Production and nitrogen fixation by #x2018;Grasslands Kopu#x2019; and #x2018;Grasslands Huia#x2019; white clovers under different nitrogen regimes

摘要

The production and nitrogen (N) fixation by established #x2018;Grasslands Kopu#x2019; and #x2018;Grasslands Huia#x2019; white clovers grown with ryegrass were measured in spring 1986 after application of15N-labelled ammonium sulphate at 1, 5, 10, 25, and 50 kg N/ha, to plots with nil or regular N fertiliser use in the past. Application of 25 and 50 kg N/ha produced a large increase in grass growth (18 - 28 kg dry matter (DM)/kg N). However, there was little effect of recent N application on growth or N2fixation by Kopu or Huia white clovers although a maximum was recorded at 5 kg N/ha which was most prominent with Kopu. Past N use reduced growth and N2fixation by about 40070 for both clovers. Kopu and Huia absorbed similar amounts of N from the soil. However, Kopu produced 15 more DM and fixed 35 more N than Huia. It also fixed a significantly greater proportion of its total N from atmospheric N2(84v.79 respectively).