Phytate in Runoff From Surface Applied Animal Manures

Phytate is a common form of organic phosphorus (P) in animal manure, but direct measurement of phytate in runoff has not been previously reported because of difficulty of measuring it in a complex matrix. This study was conducted to measure the contribution of phytate to P loss in runoff using a novel method. Runoff treatments were dairy manure without and with added phytate (DM, DM+ phytate), broiler litter without and with added phytate (BL, BL + phytate), no manure or broiler litter with 2 levels of phytate (phytate-low, phytate-high), and control. Runoff was collected under simulated rainfall and analyzed for total and dissolved reactive P (DRP). Runoff was also separated into sediment (>0.45 mu m) and liquid (<0.45 mu m) fractions for phytate analysis by high-performance ion chromatography. The new method described herein for phytate analysis recovered 70% of phytate spiked into runoff samples. Phytate was found only in the sediment fraction of runoff and was not detected in the liquid fraction, even after concentration by lyophilization. This agreed with an adsorption study, which showed strong adsorption of phytate to soil. Phytate had no effect on DRP in runoff for any treatment, indicating no net inorganic P was released through competitive binding. The majority of P lost in runoff was in forms other than DRP and sediment bound phytate. Existing efforts to control the erosive loss of soil during rainfall events still appear to be the best way to reduce total P loss, irrespective of the presence of phytate.