Cultivation and Reseeding Effects on Soil Organic Matter in the Mixed Prairie

This study investigated how disturbances from cultivation and haying altered the soil organic C (SOC) at two sites: one (Lethbridge) in a Stipa – Agropyron – Bouteloua community (49°7″ N, 112°57″ W) and a second (Onefour) in a more xeric Stipa – Bouteloua community (49°3″ N, 110°27″ W). Seven disturbance treatments were established on previously uncultivated native grassland to assess their effect on SOC 12 or 13 yr after establishment. A randomized complete block design with four replicates was used. Soils were sampled in the fall of 1995, 1997, and 2006 at two increments (0–15 and 15–30 cm) and a third (30–90 cm) was sampled in 2006. The soils were all analyzed for their SOC and, in 2006, also for their light fraction organic C (LF OC) and mineralizable C. Breaking and immediate establishment of perennial grass monocultures had no effect on SOC, LF OC, or mineralizable C. Wheat ( Triticum aestivum L.) cropping (either fallow or continuous) resulted in a 19% loss of SOC after 13 yr. The rate of loss varied from an average of about 1.7 Mg ha −1 yr −1 in the first 4 yr to about 0.32 Mg ha −1 yr −1 in the subsequent 9 yr. These results are consistent with a more rapid loss of SOC in the first decade of cropping virgin soils, a slowing rate of loss, and a new steady state within a few decades.