Long-term effects of tillage and fallow-frequency on soil quality attributes in a clay soil in semiarid southwestern saskatchewan

Abstract

Reduced tillage management is being adopted at an accelerated rate on the Canadian prairies. This may influence soil quality and productivity. A study conducted on a clay soil (Udic Haplustert) in southwestern Saskatchewan, Canada, to determine the effects of fallow frequency [fallow-wheat (F-W) vs. continuous wheat (Cont W)] and tillage [no-tillage (NT) vs. conventional (CT) or minimum tillage (MT)] on yields of spring wheat ( Triticum aestivum L.), was sampled after 3, 7 and 11 years to assess changes in selected soil quality attributes. Tillage had no effect on amount of crop residues returned to the land, but the tilled systems had significantly ( P<0.05) lower total organic C and N in the 0–7.5 cm soil depth, though not in the 7.5–15 cm depth. Further, these differences were observed after only 3 years and persisted for the entire 11 years of the study. For example, in the 0–7.5 cm depth, organic C in F-W (MT) after 3 years was 10 480 kg ha −1 and in F-W (NT) 13 380 kg ha −1, while in Cont W (CT) and Cont W (NT) corresponding values were 11 310 and 13 400 kg ha −1, respectively. After 11 years, values for F-W (MT) and F-W (NT) were 11 440 and 14 960 kg ha −1, respectively, and for Cont W (CT) and Cont W (NT), 12 970 and 16 140 kg ha −1, respectively. In contrast to total organic matter, two of the more labile soil quality attributes [i.e., C mineralization (C min) and N mineralization (N min)] did not respond to fallow frequency until after 7 years and only in the 0–7.5 cm depth. Microbial biomass (MB) and the ratio of C min to MB [specific respiratory activity (SRA)], two attributes also regarded as labile, were not influenced by the treatments even after 11 years. After 11 years, only C min and N min among the labile soil quality attributes responded to the treatments. Surprisingly, the labile attributes were no more sensitive to the treatments than was total organic C or N. More research is required to determine why responses in this soil differed from those reported elsewhere.