Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/13/2002
Publication Date: 7/1/2003
Citation: DRAPCHO, C.M., GASTON, L.A., TAPADOR, S., KOVAR, J.L. RUNOFF PHOSPHORUS RELATED TO SOIL PHOSPHORUS IN LOUISIANA COASTAL PLAIN SOILS AMENDED WITH POULTRY LITTER. JOURNAL OF ENVIRONMENTAL QUALITY. 2003. V. 32. P. 1422-1429. Interpretive Summary: Poultry production is the largest agricultural animal industry in Louisiana, so it is vital to the state's economy. Recent research has shown that application of poultry litter for many years has led to a build-up of soil phosphorus (P) in some areas of north Louisiana. This P can negatively impact water quality in nearby lakes and streams. Sound P management on these soils requires a better understanding of the relationship between the P in the soil and P in the water that runs off the land after it rains. In this field study, we tracked two-year changes in various measures of soil P at four established pasture sites with histories of poultry litter application ranging from one year to more than 20 years. We also used rainfall simulation equipment to produce runoff that we subsequently analyzed for P. Phosphorus and organic matter in the soils increased with increasing years of litter application. When poultry litter was applied for more than 12 years, an increase in soil P could be detected below the topsoil layer. Very little sediment was found in the runoff water, so that nearly all of the P was in dissolved form, which more easily travels in streams and rivers. Among the various measures of soil P, resin-exchangeable P and desorbable P were the best indicators of runoff P. The superior predictive ability of these methods warrants further study and refinement, since the procedures would be difficult for a soil testing lab to routinely run. Given the current emphasis on development of a State P Index and criteria for Total Maximum Daily Loads (TMDLs), this information will assist producers in managing, utilizing, or marketing the nutrients in poultry litter.
Technical Abstract: Long-term application of poultry litter has led to a build-up of phosphorus (P) in the surface layer (0-15 cm) of certain Coastal Plain soils in north Louisiana. Sound P management on these soils requires a better understanding of the relationship between surface soil P and runoff P for the soils and environment in the region. In this field study, we tracked two-year changes in total P, total inorganic P, available P (Bray 1 P, Bray 2 P, Mehlich 3 P), and resin-exchangeable P on four established pasture sites with histories of poultry litter application ranging from one year to more than 20 years. Three replicated plots at each site were subjected to a series of three simulated rainfalls, and concentrations of dissolved and total P in runoff related to the measures of soil P. Runoff P was also related to P desorbed from surface soil samples in a miscible displacement experiment. Soil P and organic matter content increased with increasing years of litter application. The increase was most evident in the 0-5 cm layer; however, movement into the subsoil (5-15 cm) occurred after 12 years of litter application. Among the various measures of soil P, only resin- exchangeable P and desorbable P consistently decreased during the two- year course of this study. An average of 96% of the P in the runoff was in dissolved form, rather than particulate form. Resin-exchangeable P and desorbable P were the best indicators of runoff P, accounting for 54% and 70%, respectively, of the variability in the data. Given the current emphasis on development of state P Indices and Total Maximum Daily Loads (TMDLs), this information will assist producers in managing, utilizing, and marketing the nutrients in poultry litter.