Spatial variations in runoff, sediment, and nutrient losses induced by toposequence and biochar application in upland maize farming

Abstract

Soil erosion is a natural process that can be intensified by inappropriate land use and agricultural practices. Therefore, it is essential to gain a deeper understanding of the effects of agro-ecological practices, such as biochar application, on soil erosion processes in upland areas, particularly in Southeast Asia. Moreover, understanding the variations in erosion characteristics across a toposequence is vital for sustaining upland agriculture. The objective of this study was to investigate the effects of toposequence position and biochar application on sediment loss, runoff, and nutrient losses under natural rainfall conditions in Nan Province, Thailand. We installed 24 plots of 1 m² each, located at four positions within the toposequence. The biochar was incorporated into the soil at 5 cm depth. Over two rainy seasons, we regularly measured sediment loss, runoff, and nutrient losses on plots with and without biochar along the four positions of the toposequence. Our findings indicated that the addition of biochar amendments to the topsoil effectively reduced nutrient loss through runoff, particularly nitrogen. This practice also improved vegetation cover, increased soil moisture, and decreased the presence of free elements such as micro-aggregates, gravels, and carbon nodules (biochar) on the soil surface. During the study, we observed the re-emergence of previously integrated biochar on the soil surface after eight months under natural conditions, which manifested as a crust on the soil surface. Positions within the toposequence had a significant impact on various soil properties, including the amount of sediment loss, runoff, and nutrient losses. Therefore, considering the influence of toposequence position is essential for enhancing soil management and implementing suitable agroecological practices.