Saturday, 15 July 2006

Reducing Phosphorus Movement from Soil Contaminated by Over Addition of Manure.

L. Darrell Norton, S. J. Livingston, A. I. Mamedov, and C. Huang. USDA-ARS National Soil Erosion Research Laboratory, 275 South Russell Street,, West Lafayette, IN 47907-2077

This study was conducted to attempt to reduce the potential of polluted runoff from a soil that had received long-term additions of secondary lagoon effluent from a poultry operation through the use of organic waste and gypsum as amendments. The soil studied was a Zulch clay loam (thermic, Udertic Paleusalf), with the clay fraction primarily composed of smectite from Kerten Texas. The soil had received irrigation with effluent from a secondary lagoon to the extent the topsoil contained more than 1200 mg kg-1 Soil Test Phosphorous (STP). The site exceeded the local regulations for STP by several times and would be forced to close if a system to control the runoff potential could not be implemented. Researchers were asked by the land owner to find a feasible method to reduce the potential of eutrophying runoff. The objective of the study presented here was to explore the viability of controlling P in runoff through the use of soil amendments to reduce runoff volume. This was a companion study to another that attempted to sequester P in plants that are harvested and removed from the site as hay. Using a programmable rainfall simulator runoff and soil loss from the contaminated site with treatments consisting of gypsum (1-2.4 Mg ha-1 surface application, GP) a recycled paper product (2.4 Mg ha-1 incorporated+gypsum, PIG), and a control were measured. Plots, 1m wide by 6 m long with <5% slope were subjected to a target rate of 64mm hr-1 rain with an energy of 2.6 kJ m2 for one hour following initial runoff or until steady state runoff was reached. After runoff initiation, runoff and soil loss were measured at 5 minute intervals. Each treatment was replicated four times using water of conductivity <0.018dS m-1. Effectiveness of treatments was related to the surface stabilization of the weakly aggregated smectitic clay loam soil. Generally runoff and soil loss (i) were significantly greater (>2 times) in the disturbed plots than for the undisturbed or virgin plots; and (ii) decreased with the order of control > GP > PIG. The amendments were effective in reducing the degree of surface sealing, i.e. aggregate breakdown, compaction and/or physico-chemical dispersion which occurred more on the disturbed soil, therefore, significantly reducing total runoff or sediment, as well as P loss (>2-4 times). Surface condition showed the dual effect on runoff generation and nutrient loss. Similar to sediment rate, the concentration of Total P (TP) was the greatest in control and the lowest in PG treatments, for both surface conditions, being lesser for undisturbed soil. However, the concentration of Dissolved Reactive P (DRP) in runoff was notably greater from the undisturbed soils at lower runoff amounts due to high concentration of P in the upper surface. The undisturbed soils (for all treatments) had a relative high stability of surface soil aggregates, containing more mobile P in soil solution and runoff could easily entrain DRP from soil before developing a seal. This condition also had a low amount of detached and transported particles with attached P. For the disturbed and sealed soil surface condition with lower porosity and high runoff rate, loading of DRP from the sealed layer was limited and as a result the concentration of TP was a function of only the erosion rate. Across both conditions (disturbed and undisturbed), GP alone was more effective on lowering the concentration of DRP, whereas, PIG treatment was effective in reducing both DRP and TP. The PIG treatment besides chemical flocculation of dispersed clay particles, also increased aggregate stability and drainable porosity of soil surface and decreased the concentration of P in both forms. Decreasing the P loss beside surface condition may also be due to conversion of desorbable soil P to less soluble Ca-bound pools by GP. The use of either GP or PIG in addition to disturbance of the soil the surface appears to be a very effective means of reducing the eutrophic potential of such a contaminated site. The choice between GP alone and PIG will depend on the economics of the situation.

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