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Soil microbiological properties in crop management practices and systems in the Northern Great Plains of North America.

Lupwayi, N.Z. and Burr, M.D. (2010). "Soil microbiological properties in crop management practices and systems in the Northern Great Plains of North America.", in Malhi, S.S., Gan, Y., Schoenau, J.J., Lemke, R.L. and Liebig, M.A. (eds.) - Recent Trends in Soil Science and Agronomy Research in the Northern Great Plains of North America, Research Signpost, Trivandrum, India, Chapter 5, pp. 109-127.

Abstract

Soil microorganisms mediate many important processes for sustainable agriculture. The impacts of crop management practices and systems used in Northern Great Plains on soil microbiological properties were reviewed. Compared to conventional tillage, reduced tillage has generally increased microbial biomass C (MBC), culturable populations and microbial diversity, and decreased CO2 flux. Crop rotations have generally had less effect on microbial biomass than tillage. When tillage and rotation interactions are combined, MBC has been greater in no till rotations that include legumes than in conventionally tilled fallow-wheat systems. Animal manures, green manure containing legumes, and other organic residues have generally increased MBC. Inorganic fertilizers seem to have negative direct effects on soil microorganisms through osmotic effects, and positive indirect effects through enhancement of crop growth, which increases root exudation and crop residues. Herbicides applied at recommended rates have had little effect on soil microbial biomass or respiration. In one study, herbicide applications caused a shift in the microbial community structure without affecting microbial biomass or diversity. Effects of genetically modified crops on soil microbial dynamics have been minor, inconsistent and transient. The small amount of data comparing organic and conventional farms in the Northern Great Plains suggest that soils on organic farms have higher microbial enzyme activity, higher MBC, higher soil organic C (SOC), and a higher ratio of MBC to SOC. Molecular methods have rarely been used in these studies, and it is recommended that such methods be employed to study the diversity of specific functional genes rather than whole microbial community profiles.

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