XII. General discussion

Nitrogen relationships are discussed for nine grazing‐trial sites throughout New Zealand. Measured clover growth and N fixation were not necessarily closely related, giving substantial seasonal and annual variation in N fixation per unit clover grown. Other factors, including weather and soil characteristics, influenced the extent to which clovers obtained their nitrogen requirements from fixation or by direct uptake of soil N. Annual N fixation in developed lowland pastures was around 184 kg N/ha — less than half the value previously thought to occur. This lower value was consistent with lower clover yields and higher soil N status than recorded in earlier studies. Annual N turnover in the pastures was large, but showed no simple relationships with either N fixation or soil characteristics. Grass yields were relatively insensitive to climatic variation and not simply related to either clover yields or N fixation.