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 or N O; 4 2 Though we realize that CO mitigating practices may 2 influence CH and N O 4 2 emission.
Carbon Sequestration C-sequestration is removal of CO 2 from the atmosphere and it’s storage either terrestrial y 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 if the process by which it is 2 locked-up (e.g., no-til age) is reversed.
Equilibrium levels of soil C soils are not able to indefinitely accrue C; Soil C wil change in response to a change in land management and C wil eventual y (30 – 50 years) achieve an equilibrium point which wil 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) .
Introduction N. America For 6 months out of the year, it is cold (Canada: 0 – 5ºC mean annual temp.); General y low in precipitation (average on Great Plains is approx. < 300 cm); Bare fal ow is common in the semi-arid plains; Common crops include: cereals, oilseeds and pulses; Native soil is general y grassland; Rich in SOC (mainly Chernozemic soils).
North America – Canada Al A b l e b r e t r a t Ma M n a i n t i o t b o a b Sa S s a k s a k t a c t h c e h w e a w n a Canadian Shield Beaverlodge Soil Zone Corodidlere Gray (Alfisol) ana n Lacombe re Melfort gig o Dark Gray n Saskatoon Black (Udic Borol ) In I d n i d a i n a n H e H a e d Lethbridge a Dark Brown Winnipeg Swift Current (Typic Borol ) Brandon Brown (Aridic Borol )
Effect of Tillage and Cropping C Frequency O S Ti T l i l l e l d e 30 3 0 0 Br B o r w o n w n a n a d n 00 d Dk D Br B o r w o n w in No N o T i T l i l Brown and in ll Brown and eg Ti T l i l l e l d e n 20 2 0 0 Bl B a l c a k c k a n a d n d G r G e r y e a No N o T i T l i l Black and Gr a ll Black and G h c ) 1* 10 1 0 0 e – e r tiv y tiv 1 la – a la 0 h l re g l re a (k -10 1 0 0 unn -20 2 0 0 anae -30 3 0 0 M 0 20 2 40 4 60 6 80 8 10 1 0 0 12 1 0 2 Cr C o r p o p p i p n i g n g F r F e r q e u q e u n e c n y c y ( % ( ) % *Relative to til ed, (F – Crop = 50 %, F – Crop – Crop = 66 %, continuously cropped control. Cont. Crop = 100 % cropping frequency).
Effect of Nutrient Addition Unfert Fert LSD (P<0.05) = 3.0 40 ) 35.1 36.4 -1 31.4 33.0 30.2 30.8 a 30 hg (M 20 ic C 10 anrg 0 O F-W F-W-W Cont W (After 40 years on a thin Black Chernozem at Indian Head, Saskatchewan).
Effect of Forage in Rotation on Soil C (0 – 15 cm depth) Swift Current, SK (1987 – 1996) Campbel et al. (2000b) Mg ha-1 Swinton sil (Brown Chernozem) 33.4 (1.0)y F-W-W (N + P)LGM-W-W (N + P) 32.2 (1.4) Grass (N + P) 31.1 (2.2) Bow Island, AB (1992 – 1997) Bremer et al. (2002) Mg ha-1 Bow Island, cl (Brown Chernozem) F-W (N + P) 20.2 F-W-W (N + P) 20.9 Grass 23.2
Effect of Forage in Rotation on Soil C (0 – 15 cm depth) Indian Head, SK (1957 – 1997) Campbel et al. (2000a) Mg ha-1 Indian Head c (Black Chernozem) F-W-W (no fert.) 28.0 LGM-W-W (no fert.) 31.2 F-W-W-H-H-H (no fert.) 34.5 Melfort, SK (1957 – 1987) Campbell et al. (1991) Mg ha-1 Melfort sil (Black Chernozem) F-W-W (N + P) 61.2 LGM-W-W (N + P) 64.0 F-W-W-H-H-W (N + P) 63.6
Accumulated Departure from Long-Term Mean Growing Season Precip. at Swift Current, SK 1000 re 800 600 artu ep 400 e D 200 tiv 0 lau -200 mu -400 C -600 1886 1906 1926 1946 1966 1986 Year
Effect of Weather on SOC Accumulation (e.g., Swift Current, Saskatchewan) 600 1967 1976 1990 1999 400 eparture “Normal” precip. Below average Above average 200 precip. precip. ean Precip. 0 M-200 ulative D -400 Cum From 1966 1976 1986 1996 Year -1 1967 – 1976 1976 – 1990 1990 – 1999 613 ) 470 y-1 255 Ra 102 t 60 e I c 26 m 1 n o c f r d Fal Cont. S ea ep . O s t C e h i n ( k 0 g – h 1 a 5
Effect of Increased Residue Inputs (e.g., Indian Head, Saskatchewan) 40 a)/hg 38 (M ic C 36an y = 0.01x + 23.14 rg 34 R2 = 0.75 il Oo S 32ean M 30 500 600 700 800 900 1000 1100 1200 Mean Residue C inputs per rotation (kg/ha/yr)
Effect of Crop Type (Based on a 36 year study on a Brown Chernozem at Swift Current, Saskatchewan). F-W-W F-Ry-W W-Lent F-Flx-W Cont W C (Al systems O 300 291 267 267 S received N+P) S received N+P in )-1 200 179 ain yr -1 a al g 121 al g u h 100 n (kg an 0 ean M Measured
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 til age, 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 Til age (Paustian et al., 1997)
Effect of Cropping Frequency (on SOC in 0 – 20 cm depth) Sterling (Low Stratton (Medium Walsh (High PET) PET) PET) 0.4 Summit – a 0.2 h 0 g -0.2 (MC 0.4 Sideslope O 0.2 S ) 1 0 in -0.2 egn 0.4 Toeslope ah 0.2 C 0 -0.2 60 80 10 60 80 100 60 80 100 Cr 0 opping Frequency (%) (Changes after 10 years of no-til on 3 sites in Colorado which were in conventional til F – Crop during previous 50 60 years).
Summerfal ow Area- U.S. A. Northern Great Plains 30 n ha) illio 25 area (m w 20erfallo mum 15 S 1980 1985 1990 1995 2000 Year
Effect of Grassland Conversion (Amount of C sequestered in agricultural soils for various management practices). Practice Amount C sequestered Investigators (Range) (Mg C/ha/yr) Improved grassland 0.59 Conant et al., 2001 management (Canada/U.S.A.) 0.05 – 0.3 Lal, 2001 Converting cultivated 1.01 Conant et al., 2001 lands to grasslands Reduction of summer 0.05 – 0.4 Lal, 2001 fallow
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; general y 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 wil 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 rainfal 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 fal ow 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 fal ows 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 til age, mulch farming, improved fal ows, 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 rainfal (> 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 especial y 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, especial y 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 wil sequester C than to rely on measurements of absolute gains in soil C. Spatial variability makes this a chal enging 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 wil 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 wil likely be wil ing to adopt such practices as reduced til age, use crop rotations instead of monocultures, increase cropping frequency at the expense of bare fal ow in arid and semi-arid environments, grow forage crops on marginal land and make more efficient use of fertilizers by using soil test criteria, al of which are positive alternatives for reducing CO 2 emissions and increasing C sequestration.