Influence of Manure Phytic Acid on Phosphorus Solubility in Calcareous Soils

Manure characteristics can influence the potential for P transfer in runoff following land application of manures. This research assessed the influence of manure characteristics on P solubility in calcareous soils using manures from poultry (Gallus Domisticus) fed a variety of grain-based diets with the manures containing a range of total P (5.6-16.4 g P kg⁻¹), water-extractable P (WEP, 0.9-4.7 g P kg⁻¹), phytic acid P (0.1-7.6), total N/P ratios (2.6-5.1), and total C/P ratios (19.5-75.7). In addition, mono-ammonium phosphate fertilizer and reagent grade inositol hexaphosphate (phytic acid [PA]), were included, as well as a control treatment with no P additions. Treatments were incorporated into two soils (Portneuf [Coarse-silty, mixed, superactive, mesic Durinodic Xeric Haplocalcids] and Millville [Coarse-silty, carbonatic, mesic Typic Haploxerolls]) at three rates (10, 20, and 40 mg P kg⁻¹) and incubated for a total of 18 wk with subsamples taken at 2, 5, 9, and 18 wk. Soil samples were analyzed for inorganic and organic NaHCO₃ (Olsen) extractable P and select soils were analyzed at 0 and 12 wk by ³¹P nuclear magnetic resonance spectroscopy (NMR) for soil P characterization. The percentage of WEP and PA (of total P) in the manures were linearly related (r² = 0.94). Increases in Olsen P over time were positively related to the percentage of monoester P in the treatments. At 2 wk, there was a strong negative correlation between the amount of PA added in the treatments and increases in Olsen P. However, by 18 wk, Olsen P was more closely related to the amount of C or N added with the treatments. Changes in PA content of manures due to dietary modification may influence P sorption on calcareous soils in the short-term while other characteristics such as C/P ratio may exert a stronger influence over changes in soil test P over longer time periods.