SOIL MICROBIAL DIVERSITY AND COMMUNITY STRUCTURE UNDER WHEAT AS INFLUENCED BY TILLAGE AND CROP-ROTATION

Soil microbial diversity is important to sustainable agriculture becau se microbes mediate many processes that support agricultural productio n. The BIOLOG(TM) system for detection of specific patterns of substra te utilization by bacteria was used to investigate the effects of till age and crop rotation on the diversity and community structure of soil bacteria. In each of 2 yr, soil was sampled (0-7.5 cm) in the wheat p hase of different cropping rotations which had been established under zero tillage or conventional tillage on a Gray Luvisol in northern Alb erta. Soil was collected from bulk soil at planting time and from bulk soil and wheat rhizosphere at flag-leaf stage of wheat growth. Tillag e significantly (P < 0.05) reduced the diversity of bacteria by reduci ng both substrate richness and evenness. The influence of tillage on m icrobial diversity was more prominent at the Hag-leaf stage than at pl anting time and more prominent in bulk soil than in the rhizosphere at the flag-leaf stage. Microbial diversity was significantly higher und er wheat preceded by red clover green manure or field peas than under wheat following wheat (continuous wheat) or summer fallow. The substra te utilization patterns of the bacterial communities also revealed tha t the bacterial community assemblages under conventional tillage had m ore similar structures than those under zero tillage. These results in dicate that conservation tillage and legume-based crop rotations suppo rt diversity of soil microbial communities and may affect the sustaina bility of agricultural ecosystems. Crown copyright (C) 1998 Published by Elsevier Science Ltd. All rights reserved.