Predicting the Safe Phosphorus Storage Capacity of Sandy Soil Profiles. (S11-nair616192-poster)
Authors:
V.D. Nair* - University of Florida W.G. Harris - University of Florida D.A. Graetz - University of Florida
Abstract:
Standard soil test extraction methods (e.g. Mehlich 1) have been adapted for protocols assessing environmental risks of phosphorus (P) loss from soils. However, a low Mehlich 1-P does not indicate that the soil has the capacity to retain significant amounts of P added as fertilizer or animal waste.
Spodosols of the Lake Okeechobee basin for example, if not previously loaded heavily with P, would have a low fertility index risk rating at the outset, but would quickly reach high-risk levels with P loading due to low retention capacity. We assessed the remaining P capacity of soils under dairy operations in the Suwannee River and the Okeechobee Basins of Florida by calculating of the ratio of extractable P (Mehlich 1-P) to the sum of Mehlich 1-(Fe+Al). We assumed a theoretical value of 0.15 as the maximum safe saturation capacity of a soil, the remaining capacity for a given soil layer can be calculated as (0.15 - measured ratio)*(Fe+Al), where Fe and Al are Mehlich 1-extractable iron and aluminum. The 0.15 maximum capacity ratio has been calculated based on earlier research on Florida soils. The remaining capacity of a soil (mg P kg -1) may then be converted to kg P ha -1 or in pounds acre -1 by taking into consideration the bulk density of a soil (we have taken an average value of 1.5 g kg -1) and the depth of the surface horizon (currently taken as 15 cm). A greater depth range could be accounted for in soils where leaching is >> surface runoff.
Speaker Information: Vimala Nair, University of Florida, 106 Newell Hall, Univ. of Fl P.O. Box 110510, Gai, Gainesville, FL 32611-0510; Phone: 352-392-1804 x 324; E-mail: [email protected]
Session Information: Monday, November 3, 2003, 4:00 PM-6:00 PM Presentation Start: 4:00 PM (Poster Board Number: 1432)
Keywords: depth evaluation; phosphorus saturation; phosphorus loading; environmental risk assessment
