Soil erosion due to human activity impairs agricultural productivity and puts valuable wildlife habitat at risk for conversion into cropland. The present study sought to gain insight into the mechanisms of erosion through evaluating the erodibility of central Ohio soils under management regimes of contrasting intensity. Erodibility was examined at 2 adjacent agricultural fields managed for at least 10 years under respective regimes of no-tillage and conventional tillage (i.e., chiseling in the fall and disk harrowing in the spring). Measured soil properties included texture, organic carbon content, bulk density, wet aggregate stability, water-holding capacity, saturated hydraulic conductivity, residue coverage, and permanganate-oxidizable carbon content (POXC). Due to the temporal variability of many of these properties, measurements were carried out in both the spring and fall of 2014. In order to better isolate the impact of management regime on soil properties, both study fields were sampled according to landscape position (e.g., upland, lowland, and terrace), and comparisons between fields were performed primarily among samples matched in terms of both landscape position and season. Correlations among measures were also examined, and each field was additionally evaluated using 3 erosion assessment tools: the Universal Soil Loss Equation (USLE), the Revised Universal Soil Loss Equation 2 (RUSLE2), and a systems-engineering framework described by Karlen and Stott (1994).
Significant differences (p < 0.05) between fields were found for most soil properties sampled within the same landscape position and season, and differences were most pronounced for aggregate stability and residue coverage. Correlations among properties revealed that organic carbon was well correlated with bulk density, water-holding capacity, and POXC, and weakly correlated with aggregate stability. POXC was slightly better correlated with aggregate stability than was organic carbon, but it still could only minimally account for the observed variation in wet-aggregate stability. It therefore appears that other factors are influencing aggregation, and it is hypothesized that one destabilizing factor may be heterogeneity of aeration on the aggregate scale, which is potentially increased through tillage. In poorly-drained tilled soils, such as the tilled lowland of the present study, aeration heterogeneity may work to segment larger aggregates by focusing oxidation upon discrete points along otherwise protected organic fragments. This hypothesis merits further investigation.
Annual soil losses predicted for the tilled field by the USLE and RUSLE2 were 10.6 and 8.9 tons per acre, respectively. These values are far in excess of the tolerable soil loss, or “T-value,” which these tools identify to be 3.0 tons per acre. Soil losses predicted by the USLE and RUSLE2 for the no-till field, by contrast, were 1.3 and 1.7 tons per acre, annually. In keeping with these values, the systems-engineering framework rated the erosion resistance of the no-till and tilled fields to be 0.55 and 0.21, respectively.
These findings support the notion that tillage disrupts soil structure and leads to heightened erosional losses. Due to the ability of percent residue coverage and wet-aggregate stability to discriminate between land areas of contrasting erodibility, it is recommended that future erodibility assessments include these two measurements.
Keywords: soil erosion, tillage, organic carbon, POXC, aggregate stability, Ksat, residue, bulk density, water-holding capacity, aeration heterogeneity, oxygenation, RUSLE2, USLE, occluded, mucilage, particulate