|Van Berkum, Peter|
Submitted to: Archives of Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/12/2001
Publication Date: N/A
Interpretive Summary: Globally, soybean is the most important grain legume. Because soybean is a legume it benefits from biological nitrogen fixation through a symbiosis with soil bacteria of two different genera. In agriculture, the benefit is in the form of enhanced efficiency of crop production. Management of biological nitrogen fixation involves the inoculation of the appropriate bacterial cultures at the time of sowing. These bacterial cultures are available to the farmer as inoculants manufactured in industry. The problem is that many different bacteria are available, but comprehensive investigations for genetic differences have not been done and nothing is known about colonization of soils by the bacteria to "create" a native population in American production fields. There are two possibilities, bradyrhizobia of American legumes are able to nodulate soybean or bradyrhizobia can be introduced to soils by human activities other than inoculation of the crop directly. Our program has the objective to study native populations of bradyrhizobia that nodulate soybean. Here we report that a "native" population of soybean-nodulating bradyrhizobia may establish from application of municipal waste. As a result, the introduced bacteria may compete with inoculants of soybean for nodulation of the crop. This potentially could interfere with management of the symbiosis and could lead to reduced crop production efficiency. Our results will be useful to scientists who are interested in the soybean symbiosis and efficiency of soybean production.
Technical Abstract: The interaction of biosolids compost application and its effect on bradyrhizobia in the soil was examined. Seven bradyrhizbial genotypes, among 170 isolates, were recovered from soils receiving either no biosolids application or rates of 73 or 146 Mg/ha for three successive years. From our data we concluded that the diversity of bradyrhizobia that nodulate cowpea and soybean was limited in soils of our experimental site. The distribution of the genotypes of Bradyrhizobium recovered from cowpea nodules appeared to be interrelated with the level of biosolids amendment of the soil, with the exception of one of the genotypes. Two of the bradyrhizobial genotypes that were recovered nodulated both soybean and cowpea. Because soybean-nodulating bradyrhizobia were not recovered from control plots, we concluded that they had been introduced together with the biosolids compost application.