Submitted to: Soil Science Society of America Journal
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/24/2006
Publication Date: 6/21/2006
Citation: Blanco-Canqui, H., Lal, R., Post, W.M., Izaurralde, R.C., Shipitalo, M.J. 2006. Organic carbon influences on soil particle density and rheological properties. Soil Science Society of America Journal. 70:1407-1414. Interpretive Summary: Soil particle density, the density of the solid fraction of the soil, is a fundamental soil property that is used in the calculation of a number of other soil physical properties. Oftentimes, however, soil particle density is not measured but is assumed to be a constant, standard, value for most mineral soils. In this study, we measured soil particle density for one soil type under a variety of soil management practices to determine if these practices affected this parameter and the potential effect of this error on properties derived using particle density. We found that no-till crop management decreased soil particle density compared to moldboard plowing because of an increase in soil organic matter. This effect was particularly large when manure was added to the soil. Under these circumstances if the standard value of particle density is used to calculate soil porosity then it is overestimated by 12%. This suggests that measurement of particle density should be included in routine tests of soil physical properties because they can be strongly affected by management-induced changes in concentration of soil organic carbon. More accurate assessment of how management practices affect soil physical properties will result in the development and recommendation of better management practices for farmers to conserve soil and improve soil quality.
Technical Abstract: Soil particle density (ps) is not routinely measured and is often assumed to range between 2.60 and 2.70 Mg/cubic meter or constant (2.65 Mg/cubic meter) when estimating essential properties such as porosity, and volumetric water and air relations. Values of ps for the same soil may, however, differ significantly from the standard range due to management-induced changes in soil organic carbon (SOC) concentration. We quantified the ps and soil consistency of a Rayne silt loam (fine-loamy, mixed, active, mesic Typic Hapludults) for five long-term (>22 yr) management treatments implemented on adjacent watersheds including moldboard plowed continuous corn (MP), no-till continuous corn (NT), no-till continuous corn with beef cattle manure (NTm), pasture, and forest systems. The impact of measured differences in ps on soil porosity was also assessed. The ps, SOC concentration, bulk density (pb), and Atterberg limits were determined for the 0- to 30-cm soil depth. Management had a significant effect on all properties studied. Mean ps across NT, NTm, and pasture (2.35 Mg/cubic meter) was about 7% lower than that (2.52 Mg/cubic meter) for MP in the 0- to 10-cm depth (P<0.01). The ps was the lowest (2.33 Mg/cubic meter) for NTm within the agricultural practices, while forest had the lowest ps of all land uses (1.79 Mg/cubic meter). The NTm caused a reduction in ps and pb and an increase in SOC concentration, liquid limit (LL), plastic limit (PL), and plasticity index (PI) more than NT. Surface soils under MP had the highest ps and pb and the lowest SOC concentration, LL, PL, and PI (P<0.01). The SOC concentration was correlated negatively with ps (r squared = 0.75) and positively with Atterberg limits (r squared = 0.64) at > 20-cm depth (P<0.01). Estimates of soil porosity for NT, NTm, and pasture using the constant ps overestimated the "true" porosity by 12% relative to that using the measured ps (P<0.01). Overall, ps and soil consistency were sensitive to management-induced changes in SOC concentration, particularly in NTm, and that reduction in ps reduced estimates of soil porosity.