Soybeans (Glycine max (L.) Merrill), inoculated with 1.75 kg/ha of seed-applied inoculant (Rhizobium japonicum (Kirchner) Buchanan) or 40 kg/ha of granular, soil-applied inoculant, were grown in 1976 and 1977, along with uninoculated control plots, in fields planted to soybeans for the first time. Control plots averaged 2.1 t/ha, compared to 2.6 t/ha for the seed-applied inoculant and 3.1 t/ha for the granular inoculant treatment. However, neither inoculant treatment increased yields over the uninoculated controls on land where soybeans had been grown before. In 1978, two commercial granular inoculants and one seed-applied inoculant were treated at various rates at three sites on new soybean land. Granular inoculants caused consistently higher yields than the seed-applied inoculant. Seed yields increased linearly with rates of granular inoculant which were 1/4, 1/2, 3/4 and 1 times the manufacturers’ recommended rates for soybeans grown in 18-cm rows. However, above the lowest rate, the value of the added yield was only equal to the cost of the extra inoculant. Thus, in the narrow-row soybean cultural system necessary to maximize yields in short-season areas, the manufacturers’ recommended rates of granular inoculant were higher than necessary for maximum economic return.
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MULDOON et al. (1980) studied this question.