Scale-Related Variations in Soil Loss and Validation of the RUSLE Model in Anambra State, Nigeria

Soil erosion is a severe environmental problem in Anambra State but insufficient data hampers effective conservation and planning. Hence, in-situ measurements were done during the 2022 rainy season to assess erosion responses to changes in vegetation cover, slopes, scale, and soil characteristics. Runoff plots were set up in Isu-Aniocha, Aguleri, and Oko. Soil loss was 0.74 kg m^–2 mon^–1 in Oko, 0.36 kg m^–2 mon^–1 in Aguleri, and 0.09 kg m^–2 mon^–1 in Isu-Aniocha. Soil loss per unit of rainfall was 0.37 kg mm^–1 (Oko), 0.08 kg mm^–1 (Aguleri), and 0.04 kg mm^–1 (Isu-Aniocha). The erosion rate was 6 times higher on bare plots than on vegetated plots. The RUSLE model performed relatively well in the area. The soil erosion rate from the RUSLE model has a percentage bias of 9.04% indicating a little underestimation of soil erosion in the area. Soil loss rate is higher on small plots, but the reverse is the case when the gross soil loss is considered. Time is critical to erosion occurrence in the State as the worst erosion scenarios occurred in the last month of the season. Therefore, effective soil conservation measures should be prioritized toward the end of the season. Also, soils should be protected with vegetation and other covers.