Carbon sequestration in a Brown Chernozem as affected by tillage and rotation

Abstract

Soil organic matter is important because it influences the productivity and physical well-being of soils. Recently, increased attention has focussed on soil organic matter as a possible sink for C02-C. Despite this interest, there is a lack of data for quantifying the effect of tillage on soil organic matter. Between 1981 and 1994, two tillage experiments were conducted at Swift Current, Saskatchewan, on Swinton loam, an Orthic Brown Chernozemic soil. Organic C and N were monitored periodically to quantify the effects of crop rotation [continuous spring wheat (Cont W) (Triticum aestivum L.) vs. fallow–wheat (F-W)] and tillage management [no-tillage (NT) vs. conventional tillage (CT) involving primarily use of a cultivator and rodweeder]. The effect of snow management on soil organic matter was also evaluated in one experiment, but this factor was not significant. Organic matter changes were mainly observed in the 0- to 7.5-cm soil depth. Carbon and N were greater in both concentrations and amounts in Cont W than in F–W; the latter cropping system was employed on this land during the previous 70–80 yr. In the 0- to 7.5-cm depth, the amount of organic matter was only moderately greater in NT than CT in the Cont W systems while in the F-W systems tillage was not significant (P > 0.10). During the 12-yr period, Cont W (average of NT and CT) gained about 2 t ha−1 more C in the top 15 cm of soil than F-W (average of NT and CT), with most of the increase occurring in the first 5 yr. Further, Cont W (NT) gained about 1.5 t ha−1 more C than Cont W (CT), and F-W (NT) gained about 0.5 t ha−1 more than F-W (CT). When a system that was maintained as Cont W (NT) for 9 yr was changed to Cont W (CT) for 3 yr and then summerfallowed (CT) for 1 yr, soil organic matter declined (P < 0.05). Our observations, supported by calculations based on crop residue production, indicated that an increase in organic C, averaging about 0.4–0.5 t ha−1 yr−1, has occurred in the top 15 cm of soil in Cont W (NT) between 1982 and 1993. However, because of uncertainty in our estimated C levels at the start of the experiment, the nature of the rate of C increase (linear or curvilinear) is not known. Key words: Organic C, organic N, no-till, summerfallow