AN INOCULANT RHIZOBIUM STRAIN FOR IMPROVED ESTABLISHMENT AND GROWTH OF HEXAPLOID CAUCASIAN CLOVER (TRIFOLIUM-AMBIGUUM)

Strains of Rhizobium leguminosarum bv. trifolii present in New Zealand soils are ineffective on Caucasian clover (Trifolium ambiguum) and in oculation with an effective strain of rhizobia is essential for nodula tion. However, problems have been encountered with nodulation of overs ewn Caucasian clover and this study was conducted to determine whether nodulation could be improved by the use of an improved strain of rhiz obia. Five strains of rhizobia were compared with a re-isolate (ICC105 ) of the recommended New Zealand commercial inoculant strain (ICMP4073 b) for their effect on the establishment of oversewn hexaploid Caucasi an clover in Canterbury and Otago, South Island, New Zealand. When str ains were incorporated in peat inoculant and used to inoculate seed in a commercial pelleting process, one strain (ICC148) increased the per centage of seedlings nodulated over that obtained with ICC105, from 23 % to 49%. In a further evaluation of these two strains, seed was inocu lated and lime-coated in the laboratory and stored for either 1 or 20 days before oversewing on 7 tussock grassland sites. Inoculation with ICC148 resulted in a 1.3-fold increase in the percentage of seedlings nodulated over that obtained with ICC105. In addition, dry matter (DM) weights of individual seedlings were increased with strain ICC148. Th e dry weights of individual Caucasian clover plants after 6 and 13 mon ths increased 1.5 and 3.0-fold, respectively, when inoculated with str ain ICC148. Inter-tussock Caucasian clover DM after 17 months was 1870 kg ha(-1) for plants inoculated with ICC105 and 3480 kg ha(-1) for pl ants inoculated with ICC148. Foliage N contents in spring were increas ed from 2.6% to 3.1%, when seed was inoculated with ICC148. These resu lts strongly support a change in the Rhizobium strain recommended in N ew Zealand for hexaploid Caucasian clover to strain ICC148.