Caucasian clover (Trifolium ambiguum) specific rhizobia persist in low and high fertility soils in the South Island of New Zealand

Hexaploid Caucasian clover was grown in soil sampled at three New Zealand South Island high country sites to which specific rhizobium inoculum had been added with sowing of the legume in 1975, 1992 and 1997; two sites on the Lincoln University farm sown with inoculated Caucasian clover in 2012 and 2013; and six sites not sown with the crop. Caucasian clover nodulated in soil from all sites sown with inoculated Caucasian clover but did not nodulate in soils from the other sites. Rhizobial isolates from plants in each soil where nodulation occurred showed the same genetic profile, and gave a similar increase in growth of Caucasian clover in low nitrogen soil, as the recommended inoculum for hexaploid Caucasian clover. Caucasian clover specific rhizobia can persist and retain their effectiveness for at least 42 years in New Zealand South Island low fertility, high country soils and 5 years in high fertility soils.