SOIL POPULATIONS OF RHIZOBIUM-JAPONICUM IN A COTTON CORN SOYBEAN ROTATION

The ability of legume root nodule bacteria to live in soil in the absence of host plants has great practical value. Since soybean left bracket Glycine max (L. ) Merrill right bracket is extensively grown and its value is largely dependent upon effective N//2 fixation, it is important to develop an understanding of the ecology of its nodule bacteria, Rhizobium japonicum. In order to determine seasonal trends in R. japonicum populations in relation to cropping and soil fertility conditions that severely limit crop production, selected treatments in a long-term field experiment were sampled at approximately 30-d intervals over a 2-yr period for R. japonicum numbers in soil of the plow layer. Soil was serially diluted and applied to surface-sterile soybean seed in growth pouches to determine most probable number (MPN). Refs.