White clover seed inoculation and coating in New Zealand

Abstract

This paper reviews the requirement for inoculation of white clover (Trifolium repens) seed with rhizobia bacteria in New Zealand. The pastoral industry relies on the nitrogen fixed by clover's rhizobia bacteria. These rhizobia were not present in soils prior to European settlement, but were introduced as contaminants, and naturally spread with pastoral development. The advent of large scale land development in the 1950s identified areas where clovers failed to nodulate and establish due to the absence of rhizobia, which led to the development of inoculated lime coated seed. Rhizobia have spread widely throughout New Zealand, and in the great majority of situations where pasture is being sown, soils now contain high levels of resident rhizobia capable of nodulating white, red and alsike clover, and inoculation of clover seed is not required. However, it is suggested the use of inoculated clover seed should be considered in the following three situations as an insurance against nodulation failure: undeveloped grasslands with no evidence of resident clover; virgin pastoral land cleared directly from scrub; and paddocks cropped with maize continually for over 10 years. It has been hypothesised that inoculating clover seed may improve clover growth through introducing more effective rhizobia with better nitrogen fixation ability, but the research in this area suggests there is little likelihood of any significant response from doing this. Keywords: rhizobia, inoculation, coated seed, white clover, red clover, alsike clover