Sequential Fractionation and Water Soluble Phosphorus Methods to Investigate Soil Phosphorus in a Long-term Manure Application.

Animal manure can enhance crop production if properly managed, as a source of plant nutrients and organic matter. However, if mismanaged, manure applications may be detrimental to environmental quality. A significant concern about manure application is the increase of soil phosphorus (P) as well as soluble P transport to surface waters that may also contribute to water eutrophication. The objectives of this study was to evaluate how long-term manure applications affect the amount and partitioning of bioavailable P and water soluble P (WSP) levels at five depths (0-120 cm) in the soil when using different N sources (beef manure, swine effluent and urea) for plant nutrients. A modified soil phosphorus fractionation procedure modified from Hedley et al. (1982) as well as Tiessen and Moir (1993) was used to determine the various P forms found in soil where several different types of animal manure were used. In this procedure, sequential extraction using H₂O, NaHCO₃, NaOH, HCl and concentrated HCl were combined to analyze total and inorganic P; organic P was determined by the difference between total P and inorganic P in each extract. Soil samples were taken from continuously cropped, conventionally tilled maize (Zea mays L.) production experiment that was initiated in 1995 in Goodwell, Oklahoma. Results show that WSP increases were greater for beef manure at the surface than for other N sources; however swine effluent and urea showed increases to WSP at the depth 20-60 cm. Sequential fractionation showed that this increase of WSP was primarily due to P movement during irrigation events. The importance of this field study was to assess the P movement and fate from long-term established animal manure management in semiarid ecosystems.