Scale-dependence of soil erosion assessments based on the distribution of sugarcane cropping practices in Okinawa, Japan

Abstract

Accurate soil erosion estimations are required for both economic and ecological purposes. In sugarcane fields on Ishigaki Island, Japan, several types of cropping practices are undertaken in the same region and annual cropping practice distribution changes (ADCs) occur. ADCs suggest that the dynamics of soil erosion from sugarcane fields differ year by year. In this study, we evaluated the annual soil erosion errors derived from ADCs by reconstructing a map showing the distribution of cropping practices among sugarcane fields, calculating soil erosion using the Universal Soil Loss Equation (USLE), and determining the coefficient of variation (CoV) as an indicator of errors. The CoV was large, especially at the scale of 0.001–3 km². A comparison with previous research also indicated that the errors derived from ADCs had a larger impact on soil erosion estimations than those from the USLE properties, at least at scales smaller than 0.1 km², suggesting that an appropriate consideration of ADCs is required for accurate soil erosion estimations.