Submitted to: Precision Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/15/2004
Publication Date: 2/15/2004
Citation: Johnson, C.J., Drijber, R.A., Wienhold, B.J., Wright, S.E., Doran, J.W. 2004. Linking microbial-scale findings to farm-scale outcomes. Journal Precision Agriculture 5:311-328. Interpretive Summary: Farm management affects the type, number, and activity of microscopic organisms in soil; these organisms, in turn, impact soil physical structure and suitability for plant growth, nutrient availability to the crop, and crop yields. In order to evaluate the economic and environmental impacts of different management approaches across various soil types, farmers and researchers must be able to link information collected from the microscopic level on up to physical and chemical soil tests, field-level yield monitor maps of crop yield, and whole-farm economics. An on-farm farm-scale experiment (610 ac) in semiarid northeastern CO was mapped for electrical conductivity (EC) using a commercially available EC meter. Low, medium low, medium high and high zones (ranges) of EC were evaluated as a basis for comparing data collected at these different scales. Microscopic measurements of specific soil organisms, chemical and physical tests indicative of productivity, and wheat yields (where wheat follows a fallow year) were different among EC zones, increasing as EC decreased. These results indicate that zones of EC can be used relate management- induced changes in soil and crop productivity. By measuring these changes and farm profitability, over time, management practices can be identified that maximize farm profits while minimizing negative effects such as soil erosion, leaching and runoff, acidification, and compaction.
Technical Abstract: A farm-scale experiment (250 ha) was established in 1999 to monitor yield, economic, and soil ecological response to conversion from conventionally-tilled winter wheat (Triticum aestivum L.)-fallow to a no-till winter wheat-corn (Zea Mays L.)-proso millet (Panicum miliaceum L.)-fallow rotation. The site was mapped and separated into four zones (ranges) of ECa from which 96 soil samples were collected and analyzed for physical, chemical, and biological properties (0-7.5 and 0-30 cm depths). Vesicular-arbuscular mycorrhizal (VAM) fungi were evaluated in 1-2 mm soil-aggregate fractions (0-7.5 cm depth) using C16:1(cis)11 fatty acid methyl ester biomarker (C16vam), glomalin immunoassay, and wet aggregate stability (WAS) techniques. Wheat yields were mapped using a geo-referenced yield monitor. Measurements of C16vam and WAS increased among cropping treatments as: fallow<wheat<corn<millet. Glomalin concentrations were different among ECa zones (P=0.01) across crop and replicate treatments, while WAS and C16vam were delineated by ECa within fallow treatments (confounding effect of crop removed). All VAM measures were negatively correlated with ECa. Within-field ECa classification delineates: (1) measures of VAM presence and activity, (2) soil physical and chemical properties related to production potential, and (3) wheat yields, providing a point of reference through which data collected at different levels of scale can be related.