Characteristics of vertical runoff output on red-soil slope under natural rainfall condition

Abstract: Surface runoff, interflow and underground runoff are components of runoff on sloping land, which exert an important impact on runoff generation and nutrient loss at watershed scale. This study was conducted to analyze the characteristics of vertical runoff output in different soil strata on a red-soil slope under three conditions: vegetation coverage, litter mulch, and bare land for three years from 2010 to 2012. The study area lies in Jiangxi Provincial Eco-Science Park of Soil and Water Conservation (29°16′37″-29°17′40″N, 115°42′38″-115°43′06″E), which is located in Boyang River watershed of Poyang Lake Basin, in De'an County, Jiangxi Province, China. This region is characterized by a subtropical humid monsoon climate with mean annual precipitation of 1397.3 mm. The soil is red soil. In order to investigate characteristics of runoff output in different soil strata on the red-soil slope with drainage lysimeter, the experiment was laid out using three 5 m × 15 m plots with slope of 14°. The treatments were 1) planted Bahia grass, 2) mulching dry Bahia grass, and 3) bare land. There were four discharge outlets used to collect surface runoff: interflow 30 cm underground, interflow 60 cm underground, and underground runoff 105 cm underground in each plot. The results showed that the total runoff of litter mulch treatment was maximum, followed by the bare land, and the vegetation coverage treatment under natural rainfall conditions. Besides, surface runoffs of vegetation coverage and litter mulch treatment were far less than that of the bare land treatment, which were 7.9% and 9.8% of bare land, respectively. It indicated that the planted grass and the litter mulch can reduce surface runoff significantly. Interflow of the bare land treatment was the least, which was respectively 56.4% of the vegetation coverage and 35.6% of the litter mulch treatments. It demonstrated both vegetation and litter can increase water seepage. Underground runoff of the vegetation coverage and the litter mulch treatments were both above 90% of total runoff output and the bare land accounted for 68.4% in the three years. For the three treatments, the amounts of surface runoff, interflow and underground runoff and total runoff were the highest in the spring, accounting for 37% to 49% of the whole year, followed by summer (26%-37%), but they were lower in autumn and winter. This phenomenon was attributed to annual precipitation that was mainly concentrated in spring and summer in Jiangxi Province. On a small scale, whether by annual or monthly runoff analysis, underground runoff was the main way of runoff output on red soil slope under different treatments, and interflow and surface runoff were directly related to the presence or absence of ground coverage. Measures of vegetation coverage and litter mulch can be taken to reduce surface runoff, conserve water, increase seepage and change surface water into underground water. The research can provide references for reducing soil erosion and making full use of soil and water resources on red-soil slope.