Rhizobium inoculant for soybean [Glycine max (L.) Merrill] in Mekong Delta

Summary Rhizobial inoculation trials were conducted in an acid heavy clay soil in Mekong Delta, Viet Nam, using peat based inoculants produced locally and the commercial granular product of Nitragin CCo., Wisconsin, USA. The pH of these soils ranged from 4.5 to 5.1. Two soybean cultivars, MTD₆ and MTD₁₀, were tested as host plants. There were no significant differences between locally made inoculant treated plants and the uninoculated controls in both cultivars. But, the Nitragin inoculation improved all plant characteristics examined in both cultivars. Grain yields of Nitragin inoculated plants of cultivar MTD₆ and cultivar MTD₁₀ were 6.5 and 5.5 times as much as those of the controls; protein content of grain increased 11 and 16 percent, respectively. Well nodulated plants had shorter life cycles, flowering durations, and days to flowering. The Rhizobium symbiosis resulted in an additional 153 kg grain-N/ha. These studies show that a surface coated commercial multistrain inoculant can be used to successfully grow soybeans in the acid, heavy clay soils of the Mekong Delta.