少免耕土壤结构与导水能力的季节变化及其水保效果

SEASONAL VARIATIONS OF SOIL STRUCTURES AND HYDRAULIC CONDUCTIVITIES AND THEIR EFFECTS ON SOIL AND WATER CONSERVATION UNDER NO-TILLAGE AND REDUCED TILLAGE

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^-2 a^-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。

Changes in soil physical properties in the surface layer （0-20 cm） on a sloping farmland of Mollisols under no-tillage （NT）, reduced tillage （RT） and conventional tillage （CT）, separately, were monitored throughout the entire crop growing season for comparison to explore differences between soils under tillage patterns in seasonal variation of soil structure and hydraulic conductivity and relationships of the variations with soil-water loss. Results show that soil bulk density in NT varied slightly, remaining in the range of 1.20-1.30 g cm^-3. NT was higher than CT in content of water stable soil aggregate 〉 0.25 mm size （WR0.25） and mean weight diameter （MWD）, higher than RT and CT in initial and stable soil infiltration rate, 4.68% and 4.44% higher than RT and NT in mean soil water content, and 86% and 100% lower than CT in runoff and soil loss, respectively. RT ranged between NT and CT in all the measured properties, throughout the season except in summer. In RT, deep tillage of the furrows in summer significantly lowered soil bulk density in the furrow, at least 0.15 g cm^-3 lower than that in NT and CT, thus increasing the initial soil infiltration rate by 30% or more. RT was 20% and 40% lower than CT in soil and water loss, respectively. In CT, soil bulk density in ridge increased from 0.91 g cm^-3 at the seeding stage to 1.23 g cm^-3 at the harvesting stage, and that in furrow remained around 1.30 g cm^-3 . CT was lower than the other two in WR0.25, MWD, soil infiltration rate and soil water content. It lost 10% of the rainfall it had during the entire the crop growing season and soil at 615 t km^-2 a^-1. NT was rather stable in soil structure and the best in soil-water conservation among the three. Hence, it is a tillage practice significant in soil-water conserving effect. RT is also a practice that has some soil-water conserving effect. And both of the practices help improve soil physical properties.