Land application of liquid waste: a case study of piggery waste application on light soils
Abstract
This study was conducted on soil from the Burnham piggery which is located on the Alluvial plains of mid-Canterbury between the Waimakariri and Selwyn rivers. Effluent from the piggery is spray-irrigated onto the adjacent land. Soils at the disposal sites are flat, somewhat excessively drained. Subsurface drainage of effluent has a measurable impact on the quality of groundwater.
The case study was designed to determine the effects of land application of piggery waste on the contamination of groundwater. The amounts of NO₃⁻-N and NH₄⁺-N leached from small undisturbed soil lysimeters (180 mm dia * 150-200 mm deep) were compared under a standard solution application and a slurry application.
Examination of breakthrough curves from solution experiments indicated extensive preferential flow of solute had occurred through natural soil macropores.
The initial peak recovery of N in the standard solution experiment appeared quickly (after 0.3 pore volume) and about 80% of the N applied was recovered by 1.0 pore volume of drainage.
The rate of recovery then decreased and became constant. Total recovery of N in the leachate equalled approximately 100% following the application of an amount of water equivalent to the amount of rainfall that would occur during an average winter period.
The total mean percent recovery of N in the slurry experiment was fairly evenly distributed and about 35% of the total N in the leachate was recovered by 1.0 pore volume of drainage. The total recovery of N in the leachate equalled about 8% following the application of an amount of water equivalent to the amount of rainfall during an average winter period.
About 76% of applied N was recovered from the soil. Results were also predicted assuming the soil to be at field capacity and permanent wilting point at the time of slurry application and the start of leaching. Cases of maximum rainfall and evapotranspiration, and, minimum rainfall and evapotranspiration over the period were also considered.
