Submitted to: Mississippi Water Resources Research Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 8/15/2000
Publication Date: N/A
Interpretive Summary: Poultry litter (bird manure with bedding materials) has been applied to some farm fields for over 50 years in Mississippi. One of the results of continued litter applications is the accumulations of some plant nutrients to levels that they are potentially polluting to our streams and ponds. To remove some of the nutrients from the soil, hay can be grown on the land, harvested, and sold to farmers at other locations. The concentration of nutrients in the soil is reduced by whatever nutrients have been removed in the harvested hay. Potentially, if more hay is grown on the fields, more nutrients can be extracted from the land. Irrigation and or nitrogen applications might improve the forage growth and increase the amounts of phosphorus extracted. In this research, irrigation and nitrogen fertilizer did increase the amounts of hay removed, but the amount of phosphorus removed was increased only by the irrigation. Suprisingly, the addition of other fertilizer, in this case nitrogen, seemed to cause a dilution of phosphorus in the plant not found with irrigation. Thus the relationship of nutrient concentrations to farm management appears to be much more complex than anyone had expected.
Technical Abstract: Poultry litter has been land applied for over 50 years at some sites in Mississippi. The possiblity of phosphorus pollution of ponds is increased as the phosphorus concentrations of the fields in a watershed increases. Efforts are now made to remediate these fields by growing forages on the land and removing the excess phosphorus in the hay which is cut and fed to animals at other locations. Forage yields may be increased by more application of organic or inorganic fertilizer and by applications of irrigation when moisture is limiting. Litter was applied at rates of 9 and 18 Mg/ha, with ammonium nitrate applications of 67.2 Kg/ha on half of the plots and no nitrogen on the other plots, and irrigation at 3 cm/week on half of the plots when rain did not occur the previous week. Forage yields were increased by applications of 18 Mg/ha of poultry litter, 67.2 Kg/ha nitrogen, and by irrigation. In contrast, phosphorus removal was increased significantly only with the irrigation. The application of inorganic nitrogen and more poultry litter resulted in lower concentrations of phosphorus in the hay and the result was insignificant increases in total phosphorus removal. The effects of irrigation include making the hay yields(and phosphorus removal) much more predictable. Though only two years of this study have been completed, these results indicate a complex and sometimes antagonistic relationship between nutrients in the soil and nutrient concentrations in the plants.