Runoff Losses of Dissolved Reactive Phosphorus from Organic Fertilizer Applied to Sod

Abstract

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.