Manoj K. Shukla

　　Plant and Environmental Sciences, New Mexico State University

　　Las Cruces, NM, USA

　　Soil organic carbon (SOC) plays an important role in assessment and modeling of global climate change. It is also an important factor related to soil quality and productivity. The total C in the soil is almost three times greater than that in the atmosphere and about 240 times greater than that produced by fossil fuel emissions. However, soil C concentrations or stocks are highly spatially and temporally variable, and are functions of land use and management practices. Drastic disturbances such as surface mining, tillage, irrigation practice, and erosion can drastically change the SOC dynamics from aggregate to the watershed scales and have profound influence on the SOC sequestration at small to large scales. The objective of the presentation is to summarize the effects of various land use and management practices on spatial and temporal SOC dynamics at different scales. Soil erosion moved light fraction SOC along with runoff and caused SOC deposition at the foot or toe slope of the fields. Analysis of the macro and micro aggregates as well as the bulk soils showed that more SOC was found at the toe slope or depositional area than summit slope. The data from notillagefield showed an increase of SOC concentrations near the surface but regular tillage showeda decrease. However, considering soil depths upto or greater than 50 cm, total SOC concentrations and stocks werefound to be similar.Application of manure further increased SOC stocks at shallow depths. The rate of increase of SOC stocks from some notill fields was0.61 Mg ha^-1 y^-1at 0-10 cm depth. In contrast, the surface mining drastically decreased the SOC concentration but after reclamation SOC stocks in some Ohiominesoils increased at a rate of 1.86 Mg ha^-1 y^-1at 0-15 cm depth and by 35 years since reclamation, the SOC concentrations and stocks were greater than those of the undisturbed (premined) soil. Overall, these studies showed that SOC stocks at shallow depth increased with duration since disturbance. However, greater increases in SOC stocks were obtained by reclaiming drastically disturbed soils.Properly done soil reclamation has a much higher potential of increasing the SOC sequestration in minesoils.