Soybean Response to Rhizobium japonicum Strain, Row Orientation, and Irrigation

Stresses or environmental differences associated with soybean [Glycine max (L.) Merr.] row configuration and drought could affect selection and symbiotic performance of Rhizobium japonicum strains and subsequent growth and yield of soybean. The present field studies were conducted in 1981, 1982, and 1983 to assess the response of soybean nodulation, growth, and yield to R. japonicum strains, row orientation, and irrigation. Strains USDA3Ilb110 (110), NC1004 (04), and B587 (587) of R. japonicum were compared to indigenous populations in a Norfolk loamy sand (fine loamy, siliceous, thermic, Typic Paleudult). Soybean cultivars ‘Davis,’ ‘Braxton,’ and ‘Coker 338’ were grown with and without irrigation, with east/west and north/south row orientations, and with inoculation variables. The seasonal weather was different for air temperature, rainfall, and solar radiation; and soil temperatures were generally 1 to 5 °C lower for north/south-oriented than east/west-oriented rows at depths of 5 and 15 cm. Nodular occupancies of inoculated strains were increased by inoculation in 1981 and 1982, but not in 1983. No significant differences in N concentration or total N of soybean shoots were found in any year. Yet, a strain ✕ row orientation interaction occurred for seed yield in all 3 yr, and a strain by irrigation interaction occurred in 1983. Seed yield of soybean inoculated with strain 04 or 110 were significantly different for row orientation; differences ranged from 0.24 to 0.43 Mg ha⁻¹ for irrigated soybean. Soybean inoculated with 587 was not significantly different in seed yield for row orientation. It was concluded that environmental differences induced by row orientation influence some R. juponicum strains in soybean more than others, particularly under irrigated conditions.