Potential environmental risk of the phosphorus status in soils receiving poultry manure applications in Mississippi

Author(s): Ramirez-Avila, J.; Oldham, J.; Kingery, W.; Crouse, K.; Ortega-Achury, S.

Phosphorus (P) enrichment of surface and ground water involves a combination of source factors such as high soil test phosphorus (STP) levels and site-specific soil and field characteristics that influence P transport by water flow overland and through the soils. Long-term applications of manure have generally increased STP levels to a greater degree than has fertilizer application because manure applied to meet the nitrogen (N) needs of crops provides more P than utilized by crops. Preliminary research found that subwatersheds within the poultry production counties in Mississippi have a high potential for soil and water degradation from manure P and N. An assessment was developed to increase understanding of STP levels in soils of the top 20 poultry production counties in Mississippi. The study performed a descriptive summary and analysis of temporal dynamics of STP in 15,057 soil samples, submitted for forage and pasture crop recommendations, after analysis by the Mississippi State University Extension Service Soil Testing Laboratory for 10 annual periods from 2002-2003 to 2011-2012. There were gradual annual changes in STP level ranges from the first (5 to 3780 lb ac-1) to the last year (5 to 3980 lb ac-1). Individual peak STP values of 5990 and 4840 lb ac-1 were observed in the 2nd and 7th year, respectively. However, mean STP levels increased from 113 lb ac-1 to 302 lb ac-1 from the first to the last year with the highest mean STP level of 356 lb ac-1 in the 7th year. The MSU Extension Service would not recommend additional external P for 69% of the soils sampled in the last year of the dataset; in the first year this value was 38%. These results indicate increased STP in these soils that could contribute P to runoff and leaching flows. Because of the susceptibility of these areas to manure source P leaching and runoff, Best Management Practices should be implemented that manage P source and off-field transport to minimize environmental impacts. Balancing P inputs with crop removal is an essential part of a sustainable practice to controlling P losses. Maintaining moderate STP levels or reducing high STP levels can reduce the potential for transport of P from both particulate and dissolved P. Comprehensive nutrient management plans should be developed and implemented for all poultry production operations for the optimal use of poultry manure.

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