Effect of Composted Manure Incorporated in the Top Soil on Interrill Erosion.

Runoff sediment generated from manured soil enhances nutrients transport in cultivated area. In this study, we focused on the effect of incorporated composted cattle manure on runoff and sediment generation from bare Andisol (clay loam) under simulated rainfall. Specifically the interaction between an interrill erosion and conditions of top soil which is modified by different application rates and incorporation depth of the compost was investigated. Treatments designed were : 1) application rate of 0 Mg ha^-1 as a control, 2) 16 Mg ha^-1 (dry basis) with incorporation depth of 8 cm, 3) 8 Mg ha^-1 with incorporation depth of 4 or 8 cm, 4) 4 Mg ha^-1 with incorporation depth of 4 cm,  or 0 cm (i.e. surface applied). Each treatment was prepared in a small soil pan (50 cm by 20 cm by 11 cm) with a slope of 7 % and subjected to simulated rainfall of 36.8 mm hr^–1 for approximately 100 minutes. Time to runoff initiation, runoff rate, sediment yield rate and electrical conductivity (EC) were measured. The results showed no significant change in time to runoff and steady state runoff rate among all the treatments except the soil with surface applied compost that delayed runoff initiation about 20 minutes. Interrill erosion was unaffected by compost incorporation manners, however, was greater than the surface applied condition. Exceptionally the soil with 16 Mg ha^-1 of compost incorporation, which resulted in the highest sediment concentration and corresponding EC just after runoff initiation, showed greater sediment loss than the control.