Runoff losses of dissolved reactive phosphorus from organic fertilizer applied to sod

Fertilizers are often applied according to nitrogen requirement; however, recent evidence suggests that phosphorus (P) may pose as much, if not more, of an environmental threat. The objective of this research was to quantify the differences in phosphate phosphorus losses in runoff from two organic fertilizers (poultry litter and composted dairy manure) and one inorganic fertilizer control, applied at a uniform nitrogen rate (187.3 kg ha(-1)). The P concentration in the poultry litter (PL) was 2.5%, while the P concentration in the composted dairy manure (CDM) was 0.5%. The fertilizers were applied to run-over troughs filled with Austin clay soil planted with Bermuda grass (Cynodon dactylon L. Pers.). Water dispersion devices supplied runoff at a rate equivalent to 125 mm h(-1). Runoff was simulated for 30 min every 7 days for a period of 10 weeks. Runoff was analyzed for quantity and PO4-P concentration. Results from the PO4-P concentration and load data show that PL had greater loss during the first runoff event, while CDM did not vary significantly (p > 0.05) from the control. This pattern continued for the first 4 weeks, but during the following weeks none of the treatments showed a difference. Comparison of cumulative losses over the 10 weeks showed that PL lost a larger proportion of its initial P application than did CDM. Composted dairy manure did not have a greater cumulative loss compared to the control. Poultry litter with its high initial P concentration lost a disproportionately larger amount of PO4-P in runoff compared to CDM with its low initial P concentrations.