Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 14, 1996
Publication Date: N/A
Interpretive Summary: Poultry production is of major economic importance to an increasing number of states in the U.S. However, the concentration of broiler operations in localized areas often generates amounts of nitrogen and phosphorus in litter (manure plus bedding material) that exceed local crop requirements. When continual land application of poultry litter exceeds crop nutrient requirements, enrichment of nitrates in ground water and phosphorus in surface water can occur. Thus, several states are developing guidelines for litter management based on environmental as well as agronomic criteria. Although the rate and method of litter application is considered, farmers often have less flexibility as to when the litter is applied. Even so, if litter is applied during periods of the year when intense storms are likely, more nitrogen and phosphorus can be lost in runoff. We found that as the length of time between litter application and rainfall increased, the loss of nitrogen and phosphorus in runoff decreased. For phosphorus, this decrease in loss was greater for soils that could sorb large amounts of phosphorus applied in the litter. This information will aid development of more flexible recommendations for poultry litter application by selection of fields with soils less affected by rainfall frequency and timing.
Technical Abstract: Large amounts of manure produced in confined animal operations can be a valuable nutrient source for local crops. However, repeated land application of manure has enriched nitrogen (N) and phosphorus (P) in runoff in certain areas. In these areas, more restrictive manure management guidelines may be adopted. The main factors affecting N and P loss in runoff from land receiving manure include the rate, method, and timing of application. Of these factors, least information is available on timing, thus, the effect of rainfall frequency and timing (2.54 cm/h) after poultry litter application (10 Mg/ha; ie., 380 kg N and 160 kg P/ha) on N and P transport in runoff was investigated for 10 Oklahoma soils. The concentration of N and P in runoff decreased with 10 successive rains, 7 days after litter application. Although the decrease in N concentration was independent of soil type, decreases in dissolved P (DP) and bioavailable P (BAP) were related to percent saturation of soil P sorption sites (r2 of 0.97 and 0.62, respectively). Increasing the time between litter application and rainfall from 1 to 35 d reduced total N from 7.54 to 2.34; ammonium-N (NH4-N), 5.53 to 0.11; DP, 0.74 to 0.45; and BAP, 0.99 to 0.65 mg/L. These decreases are attributed to leaching and volatilization of N and sorption of P. Nitrate-N (NO3-N) concentrations were unaffected by rainfall frequency and timing. The loss of N and P in runoff may be minimized by avoiding manure applications during periods of high rainfall probabilities. Further, these reductions will be greater for high than low P sorbing soils.