Farmers occasionally put land into peanut (Arachis hypogaea L.) production that has not been cropped with peanuts in recent history. These fields are generally sparsely populated, if at all, by peanut rhizobia and may be responsive to application of effective peanut inoculant. To field test the need for inoculants, 13 experiments were conducted during 1980-1982 on β€œnew” land on farms in the peanut producing region of southeastern Alabama. Treatments were (1) uninoculated control, (2) granular inoculant applied in-furrow at 3X recommended rate, and (3) ammonium nitrate at 56 kg/ha of N at planting. In 1980, an additional 56 kg N was applied at early bloom. The soil was sampled prior to treatment and numbers of rhizobia capable of nodulating peanuts determined by the most probable number (MPN) procedure. Numbers ranged from nil to 1600 rhizobia per g of soil. Although the soil at six locations contained fewer than 20 rhizobia per g, no yield responses to applied inoculant were obtained. Vine growth, leaf color, and nitrogen content of leaves were unaffected by inoculant. The inoculant provided 1 million rhizobia per seed, which is considered abundant. Lack of any yield responses to fertilizer nitrogen during the 3-year study indicated nitrogen sufficiency in the peanut plants, derived through nodulation and nitrogen fixation by native soil rhizobia. While peanut was not a host legume for these rhizobia during the years prior to these experiments, the rhizobia apparently persisted on alternate legume hosts in the cowpea miscellany in numbers adequate for effective inoculation of peanuts.

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Author notes

1Contribution of the Department of Agronomy and Soils, Alabama Agricultural Experiment Station, Auburn University, AL 36849.