Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/27/2017
Publication Date: 3/22/2018
Citation: Franzluebbers, A.J., Haney, R.L. 2018. Evaluation of soil processing conditions on mineralizable C and N across a textural gradient. Soil Science Society of America Journal. 85:354-361.
Interpretive Summary: Soil testing for biological activity is rapidly becoming more common to assess soil health. Scientists from USDA-ARS in Raleigh NC and Temple TX tested a few soil processing variables that could determine the suitability of different approaches for obtaining robust and reliable estimates of soil biological activity. How finely the soil was ground did not have a large impact on soil-test results, but method of water delivery did in coarsely textured soils. Incubating soil for 3 days produced larger values with somewhat less variability than soils incubated for only 1 day. Although water delivery method affected the absolute value of soil biological activity, it did not affect the ability of the soil test to predict nitrogen mineralization (i.e. soil nitrogen availability to plants). These results will be highly valuable to soil scientists and lab managers that promote and conduct soil testing services for agricultural producers.
Technical Abstract: Soil biological activity is an important component of a well-functioning soil. Methodologies for estimating this process in soil 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 base on depth of sampling) on mineralizable C and N during 0-1, 0-3, and 0-24 days 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 0-1 and 0-3 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 still occurred between short-term mineralizable C and net N mineralization during 24 d, suggesting that length of incubation and method of water delivery should not restrict the choice of methodology to assess soil biological activity. However, a standard methodology would be preferred to compare absolute values across management systems, farm types, and regions.