Biological nitrogen fixation and biomass production in the understorey vegetation of an organic apple orchard in Canterbury, New Zealand

Abstract

One of the basic requirements for sustainable management of soils is to ensure that soil fertility is maintained in a productive state and conditions so as to enable the soil to continue to provide viable economic yields with minimum degradation of soil quality and quantity. The practice of supplying nitrogen to fruit trees from biological nitrogen fixation by pasture legumes in the understorey vegetation of orchards is a sustainable means of maintaining soil fertility. Quantitative field measurements of amounts of biological nitrogen fixation and biomass production by three different kinds of understorey vegetation in an organic apple orchard in Canterbury New Zealand was conducted over a period of two years. Results obtained showed that biological nitrogen fixation varied from 118 to 126 kg N ha⁻¹ over the period of two years and herbage production varied from 8 to 12 t ha⁻¹. Nitrogen fixation was significantly correlated with clover dry matter production. Results were affected by seasons and understorey management practices. Implications of these results are discussed with respect to management strategies for enhancing biological nitrogen fixation in organic orchards.