The nodulation of annual summer legumes sown on the far north coast of NSW

Abstract

Difficulty has been encountered in securing the nodulation of inoculated annual summer legumes (Dolichos lablab L, and Vigna sinensis (L) Endl, ex Hassk.) sown on the far north coast of New South Wales and using strains that had proved satisfactory in sand culture trials. Satisfactory nodulation by the inoculum strain, when applied at a normal level, was secured in only one of ten trials that involved a clean cultivated seed bed and in one out of eight that were seeded directly into the grass sward. Reduction of grass growth by prior treatment with herbicide did not improve nodulation. Four out of six trials where the inoculum was 10x 100x normal were satisfactorily nodulated by the applied strain; the two failures were associated with dry conditions after sowing. Later sowings (January-March) generally resulted in better nodulation than those in December, but restricted the growing season to too short a period. A more detailed glasshouse trial with a red basaltic soil and which simulated sod-seeding conditions provided a quantitative basis for the relationship between size of inoculum and success in establishment. The extent to which the difficulties encountered in this work are due to the nature of the host, the bacterium, or both, has yet to be more fully investigated, along with the possible influence of factors in the root environment. The results illustrate the importance of field trials in strain selection and recommendations for inoculant use.