Effect of slope position on hydrochory processes: a natural rainfall study in tropical agroecosystem

Soil erosion due to land use change and consequently biodiversity loss are major concerns in agricultural areas. However, the link between runoff, soil loss and plant dispersion by water also called hydrochory is not yet well understood, especially in tropical climate. The displacement of native plant seeds on the soil surface by runoff may be influenced by soil properties and by agricultural practices. This may in return affect or modify biodiversity in agroecosystems.This is why we propose to study the processes affecting seed displacement by runoff in steeply sloping maize field affected by rainfall and tillage erosion in Northern Thailand.After a first study under rainfall simulation in situ (Janeau et al. 2022), we present here a two years study under natural rainfall to assess the role of position in the catena and soil properties on seed displacement, soil loss and nutrient losses. We used 24 plots of 1 m2 located at four positions in the catena. Two treatments were tested: (1) conventional system with tillage and (2) biochar incorporated into the soil. We measured the displacement of seeds (only for treatment 1), runoff volume, soil and nutrient losses and soil surface features (for the two treatments) during two years of study.Preliminary results indicate a strong influence of catena position on all studied variables. This may be due to soil properties changing along the catena, as well as shape (concave or convex) of the slope position. As expected, rainfall intensity seemed influencing runoff and soil and nutrient losses, together with seed displacement.This study, under tropical climate and steep slope conditions, highlights differences in soil surface features and runoff along the catena. We should consider catena position for improving soil management and using appropriate agroecological practices.