Effluent loading rates for irrigated plantations—a water balance model

Summary

Disposal of municipal and industrial effluents to rivers is a major source of river pollution in Australia. Since an increasingly popular alternative for reducing discharge of nutrients to rivers and promoting wood production, is to use effluents to irrigate tree plantations, there is a strong demand for accurate information on the water and nutrient consumption of effluent-irrigated plantations. Research on growth and water-use of Pinus radiada (D. Don) plantations treated with a wide range of water and nutrient supplements over 4 years has resulted in the development of WATLOAD, an empirical water-balance model of irrigated plantations. The central biological parameter is the amount of foliage carried by the trees, which affects throughfall and stemflow, the transpiration rate of the trees and the evapotranspiration rate of the pasture grass or understorey. The model calculates the monthly amount of effluent that can be applied to a plantation in a given climate from planting to canopy closure with minimal risk of increasing nutrient contamination to waterways. It calculates the area required to treat a given volume of effluent and the amount of winter storage required.