Growth and nitrogen fixation of pure stands of three pasture legumes with high/low phosphate

The growth and N‐fixation capacities of pure stands of white clover ( Trifolium repens L.), suckling clover ( T. dubium Sibth.), and Lotus pedunculatus Cav. were compared under high and low phosphate conditions in mown plots for 3 years. With high inputs of P, white clover yielded 10% more herbage DM and nitrogen than lotus, but with low P input lotus yielded 30% more than white clover. The main factor operating was the greater ability of lotus to take up P from the soil. Full development of an efficient N‐fixing system took a year in lotus, much longer than for white clover. Suckling clover performed better than white clover at low P during its growing season. White clover and lotus accumulated twice as much soil N as suckling clover. Phosphate had no effect on soil N accumulation. The mean annual amount of N fixed (herbage + soil) at high P was 570, 590, and 265 kg/ha, and at low P was 400, 410, and 195 kg/ha for white clover, lotus, and suckling clover respectively.