Nitrogen fixation during improvement of North Island hill country pastures

Abstract Nitrogen (N) fixation was measured, using the acetylene reduction assay, in hill pastures at the Ballantrae Hill Country Research Station near Woodville. Measurements were made over a 12 month period starting in September 1976, on sunny and shady aspects of the six fertiliser × grazing management treatment combinations of a larger grazing trial. Fertiliser treatments were LF (750 kg/ha superphosphate total over the previous 4 years) and HF (1800 kg/ha total plus 1250 kg/ha ground limestone). Grazing managements were set stocking with sheep (SSS), and rotational grazing with sheep (RGS) or cattle (RGC). Annual fixation averaged 103 kg N/ha in LF and 201 kg N/ha in HF pastures, and 105,129 and 224 kg N/ha in SSS, RGS, and RGC pastures respectively. These levels were in contrast to an annual level of 34 kg N/ha measured within the same area 2 years previously, when pasture improvement was much less advanced. Annual N fixation was similar on sunny and shady aspects, but the pattern of seasonal fixati...