The Influence of Irrigation and Rhizobium japonicum Strains on Yields of Soybeans Grown in a Lakeland Sand1

Abstract

AbstractUnder existing management technology, Lakeland sands (Typic Quartzipsamments) produce low yields of soybeans [Glycine max (L.)Merr.] in North Carolina. These soils have an available water holding capacity of only 4.0% on a weight basis and as a result require about 2.5 cm of water every 5 to 6 days during the growing season to produce acceptable crop yields. In addition, Lakeland sands usually have extremely low or a totally nonexistent indigenous population of Rhizobium japonicum. Information on irrigation and nodulation effects is needed to make these soils more productive.The objectives of this study were to investigate the influence of irrigation and inoculation with different R. japonicum strains on yields of soybeans grown in a Lakeland sand. The study was conducted at the Sandhills Research Station at Jackson Springs, North Carolina. Additional nonirrigated plots inoculated with strains 31, 110, and 122 were initiated on finer textured North Carolina soils for comparative purposes to the Lakeland sand.Soil moisture treatments included plots not irrigated and plots irrigated each week with 2.5 cm of water. The five inoculation treatments consisted of a set of noninoculated plots and plots inoculated with strains of R. japonicum representing serogroups 31, 76, 110, and 122 at the rate of 50 ✕ 104 cells per cm of soybean row. Numbers of soil rhizobia were monitored throughout the study using a plant infection and MPN technique.Irrigated soybean seed yields were significantly greater when inoculated with rhizobia of either serogroup 110 or 122 than yields from noninoculated but irrigated plots. Inoculation without irrigation did not increase soybean yields. It was also observed that inoculated, irrigated soybeans had greater nodule mass and numbers of nodules than the nonirrigated and/or noninoculated plots. All four serogroups used in the study adequately nodulated soybean roots under irrigation and produced fewer nodules on soybean roots in the nonirrigated plots. On the basis of seed yield, strain ranking from best to worst was: 122>110>31>76. The noninoculated controls yielded higher than serogroup 76 but less than those soybeans in plots inoculated with serogroup isolate 31.