Modeling Phosphorus Dynamics in and Losses from Soils Amended with Cattle Manures and Chemical Fertilizers Using Surphos.

An important source of P loss in surface runoff is surface applied manure/fertilizer; however, few models simulate the direct transfer of phosphorus (P) from manure/fertilizer applied on the soil surface. We tested SurPhos with field experimental data of different manure/fertilizer application in a clay loam soil. Nine periods from 2008 to 2010 covering growing season were chosen for simulation. Simulated manure water extractable P (WEP) lost in surface runoff occupied 35%-44% of total dissolved P (TDP) lost in surface runoff under solid cattle manure treatment. While under liquid cattle manure treatment, simulated manure WEP lost in surface runoff occupied 31%-70% of TDP lost in surface runoff. Simulated labile P2 as soil layer of 0-15 cm was reasonable comparing with measure Olsen P. Simulated labile P1 at soil layer of 0-2 cm and P2 showed conversely trend. Simulated WIP (water extractable inorganic P) showed more obvious decline according to rainfall events. Simulated P sorption coefficient showed a decreasing trend with time during all the experiments. Simulations of all four categories, i.e. solid (R² of 0.88) and liquid (R² of 0.82) cattle manure, fertilizer P (R² of 0.95), and no P fertilization/soybean year (R² of 0.79) were all shown reliable results. Nash-Sutcliffe efficiency (NSE), percent bias (PBIAS), and the ratio of root mean square error to observation standard deviation (RSR) were all under reasonable range. SurPhos thus presents a reliable prediction of manure/fertilizer P loss in surface runoff and quantifies different sources of P loss and dynamic labile P in soil.