Sediment Discharge from a Ridged Field with an Andisol

Soil erosion in ridged field plots with Kuroboku soil, an Andisol, was observed between May and October for 3 years at a cropland site in northwest Kanto, Japan. The amount of sediment yield from the plot planted with cabbage was much less than that from the bare plot. The observed results suggest that the rates of ridge erosion, detachment, and transport of soil particles due to surface runoff in the furrow channels of the planted plot were less than those of the bare plot. Soil erosion on the bare plot during most events was a transport-limited process. The Yang sediment transport equation effectively estimated the sediment yield from the bare ridged plot with Kuroboku soil when a transport-limited process was considered to be dominant. The equation is likely to be suitable to estimate the sediment transport capacity of furrow channel flow for the study soil. The equation overestimated the sediment yield for the planted plot. To estimate sediment yield for the planted ridged field in the study site, soil erosion Soil erosion by water is a frequent problem in agricultural fields in northwest Kanto, Japan. The region is an agricultural area where cabbage and other vegetables are produced under cool summertime conditions. The site is in a mountainous area, with elevations ranging from 700 to 1,400 m and rolling topography. The dominant soil in the region is Kuroboku soil, an Andisol. The soil is a volcanic ash soil with an organic matter content of 10% or more, low in bulk density, and easily erodible. Heavy rains in the rainy season, showers in the summer, and typhoon rains in the autumn cause soil erosion. This erosion results in a loss of topsoil, and the suspended load in streams resulting from the erosion may damage downstream water quality. The planning and design of erosion control measures require quantitative information on sediment yield from fields. Soil erosion models based on hydrological and erosion processes (Nearing et. al, 1989; Morgan, 1994) are valuable tools for estimating sediment yield from cropland fields for the planning and design of erosion control measures. Recently, Nakao et al. (1996) and Takagi et al. (2001) assessed the efficacy of soil erosion models on a field scale in Japan. However, few studies have been conducted to estimate soil erosion or to obtain sediment yield characteristics on cropland fields in this region with Kuroboku soil by using such models. The objective of this study was to clarify the fundamental characteristics of soil erosion on a cropland field in this region through field plot observation and to discuss the applicability of the Yang sediment transport equation (Yang, 1973) for estimating sediment yield. The results of this study will make it possible to develop a method for sediment yield prediction for cropland fields with Kuroboku soil.