Effects of Rainfall-Induced Topsoil Structure Changes on Root-Zone Moisture Regime during the Dry Period

Abstract

Rainfall erosion and subsequent intermittent drought are serious barriers for agricultural production in the subtropical red soil region of China. Although it is widely recognized that rainfall-induced soil structure degradation reduced soil water storage and water-holding capacity, the effects of variation of the rainfall-induced topsoil structure on the subsequent soil water regime during the dry period is still rarely considered. The objective of this study was to ascertain the way of rainfall-induced topsoil structure changes on the subsequent soil water regime during the dry period. In a three-year-long experiment, six practices (CK, only crop; SM, straw mulching; PAM, polyacrylamide surface application; B, contour Bahia-grass strip; SPAM, straw mulching and polyacrylamide surface application; and BPAM, contour Bahia-grass strip and polyacrylamide surface application) were conducted at an 8° farmland with planting summer maize resulting in different topsoil structure and root-zone moisture, to establish and reveal the quantitatively relationship between the factors of topsoil structure and soil drought. Rainfall erosion significantly increased the soil crust coverage, and decreased the WSA0.25, 0–30 mm soil porosity and mean pore size. There was no significant difference during the raining stage of root-zone water storage between CK and other practices. An index of soil drought intensity (I) and degree (D) was established using soil water loss rate and soil drought severity. The larger value of I means a higher rate of water loss. The larger value of D means more severe drought. During the dry period, I and D were significantly higher in CK than in other practices. I and D had significantly positively correlation with the crust size and crust coverage, and negatively with WSA0.25, 15–30 mm soil porosity and mean pore size. Among of soil structure factors, the soil porosity had the largest effect on I and D. The rainfall-induced topsoil structure changes greatly deteriorated the root-zone regime during the dry period mainly due to significant increasing soil water loss but little improving the raining stage of soil water storage. Straw mulching had greater effects than other practices in alleviating rainfall-induced erosion and intermittent drought, and could be a better strategy applied for this region.