Tillage and nutrient source effects on surface and subsurface water quality at corn planting

This study quantified the effects of tillage (moldboard plowing [MP], ridge tillage [RT]) and nutrient source (manure and commercial fertilizer [urea and triple superphosphate]) on sediment, NH4+-N, NO3--N, total P, particula te P, and soluble P losses in surface runoff and subsurface tile drainage f rom a clay loam soil. Treatment effects were evaluated using simulated rain fall immediately after corn (Zea mays L.) planting, the most vulnerable per iod for soil erosion and water quality degradation. Sediment, total P, solu ble P, and NH4+-N losses mainly occurred in surface runoff. The NO3--N loss es primarily occurred in subsurface tile drainage. In combined (surface and subsurface) now, the MP treatment resulted in nearly two times greater sed iment loss than RT (P < 0.01). Ridge tillage,vith urea lost at least 11 tim es more MH4+-N than any other treatment (P < 0.01). Ridge tillage with manu re also had the most total and soluble P losses of all treatments (P < 0.01 ). If all water quality parameters were equally important, then moldboard p low with manure would result in least water quality degradation of the comb ined now followed by moldboard plow with urea or ridge tillage with urea (e quivalent losses) and ridge tillage with manure. Tillage systems that do no t incorporate surface residue and amendments appear to be more vulnerable t o soluble nutrient losses mainly in surface runoff but also in subsurface d rainage (due to macropore nov). Tillage systems that thoroughly mix residue and amendments in surface soil appear to be more prone to sediment and sed iment associated nutrient (particulate P) losses via surface runoff.