with respect to a biological process—the larger the range the higher the quality. The distinction between optimum and NLWR has received little attention. The objective of this study was to determine if gas exchange rates, biomass accumulation in shoots and roots, root morphology and rate of development of maize (Zea mays L.) vary among soils under optimum soil water contents. Plants were grown to the 12-leaf stage under controlled environment conditions in four soils of different texture, packed to two levels of compaction with two rates of N addition and maintained at three different water contents. The optimum water content, for processes involving both shoots and roots, bracketed an air content of 0.15 for the different soils. The magnitude of the plant responses at optimum water content varied among soils and with relative compaction. Plant responses were largest in the Conestogo (loam soil) and smallest in soils with the highest clay contents. The magnitude of several responses decreased with increasing compaction. In the process of determining the NLWR, it is not appropriate to assume that either shoot or root characteristics are similar in soils of different structure when the water content of each soil is within a range that is optimum for that soil. The largest root and shoot growth that can be achieved at optimum water content across a range of soil conditions must be determined and NLWR determined on soils exhibiting these growth rates. Soils at their optimum water content with root and shoot growth that are less than the largest values imply the existence of soil-related limitations and therefore, by definition, have a value of zero for NLWR.     

生育期水分调控对甘肃河西地区滴灌春小麦氮素吸收和利用的影响

【目的】针对河西地区水资源短缺、作物水肥利用效率低等问题,研究滴灌施肥条件下生育期土壤水分调控对河西地区春小麦氮素吸收和利用的影响,以期探索提高氮肥利用效率的土壤水分调控模式。【方法】以春小麦‘永良 4 号’为试验材料进行田间小区试验,根据前期的滴灌施肥试验,施氮量为 N 180 kg/hm2,在春小麦生育期设置 5 个土壤水分下限 (W1、W2、W3、W4 和 CK) 控制水平,研究生育期土壤水分调控对河西地区滴灌春小麦氮素吸收、分配和转运及根区土壤硝态氮含量的影响。【结果】1) 一定的施肥水平下,土壤水分下限的增长会增加各处理小麦的生育期总灌水量,以充分灌溉 (CK) 处理最大,分别比 W1、W2、W3、W4 处理高 26.6%、15.0%、9.3% 和 4.8%。2) 灌水量的增加会促进小麦植株对土壤养分的吸收同化,与 W4 处理相比,W1、W2、W3 处理的氮素吸收量分别显著减少 29.3%、23.0% 和 15.5%,CK 与 W4 处理差异不显著 (P>0.05)。3) 成熟期各处理小麦营养器官中氮素吸收量以 CK 处理最大,分别比 W1、W2、W3、W4 处理高 28.2%、28.6%、19.2% 和 12.7%,但其子粒中的氮素吸收量比 W4 处理显著低 10.4%。开花期后营养器官中的氮素向子粒的转移量和转移率均以 W4 处理最大,分别比 W1、W2、W3、CK 处理显著增加 40.4%、28.0%、10.6%、10.0% 和 6.8%、3.5%、1.3%、6.9%,但 W4 处理小麦氮素转移量对子粒的贡献率最小 (76.2%)。随着土壤水分下限的增加,各处理氮素吸收效率、氮素生产效率及氮素收获指数呈先增加后减小的变化趋势,均在W4处理下获得最大值。4) 在一定施肥水平下,灌水量的增加会加大硝态氮向土壤深处运移,不利于小麦植株对土壤硝态氮的吸收利用。5) 生育期土壤水分调控对小麦根区土壤硝态氮含量有显著性影响,成熟期 0—100 cm 土层内土壤硝态氮累积量以 W4 处理最小,分别比 W1、W2、W3 和对照 (CK) 处理减少 9.6%、7.2%、6.6% 和 1.4%。【结论】适宜的土壤水分调控更有利于小麦植株对土壤养分的吸收,综合考虑氮素吸收、分配及土壤硝态氮等因素,W4 是基于本试验条件下河西地区滴灌春小麦最佳土壤水分下限处理。