AVAILABILITY OF COMPOST P TO FESCUE UNDER UNLIMITED N CONDITIONS

Authors: Sikora, Lawrence; Enkiri, Nancy

Submitted to: Compost Science and Utilization
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/5/2003
Publication Date: N/A
Citation: N/A

Interpretive Summary: Farmers are advised, if not required, to submit nutrient management plans for fields they manage. Besides the amount of inorganic fertilizer, farmers must also estimate the fertilizer equivalents of manures or compost they may add to fields. Data are available on the nitrogen fertilizer content of manures and composts, but little information is available on phosphorus fertilizer content of composts. A previous study indicated that phosphorus from poultry litter compost was comparable to that of triple super phosphate. However at the termination of the study when yields were declining because of depleted nitrogen supply, fescue obtained more phosphorus from compost than triple super phosphate. This finding led to a second study to show if compost would continue to provide more phosphorus than triple super phosphate when nitrogen was not limiting. The study involved growing fescue with equal phosphorus amendments of either poultry litter compost or triple super phosphate. After two harvests, supplemental nitrogen was added and yield and phosphorus uptake was monitored. The results indicated when nitrogen is not limiting, poultry litter compost and triple super phosphate were equal in providing phosphorus to fescue. These data can aid farmers and extension agents who are required to provide nutrient management plans detailing the amount of P fertilizer applied to fields as poultry litter compost. Our conclusions are that poultry litter composts and triple super phosphate fertilizer are equal in providing P to fescue and nitrogen availability is not a factor.

Technical Abstract: Nutrient management plans require an accurate assessment of P fertilizer additions to soil. The fertilizer equivalents of manures and composts must be estimated in order to comply. A previous study comparing triple super phosphate(TSP) to poultry litter compost (PLC) in supplying P to fescue indicated that they were equal, but when N became limiting during the final harvest, PLC supplied more P to fescue than TSP at comparable rates. A subsequent study was initiated to determine if P from PLC was more available to fescue than TSP when N was not limiting. Sassafras soil was amended with PLC and TSP at rates of 0, 50, 100 and 150 kg ha-1. Nitrogen was supplied to be uniform across all treatments taking into account the N mineralization rate of PLC. Two harvests of fescue were taken and analyzed for yields and P uptake. Nitrogen was added again to all treatments at the original application rate of 120 kg ha-1 and two more harvests plus roots were collected. Yields were affected by harvest date but not affected by P rate or source of P. P uptake was affected by date and rate but not source of P. The response of fescue to PLC and TSP was curvilinear and linear respectively, but within the range of P application rates used , the source of P was not a significant factor in P uptake by fescue. Addition of supplemental N did not affect P supply from either source. Poultry litter compost is considered equal to TSP in supplying P to fescue and N availability did not affect these conclusions.