Tillage and crop rotation effects on soil organic C and N in a coarse-textured typic haploboroll in southwestern Saskatchewan

An 11 year study conducted in the semiarid prairie of southwestern Saskatchewan, Canada, to determine the influence of fallow frequency and tillage on yields and economics of durum wheat (Triticum turgidum L.) production, was used to assess changes in soil organic C and N. The soil was a coarse-textured, Typic Haploboroll. Cropping frequency (fallow-wheat vs. continuous wheat) had no effect on organic C or N concentrations or amount in this study. Compared with conventional mechanical or minimum tillage, no-tillage increased organic C and N concentrations in the 0-7.5 cm soil depth during the final 4 years of the experiment when crop yields and residue production were above average. However, there was no effect of tillage on C or N concentration in the 7.5-15 cm depth, nor on the mass of organic C or N in either depth. The amount of organic C in the top 15 cm of soil increased by 1.6 t ha(-1) over the 11 year period (average for all systems). Most of this increase occurred in the final 4 years and was generally related to the amount of crop residues returned to the soil. Because neither rotation nor tillage influenced crop production, these practices did not affect organic C or N. We concluded that there was limited opportunity to sequester additional C in coarse-textured soils located in semiarid climates if monoculture cereal systems are used under conventional (mechanical) or no-tillage.