Phosphorus Characterization of Alabama Soils Under Different Management Practices for Environmental Risk Assessment.

Continuous application of fertilizers and manure in excess of plant requirements leads to buildup of phosphorus (P) in soil. Excess soil P is susceptible to loss and promote eutrophication of water bodies. Soil test phosphorus (STP) originally developed for agronomic purpose is used as an indicator of environmental P loss risk. However, STP is not a true indicator of P loss risk. Degree of phosphorus saturation calculated from acid ammonium oxalate (DPS_ox) is another tool used for assessment of P loss. However, oxalate extraction is not a routine soil test due to the length of time and reaction conditions required. There is a need to follow a standard rapid soil testing protocol to determine the environmental P loss risk from Alabama soils. Phosphorus saturation ratio (PSR) calculated using Mehlich 1 (PSR_M1) and Mehlich 3 (PSR_M3) defined as the molar ratio of extractable P to extractable Fe +Al, can be used as an easy mean for predicting P loss risk. The objective of this study are to determine and compare the environmental risk of P loss for Alabama soils under different management practices using the concept of PSR_M1, PSR_M3, and DPS_{ox .} Soil samples were collected to a depth of 0-60 cm across different manure application history, and soil types from different farms in Alabama. Water soluble phosphorus (WSP), Mehlich-1, Mehlich-3 and Oxalate extractions were carried using standard procedures and DPS and PSR were calculated. For most of the surface soils (0-5 cm), PSR and DPS values were greater than the threshold limit (a critical point beyond which WSP increases abruptly) and the magnitude differed between soil types, manure history and farm operation. Preliminary results indicate that PSR_M3 values were closely related to DPS_ox and can be used as means for predicting environmental P loss risk for soils of Alabama.