Submitted to: Renewable Agriculture and Food Systems
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/22/2005
Publication Date: 3/1/2006
Citation: Liebig, M.A., Carpenter-Boggs, L., Johnson, J.M., Wright, S.E., Barbour, N.W. 2006. Cropping system effects on soil biological characteristics in the Great Plains. Renewable Agric. Food Systems 20(1):36-48.
Interpretive Summary: Understanding biological contributions to soil function is important when assessing soil quality. A multi-location study in the Great Plains was conducted from 1999 to 2002 to evaluate the effect of contrasting cropping systems on soil biological properties over time. The cropping systems (alternative and conventional) differed in the type or frequency of tillage, frequency of cropping, and/or crop rotation diversity. Alternative cropping systems - characterized by continuous cropping, diverse crop sequences, and/or reduced tillage ' had higher levels of microbial biomass and potentially mineralizable N at most locations, indicating these systems had a greater capacity to supply N to plants over the growing season. Alternative cropping systems at four locations also had greater wet aggregate stability than conventional cropping systems, thereby conferring improved air and water movement through the soil in these systems. The composition of the soil microbial community differed considerably across locations, but size of the microbial community was found to be greater in alternative cropping systems at four locations. Preliminary findings from this study indicate there is merit in pursuing alternative management practices to enhance biological indicators of soil quality.
Technical Abstract: Soil biological quality can impact key soil functions. The objective of this study was to determine the effects of management and time on soil biological parameters in contrasting cropping systems across the Great Plains. The cropping systems, which were part of eight long-term experiments, differed in management intensity with respect to type or frequency of tillage, cropping intensity, and/or crop rotation diversity. Soil biological parameters were assessed at depths of 0 to 7.5, 7.5 to 15, and 15 to 30 cm from 1999 to 2002 up to three times per year. Alternative cropping systems (ALT) ' characterized by continuous cropping, diverse crop sequences, and/or reduced tillage ' had greater microbial biomass and potentially mineralizable N (PMN) than conventional cropping systems (CON). Alternative cropping systems at four locations had greater water stable aggregates (WSA) than CON cropping systems in the surface 7.5 cm. Total glomalin (TG), however, differed only at one location (Mandan), where the ALT cropping system had 27% more TG than the CON cropping system. Changes in PMN, WSA, and TG over time tended to fluctuate with changing weather conditions as well as the presence/absence of fallow and/or legume in rotation. Fatty acid methyl ester (FAME) profiles were highly dependent on location. However, alternative cropping systems tended to have greater total extracted FAME, indicating a more abundant soil biomass. Overall, results from this study indicate ALT cropping systems enhanced biological indicators of soil quality.