Nitrogen fixation during 1979–81 in 2 pastures on the manawatu plains

Abstract

Nitrogen fixation was monitored by the acetylene reduction assay in 2 pasture types rotationally grazed by dairy bulls. One pasture was an old established sward containing ‘Grasslands Huia’ white clover (Trifolium repens L.) and nonpedigree white clovers and grasses. The other consisted of ‘Grasslands Pitau’ white clover, ‘Grasslands Pawera’ red clover (T. pratense L.), and grasses. Annual N fixation during 1979–81 varied from 76–105 kg N/ha. These are less than half the values previously recorded at this site. Annual clover yields (2.0–2.2 t DM/ha) were similar to those reported earlier, so nitrogen fixation per unit clover grown was low in the present study. This suggests accumulation ofavailable N in the soil since the last survey. Despite an increase in available N, soil total N seems to be declining at this site. © 1983 Taylor & Francis Group, LLC.