Evaluation of Soil Processing Conditions on Mineralizable C and N across a Textural Gradient.

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]