Pasture legumes, like clovers, are the key to the success of New Zealand’s pastoral systems. Nitrogen is maintained by the biological fixation of nitrogen gas from the air by rhizobium bacteria that reside in the root nodules of legumes, to supply nitrates for plant growth. While this theory is still dominant in New Zealand agriculture, nitrogen, particularly in intensive systems such as dairying, can remain deficient with increasing amounts of nitrogen fertilisers applied.
White Clover is often considered the most critical legume for New Zealand agriculture. It is most suited to fertile soils in areas with warm, moist summers or under irrigation. White Clover will stop growing when the temperature is less than 8 degrees and therefore is not very productive during winter, and long periods of summer drought may also limit its growth potential. White Clover has a tap root that rarely survives more than two years. Following this, it develops a small shallow root system from stolon nodes. While it can be susceptible to drought, grass grub, and competition from other pasture species, it has adapted by reproducing both stolons and seeds. The stolons are typically below grazing height, making White Clover tolerant to close intensive grazing.
White Clover is very efficient at fixing nitrogen. A pure stand of White Clover is estimated to fix up to 700kg N/ha/Yr under ideal growing conditions.