Sink Potential of Canadian Agricultural Soils

Soil Use and Management, 1997

Agricultural soils, having been depleted of much of their native carbon stocks, have a significant COz sink capacity. Global estimates of this sink capacity are in the order of 20-30 Pg C over the next 50-100 years. Management practices to build up soil C must increase the input of organic matter to soil and/or decrease soil organic matter decomposition rates. The most appropriate management practices to increase soil C vary regionally, dependent on both environmental and socioeconomic factors. In temperate regions, key strategies involve increasing cropping frequency and reducing bare fallow, increasing the use of perennial forages (including N-fixing species) in crop rotations, retaining crop residues and reducing or eliminating tillage (i.e. no-till). In North America and Europe, conversion of marginal arable land to permanent perennial vegetation, to protect fragile soils and landscapes and/or reduce agricultural surpluses, provides additional opportunities for C sequestration. In the tropics, increasing C inputs to soil through improving the fertility and productivity of cropland and pastures is essential. In extensive systems with vegetated fallow periods (e.g. shifting cultivation), planted fallows and cover crops can increase C levels over the cropping cycle. Use of no-till, green manures and agroforestry are other beneficial practices. Overall, improving the productivity and sustainability of existing agricultural lands is crucial to help reduce the rate of new land clearing, from which large amounts of C 0 2 from biomass and soil are emitted to the atmosphere. Some regional analyses of soil C sequestration and sequestration potential have been performed, mainly for temperate industrialized countries. More are needed, especially for the tropics, to capture region-specific interactions between climate, soil and management resources that are lost in global level assessments. By itself, C sequestration in agricultural soils can make only modest contributions (e.g. 3+%0 of total fossil C emissions) to mitigating greenhouse gas emissions. However, effective mitigation policies will not be based on any single 'magic bullet' solutions, but rather on many modest reductions which are economically efficient and which confer additional benefits to society. In this context, soil C sequestration is a significant mitigation option. Additional advantages of pursuing strategies to increase soil C are the added benefits of improved soil quality for improving agricultural productivity and sustainability.

Geoderma, 2019

Soil organic carbon (SOC) in agricultural lands is vital for global food production and greenhouse gas (GHG) mitigation. Accurate quantification of the change in SOC stocks at regional or national scales, which depends heavily on reliable spatiotemporal carbon (C) input data, remains a big challenge. Here we use the process-based RothC model to estimate change in SOC stocks across Canada for 1971 to 2015, based on calculated annual C flows between cropland and livestock sectors. Total C input to 0-20 cm soils from crops, manure, and biosolids in Canada increased by 81% from 1971 to 2015, which shifted Canadian agricultural lands from a CO 2 source before 1990 (−1.1 Tg C yr −1) to a small sink during 1990-2005 (4.6 Tg C yr −1), and a larger sink thereafter (10.6 Tg C yr −1). The increasing trend of SOC stocks is mainly driven by the increases in crop yield; the enhanced C sink since 2005 reflects increasing C input largely driven by the increasing area and yield of canola. SOC sequestration showed a potential to offset~34% or more of agricultural GHG emission since 1990. Increasing crop yields and adopting crop mixes that input proportionately more below-ground C, such as canola and oat, showed potential additional opportunity to sequester SOC, estimated at 1.7 Tg C yr −1 for 2016-2030 in Canada. This study illustrates that SOC sequestration is driven largely by plant C inputs, and shows that agronomic measures which augment C input through crop choices and yield-enhancing practices can profoundly benefit climate mitigation strategies.

Climatic Change, 2005

Carbon sequestration in agricultural soils is frequently promoted as a practical solution to slow down the rate of increase of CO 2 in the atmosphere. There is a need to improve our understanding on how land management practices affect exchange processes that lead to N 2 O emissions, CH 4 absorption and net removal of atmospheric CO 2 . In this paper we review the magnitude of the impact of management practices such as no-tillage, summer fallow, introduction of forages into crop rotations, conversion of croplands to grasslands, nutrient addition via fertilization as a means to increase C sequestration in agricultural soils. Using CENTURY (a C model) and DNDC (a N model) we ran simulations for five locations across Canada, for a 30-year time period, examining the potential trade-off between C sequestration and increased N 2 O emissions. These simulations showed that the conversion of croplands to grasslands resulted in the largest reduction in net GHG emissions, while nutrient additions via fertilizers resulted in a small increase GHG emissions. The CENTURY model was also used to demonstrate that climate variations during the last 25 years could account for a change of 6% in the soil C at a site in Alberta,

In 1990, primary agriculture contributed 10% of the anthropogenic greenhouse gas emissions in Canada while the whole agriculture and agri-food sector contributed 15%. By 2010, greenhouse gas emissions from primary agriculture are expected to have increased by about 8 Tg CO 2 equivalent. In order to examine the potential of this sector to reduce its emissions, we investigated the effects of several carbon (C) sequestration strategies on the greenhouse gas budget. We estimated, using the Century model (April 1999 version), the change in soil carbon associated with the implementation of four management practices: 1) An increase in the acreage of no-till farming from 14% in 1996 to 30% by 2010 would result in an average sequestration of 1.15 Tg yr -1 C. 2) A reduction in the acreage of cropland under summer fallow by 2.8 million hectares (Mha) for the Chernozemic soils in the Prairies would result in an increase in soil C of 0.46 Tg yr -1 C. 3) An increase in N fertilizer by 50% would increase soil C storage by another 0.26 Tg yr -1 C. 4) An increase in the acreage of perennial grass cover from 15% to 19% would increase soil carbon sequestration by 0.60 Tg yr -1 C. These changes in carbon storage, which are based on a 20-year average, are equal to 2.5 Tg yr -1 C. Such changes are equivalent to reducing agricultural emissions by 9.2 Tg yr -1 CO 2 , which is about 80% of the amount required by the primary agriculture sector to meet its part of the Kyoto commitment. Considering that these estimates were made on only about two thirds of the croplands and for only four mitigation measures, increased C storage in agricultural soils appears to be a viable approach to help Canada meet part of its international commitment. However, emissions of other greenhouse gases associated with these mitigation measures could negate a substantial part of the gains obtained from carbon sequestration.

Nutrient Cycling in Agroecosystems, 2001

The possibility that the carbon sink in agricultural soils can be enhanced has taken on great political significance since the Kyoto Protocol was finalised in December 1997. The Kyoto Protocol allows carbon emissions to be offset by demonstrable removal of carbon from the atmosphere. Thus, forestry activities (Article 3.3) and changes in the use of agricultural soils (Article 3.4) that are shown to reduce atmospheric CO2levels may be included in the Kyoto emission reduction targets. The European Union is committed to a reduction in CO2 emissions to 92% of baseline (1990) levels during the first commitment period (2008–2012). We have shown recently that there are a number of agricultural land-management changes that show some potential to increase the carbon sink in agricultural soils and others that allow alternative forms of carbon mitigation (i.e. through fossil fuel substitution), but the options differ greatly in their potential for carbon mitigation. The changes examined were, (a) switching all animal manure use to arable land, (b) applying all sewage sludge to arable land, (c) incorporating all surplus cereal straw, (d) conversion to no-till agriculture, (e) use of surplus arable land to de-intensify 1/3 of current intensive crop production (through use of 1/3 grass/arable rotations), (f) use of surplus arable land to allow natural woodland regeneration, and (g) use of surplus arable land for bioenergy crop production. In this paper, we attempt for the first time to assess other (non-CO2) effects of these land-management changes on (a) the emission of the other important agricultural greenhouse gases, methane and nitrous oxide, and (b) other aspects of the ecology of the agroecosystems. We find that the relative importance of trace gas fluxes varies enormously among the scenarios. In some such as the sewage sludge, woodland regeneration and bioenergy production scenarios, the inclusion of trace gases makes only a small (2-C mitigation potential. In other cases, for example the no-till, animal manure and agricultural de-intensification scenarios, trace gases have a large impact, sometimes halving or more than doubling the CO2-C mitigation potential. The scenarios showing the greatest increase when including trace gases are those in which manure management changes significantly. In the one scenario (no-till) where the carbon mitigation potential was reduced greatly, a small increase in methane oxidation was outweighed by a sharp increase in N2O emissions. When these land-management options are combined to examine the whole agricultural land area of Europe, most of the changes in mitigation potential are small, but depending upon assumptions for the animal manure scenario, the total mitigation potential either increases by about 20% or decreases by about 10%, shifting the mitigation potential of the scenario from just above the EU's 8% Kyoto emission reduction target (98.9 Tg C y−1) to just below it. Our results suggest that (a) trace gas fluxes may change the mitigation potential of a land management option significantly and should always be considered alongside CO2-C mitigation potentials and (b) agricultural management options show considerable potential for carbon mitigation even after accounting for trace gas fluxes.

Frontiers in sustainable food systems, 2019

Carbon sequestration on agricultural fields is feasible with a range of soil management approach and can be considerable with improved planning. Carbon sequestration of emitted carbon emissions is now essential to mitigate or unlikely to stabilize our altering atmosphere. There are many management technologies for removing carbon from the environment and fixing it in the soil. These approaches vary in their capacity among different climatic zones, soil types and land locations. At present it being a matter of debates about the duration and amount of carbon sequestration in agriculture fields and about the precise situations that increase lower down of carbon emissions.

International Journal of Current Microbiology and Applied Sciences, 2017

Soil and Tillage Research, 2005

Agricultural soils can constitute either a net source or sink of the three principal greenhouse gases, carbon dioxide (CO 2 ), nitrous oxide (N 2 O), and methane (CH 4 ). We compiled the most up-to-date information available on the contribution of agricultural soils to atmospheric levels of these gases and evaluated the mitigation potential of various management practices in eastern Canada and northeastern USA. Conversion of native ecosystems to arable cropping resulted in a loss of $22% of the original soil organic carbon (C)-a release of about 123 Tg C to the atmosphere; drainage and cultivation of organic soils resulted in an additional release of about 15 Tg C. Management practices that enhance C storage in soil include fertilization and legume-and forage-based rotations. Adopting no-till did not always increase soil C. This apparent absence of no-till effects on C storage was attributed to the type and depth of tillage, soil climatic conditions, the quantity and quality of residue C inputs, and soil fauna. Emission of N 2 O from soil increased linearly with the amount of mineral nitrogen (N) fertilizer applied (0.0119 kg N 2 O-N kg N À1 ). Application of solid manure resulted in substantially lower N 2 O emission (0.99 kg N 2 O-N ha À1 year À1 ) than application of liquid manure (2.83 kg N 2 O-N ha À1 year À1 ) or mineral fertilizer (2.82 kg N 2 O-N ha À1 year À1 ). Systems containing legumes produced lower annual N 2 O emission than fertilized annual crops, suggesting that alfalfa (Medicago sativa L.) and other legume forage crops be considered different from other crops when deriving national inventories of greenhouse gases from agricultural systems. Plowing manure or crop stubble into the soil in the autumn led to higher levels of N 2 O production (2.41 kg N 2 O-N ha À1 year À1 ) than if residues were left on the soil surface (1.19 kg N 2 O-N ha À1 year À1 ). Elevated N 2 O emission during freeze/thaw periods in winter and spring, suggests that annual N 2 O emission based only on growing-season measurements would be underestimated. Although measurements of CH 4 fluxes are scant, it appears that agricultural soils in eastern Canada are a weak sink of CH 4 , and that this sink may be diminished through manuring. Although the influence of agricultural management on soil C storage and emission of greenhouse gases is significant, management practices often appear to involve offsets or tradeoffs, e.g., a particular practice may increase soil C storage but also increase emission of N 2 O. In addition, because of high variability, adequate spatial and temporal sampling are needed for www.elsevier.com/locate/still Soil & Tillage Research 83 (2005) 53-72