Phosphorus leaching from manure-impacted soils affected by fluctuating water tables
by Jaime Mejias-Bassaletti, Ph.D.
Washington State University
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
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
School:Washington State University
School Location:USA - Washington
Source Type:Master's Thesis
Keywords:soils phosphorus in agriculture
Date of Publication: