Lucerne establishment studies on uncultivated country

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Abstract
Results are reported of pot and laboratory trials designed to investigate nodulation problems in lucerne found in a previous field trial on dry uncultivated country in North Canterbury dominated by two species of Notodanthonia. In the pot trial, using undisturbed turfs from the field trial site subjected to different sward treatments, good nodulation occurred only where the vegetation had been completely destroyed by dalapon/ amitrole several weeks before sowing. Where vegetation was merely checked with paraquat before sowing, or was still actively growing, few lucerne plants nodulated, and those which did carried small nodules. These results were closely associated with the effects on rhizobia during their incubation' with extracts from the soil beneath the different sward treatments of the pot trial. Rhizobia survived well during incubation where the vegetation had been destroyed completely, but survived poorly where it was only checked or still grew actively. It is concluded that a material antagonistic to Rhizobium meliloti occurs in the soil beneath the resident vegetation of the field trial site. This material appears to prevent good nodulation of oversown lucerne and reduce the size of the few nodules that do form. Since there is a strong possibility that this toxin was a product of danthonia, it is recommended danthonia be completely destroyed several weeks before sowing when introducing lucerne into areas where the vegetation is dominated by this grass.

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