EFFECTS OF CULTIVATION AND ABANDONMENT ON SOIL ORGANIC-MATTER IN NORTHEASTERN COLORADO

The influence of climate and soil texture on soil organic matter losses due to cultivation are rarely addressed due to lack of appropriately paired sites. In addition, soil organic matter recovery on previously cultivated fields is not well understood. In this study, we identified seven sites that have native and abandoned fields and five sites that have native, abandoned, and cultivated fields. All sites are in the northeastern Colorado shortgrass steppe, crossing a precipitation range from 320 to 370 mm, and have sand contents from 36 to 67%. Historical cultivation reduced soil C and N across this region by between 16 and 42%. Although variation in native soil C and N at these sites correlates with climate and soil texture, variation among sites in soil losses due to cultivation is not explained by these variables. We used a statistical model and a simulation model to estimate patterns of soil loss across sites; neither model predicted variation among sites adequately (P > 0.05). We suggest that local-scale variability in organic matter losses due to cultivation are strongly dependent on management practices. With a simulation model and the data from native, abandoned, and cultivated fields, we estimated that 25 to 120 g C m(-2) have been recovered on the abandoned fields during the past 50 yr. Such rates of recovery are small compared with loss rates due to cultivation. Rates of soil organic matter recovery are constrained by natural pedogenic processes, which cannot reverse disturbance processes at a comparable rate in this semiarid environment.