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

Abstract

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.