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

Sequential fractionation and water soluble phosphorus methods to investigate soil phosphorus in a long-term manure application.
Tanganelli; Soares; Turner; Hattey.
Abstract
Repeated applications of animal manure have been demonstrated to increase of soil phosphorus (P), including water soluble P (WSP) forms which have the potential to be transported to nearby surface waters.  Manure applied to fulfill crop nitrogen (N) requirements often results in an increased buildup of soil P.  Increased total soil P elevates the risk of greater WSP which can be subsequently be transported into waterways via erosion or runoff.  The objectives of this study was to investigate soil P in a long-term manure application study using sequential fractionation with H₂O, NaHCO₃, NaOH, HCl and concentrated HCl extracts; and to evaluate how bio-available P and WSP levels from long-term manure applications have been affected when different N sources (beef manure, swine effluent and anhydrous ammonia) were utilized.  Soil samples were taken to a depth of 120 cm from a continuous cropped, conventionally tilled maize (Zea mays L.) production experiment that was initiated in 1995 at the Oklahoma panhandle Research and Extension Center (OPREC) located in Goodwill, Oklahoma.  Increases to WSP were significantly increased when soils were amended with beef manure at the surface; however anhydrous ammonia applications were similar to the control at all depth.  A slight increase to surface WSP was observed in the swine effluent applications.  All increases to surface WSP were strongly correlated to the total P additions since 1995.  Increases to WSP at 30–45 cm were also observed.  Sequential fractionation showed that this increase of WSP was primarily due to P movement due to 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.