Bioavailable phosphorus in animal waste amended soils: using actual crop uptake and p mass balance approach.

Animal manure amended soils often contain large amounts of bioavailable phosphorus (P) and constitute high risk for the deterioration of surface water quality through eutrophication. Current standards set for the safe disposal of animal manure through soil application are based on the assumption that phosphorus in all P sources would behave similarly. The primary objective of this study was to understand the influence of P from several manure and mineral fertilizer sources applied at 0, 50, and 150 mg P kg(-1) on two measures of bioavailable P to six soils of different initial soil test P levels using corn (Zea mays L.) P uptake and an iron oxide strip method for soil analysis (FeO-P). Total net bioavailable P (TNBP) was calculated by subtracting total P uptake by corn after seven consecutive harvests in control treatments that did not receive P from the P uptake from P-amended treatments. Net biovavailable P after the first harvest (NBP1) was calculated in a similar fashion but only using data from the first harvest. Significant differences in TNBP and NBP1 were found when comparing P sources. The hog (Sus scrofa) manure had the greatest P bioavailability while turkey (Meleagris gallopava) litter had the lowest among the animal P sources across all soils and levels of P application. Significant differences were also found between soils with the highest amounts of TNBP and NBP1 found in the Woodson soil and lowest detected in the Crete soil for most P sources. The FeO-P method was useful in predicting TNBP from most P sources.