Physical characteristics of ultisols and the impact on soil loss during soybean (Glycine max Merr) cultivation in a wet tropical area

Abstract

Physical characteristics are among soil properties affecting the susceptibility to erosion. Determination of physical characteristics of Ultisol was aimed to evaluate the dynamics of the soil properties as well as the impact on soil erosion and runoff (RO) during soybean cultivation in a wet tropical area. Soybean was planted within erosion plots (18 m2) at 25% slope in Ultisols Limau Manis (having > 5000 mm annual rainfall).Soil samples for physical properties (soil texture, bulk density, total pore, permeability, aggregate stability,and organic carbon) as well as amount of RO and soil loss were analyzed at 5 different times (stages) during the cultivation. The results showed that there were fluctuations in physical properties of Ultisol during the cultivation. Likewise, the amount of runoff and soil loss also changed during the study. Among the physical properties analyzed, the aggregate stability index of the soil was highly correlated to the amount of RO (R2=0.73) and soil loss (R2=0.94). The amount of RO and soil loss was controlled by soybean development at the average rainfall intensity (≤ 36 mm/day), not at rainfall intensity (>36 mm/day). Thus, It is suggested not to open heavy clayey and low organic carbon (OC) soils for seasonal crop farming during rainy season in wet tropical areas.