Effects of liquid swine manure placement and rate on phosphorus loss with runoff water

There is an increasing concern on the use of nitrogen (N) based manure application rate for corn production and its impact on soil phosphorus (P) buildup and the potential to release P to the environment. Therefore a field study was conducted to evaluate the effects of manure application rate and method of application on soil erosion and P loss with runoff water and sediment. Simulated rainfall was applied to 24 runoff plots to study two variables in triplicate. The first variable was application rate: liquid swine manure was applied at N recommended rate and twice the rate, and inorganic liquid fertilizer with P level that matches the amount of P supplied by manure. The second variable was placement, with manure or fertilizer either surface broadcast or incorporated;Average total runoff flow volume was found to be significantly greater for the broadcast method of manure application in comparison with the incorporated treatment. Average total runoff flow volume was also found to be greater for liquid fertilizer application treatment in comparison with manure treatment. Total suspended solids (TSS) concentrations and mass losses in runoff water were significantly greater for the liquid fertilizer treatment in comparison with manure treatment;Concentrations and total losses of all P forms with runoff water were significantly greater for fertilizer treatment in comparison with manure. These losses were significantly less when manure or fertilizer was incorporated. Concentrations of all P forms were significantly greater for the higher rates of application, but similar effects on mass losses were only found for total phosphorus, particulate phosphorus, and bioavailable phosphorus (BAP). Soil test for P (STP) by agronomic and environmental tests showed that dissolved P (DP) and BAP concentrations in runoff water were best predicted by Bray 1-P or iron oxide strip-P in soil. DP and BAP total losses with runoff water were well correlated (r \u3e 0.85) with Bray 1-P, iron oxide strip-P, and water extractable P in soil