Fertilizer and Lime Research Centre, Massey University
Abstract
In New Zealand, nitrate (NO₃⁻) leaching is a major environmental problem associated with intensive agriculture. Research suggests that plants with deeper roots and high evapotranspiration rates, such as poplars (Populus) and willows (Salix), may reduce NO3- leaching. In New Zealand, willows and poplars have largely been studied in relation to their soil conservation benefits, use as stock fodder, biomass production and phytoremediation of contaminated soil. This review compiles information on the use of poplars and willows in agricultural systems and explores their potential application to the management of NO₃⁻ leaching. Studies show reduced NO₃⁻ leaching under short rotation coppice willows. However, the establishment and harvesting phases are risk periods for NO₃⁻leaching where nitrogen application should be avoided. A case study has identified a potential for role of poplar and willow silvopastoral systems on intensively-managed irrigated farms of the Canterbury Plains. Height restrictions due to overhead irrigation, stock fodder value and the need to restrict light competition with pastures suggest Salix viminalis (with annual coppicing) is the most suitable species for integration into these farms. Further research is needed to quantify both the possible reduction in N losses and the additional on and off-farm benefits of poplar and willow silvopastoralism in the context of intensive farming in New Zealand
