Availability of poultry litter compost P to fescue compared with triple super phosphate

Phosphorus-based nutrient management requires that all sources of P added to fields, including manures, must be accounted for in crop production plans. Nearly 13% of U.S. broiler production occurs in the Mid-Atlantic region, which generates 720,000 tons of manure annually. Use, treatment, or manure disposal options are important issues in dealing with large volumes of manure; transforming the manure to compost and utilizing it off-farm is one viable utilization option. A study to evaluate plant-available P in poultry litter compost (PLC) compared with triple super phosphate (TSP) was conducted in a growth chamber using fescue (Festuca arundinacea Schreb). Phosphorus amendments from 0 to 150 mg P kg(-1) soil were added to Sassafras soil (typic Hapludults, fine-loamy, siliceous, mesic). Nitrogen rates were constant over all P treatments at 150 kg N ha(-1). Fescue was harvested three times during an 84-day study, and clippings, as well as roots and crowns at the termination, were analyzed for P content. Cumulative dry weight of fescue clippings was the same for both TSP and PLC and did not change with increased P application from 0 to 150 kg P ha-1 soil. These data suggest that the Sassafras soil was not deficient in P (Mehlich 3 extractable P was approximately 125 mg P ha(-1)) and that the N application rate of 150 kg N ha-1, which was constant across all P treatments, determined yields. Cumulative phosphorus uptake was the same for PLC and TSP but, in this case, was linearly related to P application rate. At the 84-day harvest, greater P uptake was recorded for 100 and 150 kg PLC-P ha-1 rates than for all other treatments, which suggested that organic compounds in the PLC may be blocking adsorption sites and/or releasing soluble P with time. Phosphorus uptake by roots and crowns was approximately equal to cumulative P uptake of clippings. Statistical analysis indicated no effect of P source or rate on P uptake by roots and crowns, but only two of four replicates were harvested. Because PLC was equal to TSP in supplying P to fescue, composting of poultry litter does not seem to affect P availability in the same manner as it affects N. Compost application based on crop N needs and N availability will result in greater plant-available P additions than if uncomposted poultry litter is added.