Reduction of nitrogen losses through erosion by Leonotis nepetaefolia and Sida acuta in simulated rain intensities

Leonotis nepetaefolia, a tall herb and Sida acuta a medium size herb were selected to experimentally test the efficacy of vegetal cover in conservation of soil, water and nitrogen under varying intensities of simulated rain. Young seedlings of the species collected from the banks of the Rihand River, about 150 km South of Varanasi, India, were transplanted on sloping experimental plots. Simulated rainfall of 20, 25, 31, 38, 46 and 55 mm h(-1) was applied for 50 min on the two vegetated and one bare plot. Water and soil running down from each of the sloping plots were collected separately in respective cemented reservoirs. They were analysed for different forms of nitrogen. The conservation value (Cv) of soil, water and nitrogen were calculated using Ambasht's formula. Depending upon the nature of vegetation protecting the surface, soil loss through erosion increased two to three times on doubling the rain intensity. As the rain intensity was raised soil conservation value of Leonotis increased from 63 to 88% and of Sida from 27 to 57%. Leonotis with better ground cover reduced particulate nitrogen erosion more effectively. The major fraction of nitrogen (total-N, ammonia-N and nitrate-N) transport down the slope was in soluble form. (C) 1997 Elsevier Science B.V.