Submitted to: Agricultural Experiment Station Publication
Publication Type: Abstract Only
Publication Acceptance Date: November 1, 2007
Publication Date: November 20, 2007
Citation: Schwartz, R.C. 2007. Seasonal and long term changes in manure phosphorus availability. Nutrient Management Training, November 20, 2007, Texas A&M Research Center, Amarillo, Texas. Technical Abstract: Soils are most often the resource used in the final assimilation of many agricultural waste products. In regions where manure phosphorus (P) production exceeds the assimilative capacity of crops, soil P will often accumulate at high levels. Land application of manure at rates exceeding crop removal can change soil phosphorus chemistry and increase soil P to levels that are of environmental concern. Soil test phosphorus can detect changes in extractable P but provides little information on the factors that control P transport from soil to water. In contrast, a soil P index approach to managing biosolid applications also considers application rate, runoff, and soil erosion effects in evaluating the potential for P loss in a field. The Texas NRCS Nutrient Management Standard (Code 590, 2007) sets the threshold level of soil test P at 350 ppm in western Texas counties and places additional restrictions on maximum P application rates when this level is exceeded. Soil test P increases slowly with time in response to manure applications. However, soil test P also declines slowly in response to crop uptake. For example, reducing Mehlich 3 P from 350 to 100 ppm with continuous, irrigated corn could take as much as 28 years in a fine textured soil. Periodic soil testing is required to track long-term changes in extractable P to assist in making wise nutrient management decisions.