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Abstract
Soil mechanical properties are crucial for plant growth, soil erosion, tillage and traffic. The soil mechanical properties and stability of an Ultisol were determined in a 13-year fertilization experiment in subtropical China. The effect of organic matter on soil structure was also evaluated.
The treatments include: unfertilized, mineral fertilized, mineral mixed with straw, and animal manure. Bulk soil strengths (shear strength and penetration resistance) were tested in field. Aggregate strengths (penetration resistance and tensile strength), water stability, organic carbon (OC), hot-water-extractable carbohydrate (HWEC) and some related factors were determined in laboratory.
Fertilizer increases aggregate penetration resistance, tensile strength, water stability and organic matter content in cultivated horizon (0-15 cm depth), especially at the 0-5 cm layer. OC and HWEC showed significantly regression relationships with aggregate water stability, porosity and water repellency for the whole soil profile (0-40 cm). Aggregate strengths also increased with OC and HWEC in cultivated horizon.
Animal manure is most effective in improving soil structure while aggregate water stability is the most sensitive index of fertilizer management. Soil organic matter is a strong determinant of soil structure. Both OC and HWEC are good indicators of surface aggregate strengths and stability, and thus, soil quality in this region.[PUBLICATION ABSTRACT]