Effects of crop rotation, crop type and tillage on soil organic carbon in a semiarid climate

Shrestha, B. M., McConkey, B. G., Smith, W. N., Desjardins, R. L., Campbell, C. A., Grant, B. B. and Miller, P. R. 2013. Effects of crop rotation, crop type and tillage on soil organic carbon in a semiarid climate. Can. J. Soil Sci. 93: 137-146. There is uncertainty about how crop rotation and tillage affect soil organic C (SOC) on the Canadian prairies. We compared SOC amount and change (Delta SOC) for one continuous crop and four 3-yr fallow-containing crop rotations under no-tillage (NT), and two fallow-containing crop rotations under minimum-tillage (MT), from 1995 to 2005 in semiarid southwestern Saskatchewan. After 11 yr, SOC (0- to 15-cm depth) was 0.2 Mg C ha(-1) higher under continuous crop compared with fallow-containing systems. There were no significant differences in SOC and Delta SOC among fallow-containing rotations or between MT and NT. Total C inputs were weakly (R-2 =0.18) but significantly (P <0.05) correlated to Delta SOC, which changed by +/- 0.33 Mg C ha(-1) for each Mg ha(-1) C input above or below 2.4 Mg C ha(-1) yr(-1). Carbon inputs were typically less than this amount and SOC generally decreased over the experiment. Simulations of SOC with the Century model were consistent with our observations regarding Delta SOC per unit of C input. There was slight loss of SOC for the above-average precipitation regime during the study. Simulations also supported our finding that SOC differences between crop mix and tillage systems may require several decades to become distinguishable in this semiarid climate with small and variable C inputs.