Long-Term Effects of Land Use and Cropping System on Soil Quality in a Semi-Arid Climate.

Diversified no-till (NTCS) cropping systems that include pulse or oilseed crops are being adopted in the northern Great Plains to reverse soil degradation promoted by a century of fallow-wheat systems. However, the long-term impact of NTCS on soil quality and biogeochemistry is not fully understood. We examined the influence of land use and cropping system on the stock of total carbon (TC), soil inorganic carbon (SIC), soil organic carbon (SOC), and total nitrogen (TN); and on the concentration of labile C and N fractions, permanganate oxidizable carbon (POXC) and potentially mineralizable nitrogen (PMN) of a Judith clay loam from central Montana at a long-term experiment (10 years). Soil samples were collected from the 0–10, 10–20, 20–30, and 30-40 cm of fallow-winter wheat (Triticum aestivum L.) (F-W), camelina (Camelina sativa L. Crantz)-winter wheat (C-W), and camelina-spring pea (Pisum sativum L.)-winter wheat (C-S-W) crop rotations under no-till (NT) and sweep-till (ST) fields, and of the adjoining soil under native vegetation (NV). Cultivation of NV has resulted in losses of 16-28 % of the original SOC stock of 0-40 cm. Cumulative TC and SOC was not significantly different among the six cropping systems when the whole soil profile was analyzed. Accumulation of SIC ranged from 54.22 to 103.47 Mg ha^-1 and was lowest under NV relative to NT and ST cropping systems. In general, significant differences in POXC and PMN were confined to the surface soil (0-20 cm), following the order NV> all cropping systems; although lowest POXC values were measured in the C-S-W rotation in both ST and NT fields. Results suggest that soil C differences between cropping systems may require several decades to become apparent in this semi-arid environment where the potential of soils to sequester C is largely controlled by sporadic water availability and erratic crop productivity.