Presentation on theme: "Some Perspectives of Carbon Sequestration in Agriculture Julian J. HUTCHINSON, Con CAMPBELL and Ray DESJARDINS Agriculture and Agri-Food Canada – Ottawa,"— Presentation transcript:
Some Perspectives of Carbon Sequestration in Agriculture Julian J. HUTCHINSON, Con CAMPBELL and Ray DESJARDINS Agriculture and Agri-Food Canada – Ottawa, CANADA
Overview Kyoto Protocol In 1987, the Bruntland Report – “Our Common Future” published by the World Commission on Environment and Development, focussed world attention on problems such as global warming, ozone depletion, desertification, reduced biodiversity, the burgeoning demands of a growing world population, and the need for a global agenda directed to sustainable development. Greenhouse Gases Looking only at C sequestration not CH 4 or N 2 O; Though we realize that CO 2 mitigating practices may influence CH 4 and N 2 O emission.
Carbon Sequestration C-sequestration is removal of CO 2 from the atmosphere and it’s storage either terrestrially or in oceans; Limiting work to agricultural soils; Not looking at oceans and forest soils as “sinks”.
Permanence Although C sequestered in soil is deemed to be permanently locked-up, we recognize that, in fact, such C can be released as CO 2 if the process by which it is locked-up (e.g., no-tillage) is reversed.
Equilibrium levels of soil C soils are not able to indefinitely accrue C; Soil C will change in response to a change in land management and C will eventually (30 – 50 years) achieve an equilibrium point which will not be exceeded unless management is changed or weather changes markedly; maximum potential carbon gain, therefore, is the difference between the current carbon status and that eventual equilibrium value.
Introduction 1 Sequestration of carbon greatest in regions where virgin soils had the greatest quantity of C prior to breaking for agriculture: These areas are primarily those that were developed under native grass vegetation, such as Chernozemic soils, especially Dark Brown, Black and Grey- Black Chernozems (i.e., Typic and Udic Borolls,) and are present in cooler climates;
Introduction 2 Such soils are mainly located in the Great Plains of North America and the former Soviet Union. Other areas of the world with high potential to sequester C are probably the Pampas of Argentina and the Veld of South Africa; These soils have the potential to sequester much C in arable land because primary production is high while cool, relatively dry conditions are conducive to high C inputs and low rates of decomposition and C mineralization.
Introduction 3 There are countries in the tropics and sub- tropics with large land mass of arable soils (e.g., Brazil, South-east Asia, some parts of Africa) where there is potential to sequester C: But rate of sequestration is low because even where primary production of crops is great, rate of decomposition and mineralization of SOC is great due to high temperatures and thus SOC storage is usually small; Soils are usually much lower in C than Chernozemic soils.
Köppen Climate Regions The modified Köppen (Koppen, 1928) classification divides the world into six major climate regions, based on average annual precipitation, average monthly precipitation, and average monthly temperature: A for tropical humid B for dry C for mild mid-latitude D for severe mid-latitude E for polar H for highland (this classification was added after Köppen created his system). H for highland
Introduction N. America For 6 months out of the year, it is cold (Canada: 0 - 5ºC mean annual temp.); Generally low in precipitation (average on Great Plains is approx. < 300 cm); Bare fallow is common in the semi-arid plains; Common crops include: cereals, oilseeds and pulses; Native soil is generally grassland; Rich in SOC (mainly Chernozemic soils).
North America - Canada Alberta Saskatchewan Manitoba Cordilleran region Indian Head Gray (Alfisol) Dark Gray Black (Udic Boroll) Dark Brown (Typic Boroll) Brown (Aridic Boroll) Beaverlodge Lacombe Lethbridge Swift Current Melfort Saskatoon Brandon Winnipeg Canadian Shield Alberta Saskatchewan Manitoba Cordilleran region Soil Zone Indian Head
Effect of Tillage and Cropping Frequency * *Relative to tilled, continuously cropped control. (F – Crop = 50 %, F – Crop - Crop = 66 %, Cont. Crop = 100 % cropping frequency).
Effect of Nutrient Addition F-WF-W-W Cont W Organic C (Mg ha -1 ) Unfert Fert LSD (P<0.05) = 3.0 (After 40 years on a thin Black Chernozem at Indian Head, Saskatchewan).
Effect of Forage in Rotation on Soil C (0 – 15 cm depth) 31.1 (2.2)Grass (N + P) 32.2 (1.4)LGM-W-W (N + P) 33.4 (1.0) y F-W-W (N + P) Mg ha -1 Swinton sil (Brown Chernozem) Bow Island, AB ( ) Bremer et al. (2002) 23.2Grass 20.9F-W-W (N + P) 20.2F-W (N + P) Mg ha -1 Bow Island, cl (Brown Chernozem) Swift Current, SK ( ) Campbell et al. (2000b)
Effect of Forage in Rotation on Soil C (0 – 15 cm depth) 34.5F-W-W-H-H-H (no fert.) 31.2LGM-W-W (no fert.) 28.0F-W-W (no fert.) Mg ha -1 Indian Head c (Black Chernozem) Melfort, SK (1957 – 1987) Campbell et al. (1991) 63.6F-W-W-H-H-W (N + P) 64.0LGM-W-W (N + P) 61.2F-W-W (N + P) Mg ha -1 Melfort sil (Black Chernozem) Indian Head, SK (1957 – 1997) Campbell et al. (2000a)
Accumulated Departure from Long-Term Mean Growing Season Precip. at Swift Current, SK Year Cumulative Departure
Effect of Weather on SOC Accumulation Cumulative Departure From Mean Precip. (e.g., Swift Current, Saskatchewan) Rate of SOC Increase in 0 – 15 cm depth (kg ha -1 y -1 ) Year Below average precip. Above average precip. “Normal” precip Fal. Cont
Effect of Increased Residue Inputs y = 0.01x R 2 = Mean Residue C inputs per rotation (kg/ha/yr) Mean Soil Organic C (Mg/ha) (e.g., Indian Head, Saskatchewan)
Effect of Crop Type F-W-W F-Flx-W F-Ry-W Cont W W-Lent Mean annual gain in SOC (kg ha -1 yr -1 ) (All systems received N+P) Measured (Based on a 36 year study on a Brown Chernozem at Swift Current, Saskatchewan).
North America – U.S.A. Generalized soils and climate map of the grassland region of the North American Great Plains.
Introduction - U.S.A. U.S. soils represent a substantial sink for C Recent trends in management on cropland includes reduced tillage, and conversion of annual cropland to permanent cover and forest ecosystems, including the CRP (Conservation Reserve Programme) and conservation buffers Mineral soils make up the vast majority of agricultural soils in the U.S.A..
Effect of Tillage (Paustian et al., 1997)
Effect of Cropping Frequency (on SOC in 0 – 20 cm depth) (Changes after 10 years of no-till on 3 sites in Colorado which were in conventional till F – Crop during previous years). Change in SOC (Mg ha - 1 ) Cropping Frequency (%) Sterling (Low PET) Stratton (Medium PET) Walsh (High PET) Summit Sideslope Toeslope
Summerfallow Area- U.S. A. Northern Great Plains
Effect of Grassland Conversion PracticeAmount C sequestered (Range) (Mg C/ha/yr) Investigators Improved grassland management 0.59 (Canada/U.S.A.) Conant et al., – 0.3Lal, 2001 Converting cultivated lands to grasslands 1.01Conant et al., 2001 Reduction of summer fallow 0.05 – 0.4Lal, 2001 (Amount of C sequestered in agricultural soils for various management practices).
Effect of Nutrient Amendment Includes commercial fertilizers and organic amendments Favours soil carbon gains by increasing yields and, consequently, the amount of residue returned to the soil; Animal manure is also effective in building soil C stocks ; Through benefits to soil fertility and structure; Manure is direct addition of C; however, application can increase crop growth and thereby contribute to C gains from higher plant litter.
Tropics Part of the Earth's surface between the Tropic of Cancer (23.5ºN) and the Tropic of Capricorn(23.5ºS); Characterized by a hot climate;
Introduction - Tropics Tropical agriculture is highly diverse, ranging from intensive, highly developed management systems to extensive, low input subsistence production; largely subsistence-based; generally low production inputs; low C soils; high demand for alternative uses of crop residues; agriculture land-base is expanding, resulting in large losses of biomass and soil C due to deforestation;
Introduction - Tropics Tropical region will be discussed as 3 sub-groups: Semi-arid Tropics Sub-humid Tropics Humid Tropics
Semi-arid Tropics Includes parts of Central and South America (e.g., Argentina, North-east Brazil) some parts of West, East and Southern Africa and (annual precipitation averages < 100 cm): predominant native vegetation is savannah and forest and agricultural systems are mainly grazing, shifting cultivation and dry-land agriculture; Soil C is inherently low (about 25 Mg C ha -1 ); After clearing (e.g., fire), C loss is rapid (30 – 50 % in 6 years); limited available water, high temperatures and relatively low fertility results in high rate of residue mineralization and low C inputs to soil; poor management of crop residues (e.g., used as fuel); limited opportunities to sequester much C in soils.
Sub-humid Tropics Large parts of the African continent, major part of Indian sub-continent and continental South- east Asia, parts of Latin America and Australia: Annual rainfall average 100 – 200 cm; native vegetation is tropical deciduous or dry forests; in poorer soils, extensive grazing is used in combination with subsistence agriculture; in the more humid areas fertilization, weed control and species selection are used to maximize production;
Sub-humid Tropics (cont’d) shifting cultivation and fallow rotation is also practiced; ploughing in seed-bed preparation causes rapid decline in soil C to as low as 8 – 15 Mg C ha -1 in < 10 years; use of improved fallows and cover crops within cropping sequences, and woody species in agro-forestry systems have increased C in soils; best strategies are to improve soil physical conditions by conservation tillage, mulch farming, improved fallows, cover-crops and agro-forestry; C inputs and soil C also enhanced by fertilizers and manure.
Humid Tropics Large areas in South America (e.g., the Amazon), and Africa (e.g., the Congo), and South-east Asia; very high annual rainfall (> 200 cm): tropical evergreen forests; crop production limited by low fertility and soil acidity due to leaching; some reports of similar or higher C levels under pasture compared to the native forest from which they were derived; C sequestration potential in moist tropical pastures can be significant under favourable conditions; sound management practices are essential to realize this potential for reducing C losses from land-use conversions.
Tropics - General Single most significant mitigation option related to agriculture in the tropics is to reduce the pressure for converting new (forested) land to agriculture.
Concluding Remarks Value of incentives for progressive producers Governments have a difficult problem to contend with if they reward producers who adopt best management techniques and sequester C and refuse to reward producers who, because they had the foresight to adopt such management several years in the past, are not rewarded for the C that they had sequestered. This is especially troublesome if the latter farmers’ soils are now approaching equilibrium levels of soil C therefore making it difficult to sequester more C in the soil.
Concluding Remarks (cont’d) Trading concerns Commercial companies wishing to trade with farmers for sequestered C must bear in mind the inherent difficulties in making accurate measurements of C sequestered, especially over short periods (< 5 years). They may be better off to purchase such C as “offsets” by paying farmers to adopt “best management practices” which scientists have demonstrated will sequester C than to rely on measurements of absolute gains in soil C. Spatial variability makes this a challenging proposition.
Concluding Remarks (cont’d) Weather the main constraint to C sequestration Because C sequestration is a function of primary production and rate of organic matter decomposition, the most important factor influencing sequestration is weather (moisture and temperature). Thus the amount of C sequestered depends on weather conditions over which we have no control. Projections of C sequestration are therefore always going to be tenuous at best on this subject.
Concluding Remarks (cont’d) Rewards for Adopting Best Management Practices Fortunately, the same best management practices that will enhance C sequestration in soil are precisely the ones which will lead to greater net returns, reduced risk, more efficient energy use and often, improved environmental quality. Thus, producers will likely be willing to adopt such practices as reduced tillage, use crop rotations instead of monocultures, increase cropping frequency at the expense of bare fallow in arid and semi-arid environments, grow forage crops on marginal land and make more efficient use of fertilizers by using soil test criteria, all of which are positive alternatives for reducing CO 2 emissions and increasing C sequestration.