Linking microbial-scale findings to farm-scale outcomes in a dryland cropping system
2004
Johnson, C.K. | Wienhold, B.J. | Doran, J.W. | Drijber, R.A. | Wright, S.F.
Soil biological response to management is best evaluated in field-scale experiments within the context of the soil environment and crop; however, cost-effective methods are lacking to relate these data which span multiple spatial scales. We hypothesized that zones of apparent electrical conductivity (ECa) could be used to integrate soil properties (sampling-site scale), microbial-scale measures of vesicular-arbuscular mycorrhizal (VAM) fungi, and field-scale wheat yields from yield maps. An on-farm dryland experiment (~250 ha) was established wherein two (~32-ha) fields were assigned to each phase of a winter wheat (Triticum aestivum L.) - corn (Zea mays L.) - proso millet (Panicum miliaceum L.) - fallow rotation. Each field was mapped and classified into four zones (ranges) of ECa. Soil samples were collected from geo-referenced sites within ECa zones and analyzed for multiple soil properties associated with productivity (0-7.5 and/or 0-30 cm). Additionally, VAM fungi were assessed using C16:1(cis)11 fatty acid methyl ester biomarker (C16vam), glomalin immunoassay, and wet-aggregate stability (WAS) techniques (1-2mm aggregates from 0- to 7.5-cm soil samples). Concentrations of C16vam and WAS increased among cropping treatments as: fallow < wheat < corn < millet. Glomalin across crops and replicates, C16vam and WAS in fallow (crop effect removed), soil properties associated with productivity, and wheat yields were negatively correlated with ECa and different among ECa zones (P < = 0.05). Zones of ECa provide a point of reference for relating data collected at different scales. Monitoring cropping system parameters and profitability, over time, may allow linkage of microbial-scale processes to farm-scale economic and ecological outcomes.
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