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.", Canadian Journal of Soil Science, 93(1), pp. 137-146. doi : 10.4141/CJSS2012-078  Access to full text

Abstract

There is uncertainty about how crop rotation and tillage affect soil organic C (SOC) on the Canadian prairies. We compared the effects of crop rotation (various sequences of wheat, oilseeds, and pulses) and tillage system on SOC amount and change (ΔSOC) for one continuous crop and four 3-year 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. The continuous crop rotation increased SOC in 0- to15- cm depth by 0.2 Mg C ha-1 over 11 years compared to fallow containing systems, although the effect was only significant in the 0- to 7.5- cm depth. There were no differences in SOC between the fallow containing rotations or between MT and NT systems. There was a weak (R2=0.18) but significant (P < 0.05) linear relationship between ΔSOC and total C inputs such that SOC increased or decreased by 0.33 Mg C ha-1 for each Mg C ha-1 that residue C input was greater than or less than 2.4 Mg C ha-1yr-1, respectively. Since, our C inputs were typically less than this amount, generally SOC decreased over the experiment. Type of crop or fallow did not affect the ΔSOC. Canola (Brassica napus L.), and pulse crops provided about 10% greater C inputs than durum wheat (Triticum durum L.). Wheat after canola provided about 0.2 Mg C ha-1 more inputs than wheat after wheat showing that crop diversification of rotations can also increase C inputs due to rotation effect. Simulations of SOC with the Century model were consistent with the observations regarding the rate of SOC increase per unit of C input, the slight loss of SOC during the above-average precipitation regime during the study, and that SOC differences between crop mix and tillage system may require several decades to become distinguishable in this semiarid climate with small and variable C inputs.

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