Crop Rotation Effects on Soil Microbial Populations, Biomass and Diversity under Wheat in a Brown Loam

The inclusion of grain and green manure (GM) or forage legumes in cereal production systems on the Prairies does improve the fertility and quality of soils (Wright 1990; Campbell et al. 1992; Green and Biederbeck 1995; Biederbeck et al. 1998). Legume-based cropping systems can also reduce nitrogen losses and greatly increase the proportion of crop residuecarbon that is sequestered in stable soil organic matter (Drinkwater et al. 1998). As growing environmental and economic concerns are shifting agricultural systems away from high-input to more ecologically sustainable systems (Tilman 1998), there will be increasing reliance on biological soil processes and on high microbial diversity, since soil microorganisms mediate most of the processes that are essential to agricultural productivity (Paul and Clark 1996).