Phosphorus Leaching Losses in A Clay Loam Soil Amended with Environpig Manures.

Non-point source phosphorus (P) pollution from animal manures has increasingly become a serious global concern. Genetically enhanced pigs, Enviropigs^TM, that use efficiently phytate P in cereals and excrete manures with up to 75% reduction of P contained, provide an excellent option for reduction of P loading to water resources from agricultural farm lands. Understanding the impacts of Enviropig manure on soil P loss is essential to validate this innovative technology and to develop BMPs for best use of the manure. A study was conducted to determine soil P leaching loss in a Brookston clay loam soil using an undisturbed large soil core (30 cm d by 70 cm h) technique. Treatments included manures from four combinations of two pig genotypes (conventional pig - CPig and transgenic pig - TPig) with two diet formulas (conventional diet - CD and low P diet - LPD), and a control. All manures were added at a rate equivalent to 100 kg P ha^-1.  Leachete water samples were analyzed for dissolved reactive P (DRP), dissolved non-reactive P (DNRP), and particulate P (PP).  Manure application increased concentrations of all forms of P in soil leachete, regardless of pig genotype and diet formula. Compared with the soil amended with manure from CPig that was fed with CD, contents of leachete total P decreased by 29% in the soil amended with manure from TPig that was fed with LPD, but increased by 3% in the soil amended with manure from TPig that was fed with CD, an indication of excessive P supply. Content reduction of leachete total P was predominately accounted by DRP (72% reduction), with a small portion by PP (6% reduction). Adoption of the Enviropig technology can be an environmental friendly approach, but has to be in combination with low P diet.