青海省东部山区旱作农田土壤团聚体特征研究

比较了青海省东部山区垂直梯度分布的三种旱作农田土壤(黑钙土、栗钙土、灰钙土),在0~60 cm土层的不同粒级土壤风干团聚体和水稳性团聚体含量间的差异,并结合其它土壤质量指标(有机质、粘粒)对不同土壤结构和抗侵蚀能力进行了综合评价。结果表明,>0.25mm风干团聚体、>0.25mm水稳性团聚体含量和土壤有机质含量与土壤类型间有密切关系。均表现为黑钙土>栗钙土>灰钙土。黑钙土和栗钙土的土壤有机质含量与>0.25mm水稳性团聚体间存在显著正相关关系(P<0.05),灰钙土则无明显相关性;三种土壤粘粒含量与>0.25mm风干团聚体和0.25mm水稳性团聚体含量间无明显相关性。各项指标综合比较,三种土壤抗侵蚀能力大小为:黑钙土>栗钙土>灰钙土。     

中国古代土壤耕作理论和技术的历史演进

“耕为农事之首”,“欲求足食之道,先明力耕之法”。我国古代就高度重视土壤耕作在农业增产中的重要作用,先民们在长期的农业生产实践中,积累了丰富的土壤耕作的经验,并把直观经验上升为土壤耕作理论和技术,本文以历史时代为线索,对我国古代土壤耕作理论和技术的产生和发展及其基本内容进行一些分析和探讨,以期对当今土壤耕作科学具有借鉴意义。     

影响土壤磷有效性变化作用机理

土壤磷有效性对植物生长以及磷的生态系统生物循环过程具有重要意义,一直以来也是国内外磷素研究的重点之一,文章综合介绍了土壤环境中影响磷有效性的一些因子及其作用机理,以期为系统的认识土壤中磷的有效性的变化提供借鉴。     

淮北变性土性状特点对其生产性能的影响及农业利用对策

本研究基于黄淮海平原多个变性土剖面分层土壤样品的土壤理化性状分析数据,对其肥力特征、生产性能以及培肥改良措施进行了系统研究。相关结果表明,机械组成中粘粒含量高、质地粘重、土壤结构和孔隙性差是变性土主要物理性状特征,受其影响,土壤表现出耕作性能差、蓄水能力弱、保水性能不强等特点;化学性状主要表现为有机质含量不高、质量差,土壤氮素水平仍较低,耕层土壤速效磷含量分异加大,土壤速效钾含量缓慢降低,土壤CEC含量较高,土壤保肥性能强,但供肥性能较差等特点。这些性状特点对土壤生产性能的影响主要表现在土壤适耕期短,易受旱、涝(渍)灾害的危害,土壤有效养分低、营养失调,钙质结核影响土壤蓄水能力和水分运行以及作物根系生长等方面。指出:(1)增加土壤有机质,改良土壤理化性质;(2)合理施肥,促进土壤养分平衡;(3)改进耕作、灌溉技术,调控土壤水分状况等是培育变性土肥力质量、提高土壤生产性能的关键性措施。     

贵溪冶炼厂周边农田土壤重金属污染特性及评价

在对贵溪冶炼厂周边区域的农田土壤及生产的稻谷进行采样调查和数据处理分析的基础上,对农田土壤重金属污染特性和现状进行了监测和初步评价,结果表明:农田土壤重金属污染可能来源于贵溪冶炼厂废水的排放及尾矿渣的堆放,与灌溉水源无关;用国家土壤环境质量二级标准进行评价可知,农田土壤重金属的综合污染指数较高,土壤污染已处于重度污染等级,单项重金属污染指数表明Cu、Cd的含量已严重超标,并处于重度污染等级,Zn、Pb和As的含量未构成污染;水泉村、竹山村与所生产的稻谷三者之间呈显著或极显著正相关,即农田生态系统呈复合污染的趋势。     

Influence of management practices on soil organic matter changes in the Northern China plain and Northeastern China

Soil organic matter (SOM) is strongly related to soil type and management practices. Changes in government policy have brought drastic changes in farm management practices in the last two decades in rural China. This study investigates changes in SOM in two different soils: Ustepts and Udolls. Ustepts, in the North China Plain where the climate is warm and sub-humid, developed from an alluvial flood plain with organic matter <10 g kg⁻¹. Udolls, in Northeastern China where the climate is cool and sub-humid, developed from loess-like materials with organic matter >20 g kg⁻¹. Two locations for Ustepts and three locations for Udolls were used to collect 567 soil samples in 1980–1982 and again in 2000 for SOM analysis. Soil organic matter increased for Ustepts and decreased for Udolls soils over the sampling period, resulting from differences in fertilizer rates and crop residue input to soil. Higher fertilizer input and crop intensity and initially very low SOM content in Ustepts all contributed to greater OM input than oxidation release. In contrast, lower fertilizer input and crop intensity, and initially high SOM content in the Udolls, led to lower OM input than oxidation release. Increasing SOM content through higher mineral fertilizer input is a valuable option for sustainable agriculture production in areas where SOM is low and there is a shortage or potential shortage of food supply.     

Effects of rake angle of chisel plough on soil cutting factors and power requirements: A computer simulation

A computer simulation was conducted to predict the effects of rake angle of a chisel plough and soil bulk density on angle of soil failure plane, rupture distance, width of side crescent, frictional, overburden, cohesion and adhesion soil cutting factors, draft forces and drawbar power requirements. The experimental work was carried out in two locations. Soil of the first location was sandy clay with the soil bulk densities of 1.75 and 1.70 g/cm³ for firm and loose soil conditions, respectively, with an angle of internal friction of 30° and a surface friction angle of 20°, cohesion of 2.5 kN/m² and adhesion of 1.2 kN/m². Soil of the second location was clay loam with the soil bulk densities of 1.65 and 1.50 g/cm³ for firm and loose soil conditions, respectively, with an angle of internal friction of 34° and a surface friction angle of 23°, cohesion of 2.4 kN/m² and adhesion of 1.14 kN/m². The prediction showed that the angle of failure plane found to decrease with the rake angle. The rupture distance decreased with the rake angle from 15° to 55° and then increased as the rake angle increased over 55°. The width of the side crescent increased as the rake angle increased and the maximum value and the minimum value were recorded at 75° and at 15°. Values of frictional and overburden factors decreased as rake angle increased. The maximum and minimum values were recorded at 15° and 75°, respectively. The values of cohesion factor increased as rake angle increased. The maximum value was recorded at rake angle of 75° and the minimum value was recorded at rake angle of 15°. Adhesion factor was found to change inversely with the rake angle from 15° to 55° and then to change directly with the rake angle over 55°. The draft force decreased with the rake angle and reached its minimum value at 45° rake angle. Over 45°, the draft force increased and reached its maximum value at 75° rake angle. The draft increased with soil bulk density. The power required for moving the plough recorded the maximum value at rake angle of 15°, while the minimum value was recorded at 55° rake angle. The values of power increased with decrease of soil bulk density. The predicted values demonstrated some deviations from the experimental values of the draft force and the drawbar power.     

Microbial activity affected by lime in a long-term no-till soil

Under conventional farming practices, lime is usually applied on the soil surface and then incorporated into the soil to correct soil acidity. In no-till (NT) systems, where lime is surface applied or only incorporated into the soil to very shallow depth, lime will likely not move to where it is required within reasonable time. Consequently, lime may have to be incorporated into the soil by mechanical means. The objective of this laboratory study was to characterize the effect of lime, incorporated to different depths, on chemical and biological soil properties in a long-term NT soil. Soil samples taken from the 0–5, 0–10, and 0–20 cm depths were analyzed in incubation studies for soil pH, nitrate, CO₂ respiration, and microbial biomass-C (MBC). Lime (CaCO₃) was applied at rates equivalent to 0, 4.4, 8.8, and 17.6 Mg ha⁻¹. Application of lime to both 0–10 and 0–20 cm depths increased soil pH from about 4.9 by 1, 1.7, and 2.8 units for the low, medium, and high liming rates, respectively. Soil nitrate increased over time and in proportion to liming rate, suggesting that conditions were favorable for N-mineralization and nitrification. Greater respiration rates and greater MBC found in lime-treated than in non-limed soils were attributed to higher soil pH. Faster turnover rates and increased mineralization of organic matter were found in lime-treated than in non-limed soils. These studies show that below-surface lime placement is effective for correcting soil acidity under NT and that microbial activity and nitrification can be enhanced.     

Stress wavelets: Multi-scale and multi-resolution assessment of soil structure by the drop-shatter method

Stress wavelet properties are inherently involved in the process of the drop-shatter method of assessment on soil structural characteristics. The analogies between wavelet analysis and the drop-shatter process are based on two factors: scale and resolution. By carefully following the requirements of wavelet analysis, a standard procedure of soil fragmentation and sieving is described. Following this procedure, a set of equations can be derived from which surface contacting energy between soil aggregates of a specific scale can be calculated. The resultant values in fact mirror the multi-resolutions of wavelets.

Natural soil clods as well as artificial structured soil cores were used for fragmentation. Though the experiment can do well on natural soil clods, and it is precise enough in predicting structural state of a sub-dimensional clods of 8 mm, its use on artificial soil cores produced a set of data that was quite chaotic. The unique behavior experienced in the process of fragmentation of artificial soil structure indicates that there is no distinct stage between mother soil clods (cores) and its constituent primary particles. Such a state should result from an excessively large impact energy (too low a resolution in the wavelet analysis) for each drop stroke impact.

With an ultimate goal for soil process simulation, the construction of the experiment for artificial structured soil core preparation brings the traditional methods of sample preparation a step forward further by creating an environment much nearer to the field conditions experienced in natural soils. Still, extensive refinements are needed, especially for the mode of water application, cycle and intensity of management.     

Effect of tillage and mode of straw mulch application on soil erosion in the submontaneous tract of Punjab, India

The submontaneous tract of Punjab comprising 10% of the state, is prone to soil erosion by water. Soils of the area are coarse in texture, low in organic matter and poor in fertility. High intensity rains during the monsoon season result in fertile topsoil removal. There is an urgent need to control soil erosion in this region so as to improve soil productivity. A field study was conducted to estimate the effect of tillage and different modes of mulch application on soil erosion losses. Treatments comprised two levels of tillage, viz. minimum (T_m) and conventional (T_c) in the main plots and five modes of straw mulch application, viz. mulch spread over whole plot (M_w), mulch spread on lower one-third of plot (M_1/3), mulch applied in strips (M_s), vertical mulching (M_v) and unmulched control (M_o), in subplots in a replicated split plot design. Rate of mulch application was 6 t ha⁻¹ in all modes. Compared with M_o, M_w reduced runoff by 33%. Runoff and soil loss were 5 and 40% higher under T_c than under T_m. Though other modes of straw mulch application (M_1/3, M_s and M_v) controlled soil loss better than M_o, their effectiveness was less than M_w. T_m was more effective in conserving soil moisture than T_c. Compared with M_o, M_w had 3–7% higher soil moisture content in the 0–30 cm soil depth under T_m. Minimum soil temperature of the surface layer was 1.4–2.4 °C lower under M_w than under M_o. Straw mulching reduced maximum soil temperature and helped in conserving soil moisture. Minimum tillage coupled with M_w was highly effective in reducing soil erosion losses, decreasing soil temperature and increasing moisture content by providing maximum surface cover.