Dear Eskinder, Please go through these publications;
1.Ag.Ecosystem and Environment 2016, 229:1-12
2. Nutrient Cycling in Ag. Ecosystem 2016, 104(3): 321-340
Though exact values for export co-efficient for TP and TN in SSA are not available, but the values of USA and Canada soils have shown variation with type of crops planted, for non row and row crops, loss of P through run off, P reserves of soil and its P adsorption capacity. Values also vary with intensive agriculture and non-intensive agriculture practices
Dear Eskinder you did nice work on Borkena river and i am much interested but still want to fill the gap that is why searching for export coefficients of nutrient flow from land to water body.