NITROGEN AND PHOSPHORUS AVAILABILITY IN ENRICHED, PELLETIZED POULTRY LITTERS

The highly concentrated nature of the poultry industry on the Delmarva (Delaware-Maryland-Virginia) peninsula, an area dominated by sandy soils and shallow groundwaters, has raised serious questions about possible ground and surface water contamination from N and P in poultry wastes. When poultry litters and fertilizer sales are combined an average excess, beyond the requirements of agricultural crops, of 48 kg N/ha and 16 kg P/ha is estimated to occur in Delaware annually. Movement of excess poultry wastes to areas of nutrient deficiency is often hindered by their low nutrient content and physical properties. Because manures (and other wastes) are usually wet, bulky materials with low concentrations of the major plant nutrients (N, P, K), large volumes must be handled and transported to provide adequate nutrients for most crops. As handling and transportation costs increase, the distance of transport decreases; hence, manure nutrients are often concentrated in localized areas. Pelletization and enrichment of poultry litters with inorganic fertilizers to give higher analysis materials with physical properties more suitable for transport and application by commercial fertilizer equipment may facilitate redistribution of excess nutrients. We compared N and P availability in two commercially pelletized poultry litters (EPPLs) that had been enriched with (NH4)(2)H2PO4 and KCl with normal broiler litter (BL) and inorganic N (NH4NO3) in laboratory and greenhouse studies. Nitrogen and P mineralization rates were measured in a 16 week laboratory study with a Hammonton loamy sand and a Pocomoke black loamy sand. Nitrification occurred rapidly in both soils, but, under the static conditions of the incubation study, some mechanism of N loss from a plant-available form, possibly microbial immobilization or denitrification, resulted in an approximate 50% decrease in available N within six weeks in EPPL-amended soils. Soluble P was increased by about 20-25 mg P/kg and 7-12 mg P/kg in soils amended with EPPLs or BL, respectively, but quickly reverted to less soluble forms; little P was mineralized from added or native organic matter. Average recoveries of P added in EPPLs after 16 weeks were greater in the Pocomoke soil (15%) than in the Hammonton soil (5%), suggesting that soil organic matter may have inhibited P fixation. Results of greenhouse studies with corn and tomatoes showed that EPPLs, when applied at the correct rate, were generally more effective, consistent N sources than BL alone, and could produce comparable yields and N uptake as NH4NO3. For corn, averaged over all N rates, N use efficiency values (percentage of added N recovered by plants, adjusted for soil N uptake by plants) were 42, 74, and 48% for EPPL-1, EPPL-2, BL, respectively; for tomatoes, the percentages were 52, 69, and 9%. The N recoveries observed alleviate some concerns about N availability from EPPLs and suggest that under the dynamic conditions of the greenhouse studies, the corn and tomato plants effectively competed with the microbial biomass for N.