Abstract: Grass barriers (0.8-1.2 m in width) combined filter strips are generally considered to be an effective way in reducing nitrogen and phosphorus under gentle slopes (4% to 6%). Is this the case for the combined filter strips in nutrient removal with increasing filter slopes? We made a comparative study in reducing nitrogen and phosphorus between Vitex negundo strips (2 m×8 m) and V. negundo strips (2 m×7 m) combined Miscanthus floridulus strips (2 m×1 m) under three filter slopes (5%, 10% and 15%). The results showed that the removal efficiency of combined filter strips and V. negundo filter strips in total N, NH₄⁺-N, NO₃^--N and total P decreased as the slope increased from 5% to 15%. The removal efficiency was generally higher in combined filter strips than in V. negundo filter strip regardless of filter slopes. Our results can advance the knowledge regarding the effect of grass barrier-combined filter strip on the water quality protection, having implications for reducing nonpoint-source pollution in agricultural areas.

Key words: yield, deficit irrigation, shading, water and radiation coupling., Coffea arabica