Submitted to: Journal of Environmental Quality
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/13/2002
Publication Date: 9/15/2003
Citation: Tabbara, H. Phosphorus loss to runoff water 24 hours after application of manure or fertilizer: I. effects of post-application tillage and rate. Journal of Environmental Quality. 32:1044-1052. Interpretive Summary: Phosphorus added to soil from fertilizer or manure application could pose a threat to water quality leading to eutrophication of lakes and rivers even if best management practices are followed. The author used a rainfall simulator to compare concentration and losses of phosphorus in runoff water from plots that had been treated with inorganic fertilizer or liquid swine manure. A rainfall simulator applied an intense rain 24 hours after manure or fertilizer was either broadcast or disked into the soil. Results show that incorporation reduced dissolved and total phosphorus losses and concentrations in runoff water to half the values from broadcast plots. An extra tillage operation, even if cost prohibitive, could significantly reduce pollution of waterways due to early runoff, e.g when a severe storm occurs soon after application. Concentrations of dissolved and total phosphorus were greater for the higher rates of application, though similar effects were not seen with total losses due to variation in runoff flow volumes. The proportional losses in runoff water were higher from fertilizer than from manure plots. This implies that the phosphorus source is critical when evaluating nutrient budgets and related impact on water quality. These findings will help farmers as well as all those who are involved in nutrient planning and water quality protection e.g., USDA-NRCS, extension agents, and agricultural consultants, in the effort to utilize animal wastes while safeguarding our water resources.
Technical Abstract: Phosphorus (P) added to soil from fertilizer and manure application could pose a threat to water quality even if best management practices (BMPs) are followed. The objective of this study was to compare concentrations and losses of total suspended solids (TSS) and various P forms in runoff water when either liquid manure or chemical fertilizer is added to soil 24 h prior to a rainfall event. A rainfall simulation study was conducted on field plots that received two application rates of liquid swine manure or liquid ammonium polyphosphate (APP) fertilizer, using either surface broadcast or incorporated methods of application. Runoff was analyzed for TSS, dissolved reactive P (DRP), total dissolved P (TDP), total P (TP), and bioavailable P (BAP) concentrations. Results show that TSS concentrations and losses were higher in runoff from chemical fertilizer than manure plots, and concentrations were higher from incorporated than broadcast plots. Flow-weighted concentrations of all P forms were greater for the higher rate of application, but similar effects on losses were found only for BAP. Concentrations and losses of all P forms were reduced by incorporation despite an increase in sediment concentration. The study suggests higher proportional P losses in runoff water from fertilizer than manure plots; therefore P source is critical for evaluating nutrient budgets and related impact on water quality.