1995 Volume 41 Issue 1 Pages 67-70
A method for determining nitrogen fixation activity of white clover in the field was examined, and seasonal variations of the activity were studied by acetylene reduction assay in a white clover-orchardgrass grassland with various rates of the mixing. The incubation for acetylene reduction assay was conducted in a transparent plastic chamber settled on an upper guard of a steel tube drived into the ground. All assays were carried out in 10% (v/v) acetylene concentration in air and for 30 min of a incubation time. The injection of acetylene gas and the collecting gas-sample were achieved using syringes through rubber-sealed ports of incubation chamber. The results suggest that this system is useful with some confidence for measuring nitrogen fixation activity of grassland under field condition. The acetylen reduction activity of white clover in the field appeared at the times except snowfall and seasonally changed with two peaks ; a large peak in late May and a small peak in late September except for the temporary fluctuations owing to harvesting and fertilizing. The grassland over 70% in coverage of whiteclover showed nearly the similar quantity of acetylene reduction activity as pure stand of white clover. In mixed stand, the acetylene reduction activity of white clover was promoted by accompanying with orchardgrass unless light condition on leaflets of white clover was deteriolated.
