EFFECTS OF SOIL DRYING METHODS ON PHOSPHORUS FRACTIONATION IN AN AGRICULTURAL SOIL

Phosphorus is a key nutrient in many aquatic and terrestrial systems. Phosphorus fractionations are used to examine the distribution and concentrations of phosphorus in aquatic, fluvial, and terrestrial environments. Obtaining accurate phosphorus concentrations from fractionations is essential as the results can be used to assess P cycling. Along with the many accepted fractionation methods, there are different laboratory techniques for preparing soil samples such as air drying, oven drying, freeze drying, and using unpreserved samples (Styles, Coxon 2006; Dail et al. 2007). Condron and Newman (2011) suggest that pretreatments should be limited and standardized to increase cross-study relationships. Studies have been conducted to examine the effect drying methods have on the fractionation of phosphorus, concluding that oven drying (105^oC ) resulted in lower inorganic and total phosphorus concentrations (Akinremi et al. 2003, Sistani et al. 2001). Others (eg. Turner et al. 2005) have found that drying may increase the extractability of P, especially from the organic fraction.

The purpose of this study was to evaluate how different drying techniques effect the distribution of phosphorus in an agricultural soil. Sediment was evaluated using three commonly used laboratory procedures; air drying, oven drying and using soil samples maintained at original field moisture. A modified Psenner method (Noll et al., 2009) extraction was done to determine the phosphorus concentrations. Our results show statistically significant differences between the field moist samples and the dried samples for Fe-assoc., Ca-assoc. and total P. but the field moist soils had lower concentrations of extracted P as compared to the dried samples. Al-assoc. P is found to have a progression from field moist to oven dried, with oven dried having the largest amount of P removed. Field moist samples were significantly different from the oven dried samples. The air dried samples were not distinguishable from the other two sets. No difference was seen in organic matter association P. Overall, the field moist samples have a smaller range of values than either of the dried sample sets, especially for the Fe and Ca associated extractions. These results suggest that further work is needed to better elucidate the effects of drying on fractionation.