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Soil biological activity is an important component of a well-functioning soil. Methodologies for estimating this process vary due to a variety of theoretical, functional, and expediency considerations. We tested the effects of soil processing (sieve size), water delivery method (from top and from capillary), and soil organic matter content (two levels based on depth of sampling) on mineralizable C and N during 0 to 1, 0 to 3, and 0 to 24 d of incubation from soils ranging in texture. Mineralizable C was not affected by sieve size, suggesting that fine grinding should not affect results. Water delivery method did affect mineralizable C estimates at 0 to 1 and 0 to 3 d of incubation, as water delivered by capillary allowed soil to absorb to 70 ± 5% water-filled pore space compared with controlled delivery to 50% water-filled pore space from the top. The extra water only hindered mineralizable C in soils with coarse texture (i.e., sandy loam), whereas mineralizable C in other soil textures was not affected. Net N mineralization during 24 d of incubation was negatively impacted by the higher water content, independent of soil texture, but more so when soils high in organic matter were sieved coarsely than when sieved finely. Despite these variations, close association occurred between mineralizable C (0 to 1 and 0 to 3 d) and net N mineralization (0 to 24 d at 50% water-filled pore space), suggesting that length of incubation and method of water delivery should not restrict the choice of methodological variation from those used here to assess soil biological activity. However, a standard methodology has become increasingly necessary to compare absolute values across management systems, farm types, and regions. [ABSTRACT FROM AUTHOR]

Prediction of soil organic C sequestration with adoption of various conservation agricultural management approaches is needed to meet the emerging market for environmental services provided by agricultural land stewardship. The soil conditioning index (SCI) is a relatively simple model used by the USDA-Natural Resources Conservation Service to predict qualitative changes in soil organic matter. Our objective was to develop a quantitative relationship between soil organic C derived from published field studies in the southeastern USA and SCI scores predicted from matching management conditions. We found that soil organic C sequestration (at 20 ± 5 cm depth) could be reliably related to SCI across a diversity of studies in the region using the regression slope: 1.65 Mg C ha SCI [which translated into a rate of 0.25 ± 0.04 Mg C ha yr SCI (mean±standard error of 31 slope estimates)]. The calibration of soil organic C on SCI scores will allow SCI to become a quantitative tool for natural resource professionals to predict soil organic C sequestration for farmers wanting to adopt conservation practices. [ABSTRACT FROM AUTHOR]