Quantifying carbon sequestration in a minimum tillage crop rotation study in semiarid southwestern Saskatchewan

Abstract

. Quantifying carbon sequestration in a minimum tillage crop rotation study in semiarid southwestern Saskatchewan. Can. J. Soil Sci. 87: 235-250. Scientists and the agricultural community require methods of quantifying C sequestration in soils. This is important in assessing the impact of crop management practices on emission of greenhouse gases and for "C trading". Using simulation models may be a more effective method of quantification as compared with in situ measurements. A 17-yr crop rotation experiment being conducted on a medium-textured Orthic Brown Chernozem at Swift Current, Saskatchewan, in which soil organic C (SOC) was being monitored periodically, was used to assess the effect on C sequestration of cropping frequency, wheat class, legume green manure (LGM), flexible cropping based on available water, and regrassing of crop land. Prior to the study, the experimental site had been cropped to fallow-wheat (F-W) for the previous 60 yr. Crop management in this experiment involved minimum tillage, snow trapping, and N + P fertilization based on soil tests. Three models [Century, the Introductory C Balance model (ICBM), and the Campbell model] were tested for their effectiveness in simulating SOC trends. Because growing season precipitation was average to above average, yields, and thus C inputs from residue, were also above average, and consequently SOC increased in most systems for the first 10 yr before reaching a new steady state. SOC gains (kg ha -1 yr -1 ) in the 0-to 15-cm depth in 17 yr were directly proportional to cropping frequency (F-W-W = 135, F-W-W-W = 332, and Cont W = 441);LGM-W-W gained SOC at a much higher rate than F-W-W (329 vs. 135 kg ha -1 yr -1 ); Canada Western Red Spring (CWRS) wheat (Triticum aestivum L.), although it yielded 26% less than Canada Prairie Spring (CPS) wheat, gained SOC at a higher rate than CPS wheat (135 vs. 0 kg ha -1 yr -1 ). Further, 2 yr of conventionally-tilled fallow in 17 yr (flexible system) markedly suppressed SOC gain by 46% compared with Cont W (441 vs. 236 kg ha -1 yr -1 ). There was a 282 kg ha -1 yr -1 gain in SOC under crested wheatgrass (Agropyron cristatum L.) (CWG) but most of this gain occurred in the last 7 yr. Though having their inherent weaknesses, the ICBM and Campbell models performed equally well in simulating SOC trends (r 2 = 0.55 ** ), but Century was less effective (r 2 = 0.21 * ), in part because of its limited ability to simulate yields. Because C input, and thus yield, is one of the main factors influencing SOC gains, and since measured yields are used in the ICBM and Campbell models, while simulated yields are used by Century, the ICBM and Campbell models have an advantage over the Century model in this comparison. Efficiencies of conversion of input C to SOC increased with cropping frequency, and were higher for LGM-W-W than for F-W-W, and for systems with CWRS wheat rather than CPS wheat. Efficiency of conversion was 8% for F-W-W, 15% for LGM-W-W and 21% for Cont W.Key words: ICBM model, Century model, Campbell model, C sequest...

Soils and food sufficiency. A review

“…Similar to the data from the US, the positive impact of residue mulch and NT farming on the SOM pool have been reported by several studies in Canada Campbell et al, 2007;Janzen, 2006;Wang et al, 2006;Liang et al, 2005;Singh and Malhi, 2006;Gregorich et al, 2006). These conclusions of improvements in soil quality are also supported by the data from Europe and Australia.…”

“…Soil C pool: It is widely recognized that conversion of plow till to NT leads to C sequestration in soils (Campbell et al, 2007;Sa et al, 2001;West and Post, 2002;Vagen et al, 2005). These are some concerns about the hidden C costs (Schlesinger, 2006), and the net C gains.…”

Estimated soil organic carbon change due to agricultural land management modifications in a semiarid cereal-growing region in Central Spain

“…However, there were differences between the management scenarios where the addition of vetch rotations increased SOC due to their input. Similar conclusions were found by Campbell et al (2007) where legume green manure resulted in higher gains in SOC over a 17-year testing period when compared with rotations that included only wheat and fallow. The highest SOC and humus were for PA on CL soil texture, with SOC at 67.3 T ha À1 and humus 23.5 T ha À1 at the end of the end of the 100-year modelling run.…”

Sequestering carbon in minimum-tilled clay soils used for irrigated cotton and grain production

“…Firstly, the loss of the stubble-C from the soil is decreased where the stubble C:N ratio is narrow (Suman et al, 2006) so that stubble-C is more completely incorporated into the soil microbial biomass and secondly, N 2 O emissions are small where legumes and little or no fertiliser-N are used (Rochette and Janzen, 2005). Curtin et al (2000) and Campbell et al (2007) suggested that legume crops promoted the conversion of stubble-C to soil SOC, as was evident in the experiment. Mortenson et al (2004) found SOC increased by up to 17% over 33 years where Medicago sativa was sown into native pasture.…”

“…Crops that are irrigated and optimally fertilised may produce more biomass and therefore more stubble (Campbell et al, 2001;Follett et al, 2005). SOC can increase where minimum or reduced tillage is adopted and long fallows eliminated from the cropping system (Campbell et al, 2007;Bremner et al, 2008).…”