Microbial diversity in the rhizosphere of corn grown under conventional and low-input systems

Microbial processes within the rhizosphere of crop plants are crucial to agriculture. The relation of soil microbial community diversity to cropping system, yield, and soil quality are unclear at present. The Farming Systems Trial at the Rodale Institute Research Center, Kutztown, PA, is a 15-year study in which a conventional corn-soybean rotation has been compared with low-input systems (i.e. animal manure or legumes as nitrogen sources). The effects of the cropping systems on diversity of fast-growing, aerobic, culturable bacteria and fungi were conducted in 1994 by taking 84 cores in between corn plants in June, July, and August. Rhizosphere bacteria and fungi were extracted, plated, and counted. Approximately 6000 bacteria were identified by fatty acid methyl ester analysis, while 18000 fungi were identified by microscopic examination of spores. Microbial diversity and evenness were calculated using several different methods. Total counts, diversity, and evenness were not significantly different for the three cropping systems. These results suggest that conventional agricultural practices may maintain high indices of microbial diversity in the rhizosphere. The functional significance of this needs to be investigated.