SOIL EXTRACTABLE PHOSPHORUS CHANGES WITH TIME AFTER APPLICATION OF FERTILIZER: I. LITTER FROM POULTRY-FED MODIFIED DIETS a.

Recent studies have suggested that best management practices, such as dietary modification, used to reduce phosphorus (P) in litter may increase P runoff from pastures fertilized with litter. The objective of this study was to determine the effects on soluble P, Mehlich 3 P, Morgan P, or Olsen P with time as the result of fertilization, using litter from dietary modification and from litter amendment treatments. Poultry litter and inorganic fertilizer additions to high and low soil test P (soil test phosphorus, STP) soils resulted in an increase in all P fractions as compared with unfertilized soil. Soluble P in soils increased until about week 4 or 8 after additions of poultry litter. There were no appreciable changes in Mehlich 3 P with time in high STP soil; however, there were significant decreases in Mehlich 3 P when low STP soils were fertilized with poultry litter and inorganic fertilizer. Use of dietary modification (phytase and/or HAP corn) tended to cause slight to moderate reductions in extractable P compared with a normal diet, whereas addition of alum to poultry litter tended to result in significant reductions in the various P fractions analyzed. The P sorption ratio (phosphorus sorption ratio, PSR) was also increased by inorganic and poultry litter fertilizer treatments, although in both high and low STP soil, use of HAP corn, phytase, and alum resulted in similar PSR values compared with unfertilized soils. Results from this study indicate that poultry producers should use dietary modification and alum to maximize the ability of their soils to receive poultry litter as a valuable fertilizer resource.