Effects of soil erosion and soil amendment on soil aggregate stability in the cultivated-layer of sloping farmland in the Three Gorges Reservoir area

Abstract

Soil aggregate stability is an important parameter that indicates soil resistance to erosion and the potential productivity of sloping farmland. The cultivated-layer (0–20 cm) of typical sloping purple soil (entisol) farmland around the Three Gorges Reservoir was studied. In-situ controls test and shovel test were used to determine the response of water stable aggregates to two factors, degree of erosion and soil amendment (CK, no fertilizer; F, chemical fertilizer; and BF, biochar with chemical fertilizer) and to analyze regulating pathways of the rational cultivation layer for sloping farmland. Water stable aggregate content for each soil particle size fraction in the cultivated-layer was significantly different for all degrees of erosion. The fraction of particle size > 5 mm in subsurface soil (10–20 cm) was greater than in topsoil (0–10 cm). Erosion significantly affected soil aggregate stability (WR0.25, >0.25 mm particle size water-stable aggregates content; MWD, mean weight diameter of aggregates; GMD, geometric mean diameter of aggregates) in the cultivated-layer. Both MWD and GMD reached maximums for S-0 (erosion of 0 cm). Comparing all treatments, it is BF that showed greater weight increase for MWD and GMD in topsoil (0–10 cm). Percentage of aggregate disruption consistently increased along downward direction of erosion degrees. Shear strength and penetration resistance, which are soil macrostructure parameters, were used to quantify soil stability in a short time. Treatment BF resulted in the greatest increase in shear strength in topsoil for S-10 (erosion of 10 cm) and significantly decreased penetration resistance. This treatment could significantly improve soil tillage performance and facilitate the formation of a loose upper and compact lower cultivated-layer. Shear strength responded very significantly to the interactive effects of erosion and soil treatment and was more sensitive to soil treatment. These results demonstrated that erosion makes soil less sustainable by disintegrating macroaggregates, and BF is the better soil management practice to effectively improve aggregate stability of erodible cultivated purple soil.