Runoff and soil loss responses to rainfall, land use, terracing and management practices in the Middle Mountains of Nepal

Abstract

A study was conducted to assess runoff and soil loss from field plots under different land use and management practices at Pokhare Khola watershed in the Dhading district of Nepal, from 2004 to 2006. Random on-farm runoff plots were established on single and double outward sloping agricultural terraces (Bari land) with four replications of three treatments, namely: Farmer practice (Zea mays-Eleusine coracana), reduced tillage (Zea mays-Vigna unguiculata), and commercial vegetable treatment (Zea mays-Capsicum sp.). The objective was to compare efficacy of reduced tillage and cropping pattern for soil restorative management with traditional farmer practice and commercial vegetable. Additionally, two forest treatments in community-managed forest and unmanaged forest with four replicate plots were established to compare the runoff and soil loss from different forest management and land use. Results indicated that 61% of the average annual rainfall (1202 mm) eroded soil; however, annual erosivity was low to medium: 1487, 2050, and 3133 MJ mm ha-1 h-1 yr-1 in 2006, 2004, and 2005, respectively. As much as 60% of total annual soil erosion occurred in just one or two major storm events during the pre-monsoon period, when soils are bare and soils freshly tilled. The result from different land use revealed that the soil loss from agricultural land (1.3 Mg ha-1 yr-1) was higher than that in forested areas (0.3 Mg ha-1 yr-1; pB0.05), but erosion rates were lower than previously reported in the Middle Mountain region, indicating a need to re-evaluate the soil-erosion problems in this region. Although reduced tillage reduced runoff by 7 to 11% and soil loss by 18 to 28%, the study suggests that reduced tillage alone will not minimize runoff and soil loss effectively on Bari land. The relationship between soil loss and rainfall characteristics was highly variable. Ground cover and cultivation activities appeared to be the most important factors affecting soil erosion processes. © 2009 Taylor & Francis.