Soil microbial diversity and community structure under wheat as influenced by tillage and crop rotation

Soil microbial diversity is important to sustainable agriculture because microbes mediate many processes that support agricultural production. The BIOLOG™ system for detection of specific patterns of substrate utilization by bacteria was used to investigate the effects of tillage 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 phase of different cropping rotations which had been established under zero tillage or conventional tillage on a Gray Luvisol in northern Alberta. Soil was collected from bulk soil at planting time and from bulk soil and wheat rhizosphere at flag-leaf stage of wheat growth. Tillage significantly (P<0.05) reduced the diversity of bacteria by reducing both substrate richness and evenness. The influence of tillage on microbial diversity was more prominent at the flag-leaf stage than at planting time and more prominent in bulk soil than in the rhizosphere at the flag-leaf stage. Microbial diversity was significantly higher under wheat preceded by red clover green manure or field peas than under wheat following wheat (continuous wheat) or summer fallow. The substrate utilization patterns of the bacterial communities also revealed that the bacterial community assemblages under conventional tillage had more similar structures than those under zero tillage. These results indicate that conservation tillage and legume-based crop rotations support diversity of soil microbial communities and may affect the sustainability of agricultural ecosystems.