Phosphorus leaching from manure-impacted soils affected by fluctuating water tables

by 1969- Mejias-Bassaletti, Jaime

by Jaime Mejias-Bassaletti, Ph.D. Washington State University August, 2005 Chair: Claudio Stöckle The main objectives of this dissertation were: 1. Acquire relevant field data to determine the role of iron reduction in P transport in tile effluents. 2. Explore the relation of the soil redox potential to P release and transport in column studies under dynamic conditions. 3. Develop a P leaching indicator based on the estimate of the P sorption strength in highly P-impacted soils. In the first study, we observed a significant positive correlation between P and Fe2+ concentrations in drainage water from the pasture, but not in that from the corn field. In the latter, a significant relation was found between P Fe3+ concentration. Phosphorus and Fe2+ were positively correlated to drain flow rate in the pasture system v and the same was true for P and Fe3+ in the corn field. In the second study, we demonstrated that an initially oxidized system saturated with P and under dynamic flow conditions can mobilize P after reductive dissolution of ferric iron. These results revealed that a reduced system presents a sink for P due to precipitation reactions but the system turns unstable after the redox potential increases, fixing less P than the oxidized control system. These findings suggest that alternating anoxic-oxic conditions play an important role in subsurface P transport. In the third study, we demonstrated that the inverse of the equilibrium P concentration at zero sorption (1/ce) is a valid estimate of the soil sorption strength, which may be used as an indicator for P leaching potential. Below a threshold level of 1/ce=0.71 L/mg, desorbability parameters increased significantly. vi