The use of acetylene reduction to study the effect of nitrogen fertiliser and defoliation on nitrogen fixation by field‐grown white clover

The rate of nitrogen fixation (measured by determining the rate of acetylene reduction) by roots of established white clover which had received 801b/ac of N was 23–30% of the rate for roots from plants which received no fertiliser nitrogen. The rate of acetylene reduction started to decrease within 24 hr of defoliation of the plants and stayed at a low level until the sixth day, after which it increased, reaching levels similar to those of undefoliated plants in 21 days. There was no significant difference in the rate of acetylene reduction between the defoliated and undefoliated plants 34 days after defoliation.