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ACS 106: Introduction to Agriculture st Semester 2014 1 Lectures 3 -6: Climate and Agriculture Prof Shellemiah O Keya 30 th January 2014
References The Earth’s Environmental Woes: Is Agriculture Part of the Problem or Part of the Solution? Reported by Ellen Wilson Chapter 24: Global Warming changes the focus for Agriculture
References contd Gommes, R. 1993. Current climate and population constraints on world agriculture. In: Agricultural Dimensions of Global Climate Change. H. M. Kaiser and T. E. Drennen (eds. ). pp. 67 -86. Holmes, R. 1995. Arctic ice shows speed of climate 'flips'. New Scientist 145 (1967): 13. Houghton, J. T. , Meira Filho, L. G. , Bruce, J. , Lee, H. , Callander, B. A. , Haites, E. , Harris, N. and Maskell, K. (eds. ). 1995. Climate Change 1994. Radiative forcing of climate change; and an evaluation of the IPCC IS 92 emission scenarios. Cambridge University Press, Cambridge, New York, Melbourne.
References contd Kaiser, H. M. and Drennen T. E. (eds. ). 1993. Agricultural Dimensions of Global Climate Change. St. Lucie Press, Delray Beach, Florida. 311 p. Katz, R. W. and Brown, B. G. 1992. Extreme events in a changing climate: variability is more important than averages. Clim. Change 21: 289 -302. Keeling, C. D. , Whorf, T. P, Wahlen, M. and van der Plicht, J. 1995. Interannual extremes in the rate of rise of atmospheric carbon dioxide since 1980. Nature 375: 666 -670. Kukla, G. and Karl, T. R. 1993. Nighttime warming and the greenhouse effect. Envir. Sci. Technol. 27 (8): 14681474.
Learning objective Comprehend the close relationship between climate and agriculture Establish that climate change affects agriculture and vice versa Understand that adaptation to climate change is central in agriculture
Recapitulation of Lectures 1 - 3 Soils and Great/ Early Civilizations Great civilizations had good soils as one of their natural resources In Kenya the highest population density are in the counties with good/fertile soils Other examples of fertile soils The ancient dynasties of the Nile were made possible by food producing capacity of the fertile soils of the valley and associated irrigation system. Tigris and Euphrates rivers in Mesopotamia and Indus, Yangtse and Huang Ho rivers in India and China respectively represent inhabitants of flourishing civilization
Soils and Great Civilizations These fertile soils made possible stable and organized communities and even cities In contrast to nomadic, shifting societies associated upland soils with concomitant animal grazing Soils destruction or degradation or mismanagement was also associated with the downfall of some of these civilization that good soils had helped to build
Siol in perspective- Past and Present In the Euphrates and Tigris the elaborate irrigation and drainage systems were not maintained – resulting in accumulation of salts; Once the productive soils became barren and useless, the thriving civilizations vanished; The flourishing cities that had occupied these areas fell into ruins and the people migrated elsewhere; The ruins of Babylon in Syria is a living example; Thus people are dependent on soils and to an extent good soils are dependent on people.
Most people settle where the best soils are. . .
Kenya's Shrinking Land Base (UNDP 2008)
Soil and climate Soil formation is intrinsically linked to climate Soil formation is a function of: Climate + Vegetation+ Parent material +Topography + Time Climate has a dominant factor in the soils that you see
Agriculture and climate systems Agriculture systems : Climate system Crop agriculture, Cloudiness, wind, rain , evaporation Animal husbandry, Temperature Forestry and Fisheries can be defined as one of the systems, and climate the other. If these systems are treated independently, this would lead to an approach which is too fragmentary
Land mass show wide variety of climates Tropical rainforest – found particularly in the centre of the continent, and along the eastern coast of Madagascar. Humid sub-tropical – found in the south-west. Mediterranean – mostly on the north-west (Mediterranean) coast and in the south-east Savannah – found to the north and south where it replaces the rain forest. There are distinct wet and dry seasons.
Climate change-induced change in Aridity Index (P/PET) - productivity reduction Vicious circle 1931 -1960 Africa 1961 -1990 Land degradation Dry sub-humid 25 Mha Humid 3 Mha Semi arid 51 Mha Arid Hyper arid Hulme, M. et al. , Climate Research, 1992 1931 -1960 Aridity Index 1961 -2000 AI < 0. 05 < AI < 0. 20 < AI < 0. 50 id 0. 50 < AI < 0. 65 D um ry Humid AI > 0. 65 sub. H Dry Biodiversity loss Climate change Se hum sub Sicily Se Semiarid id mi h. Precipitation • u mi ari mid ari d = Aridity Index ~ d • Evapopotential productivity transpiration Humid Sciortino, M. et al. 2010 (submitted)
Vicious circle Land degradation Reduced carbon fixation and sequestration Global carbon stocks Reduced Soil erosion Droughts fires, floods Increased • frequency • intensity SOC in eroded soil oxidizes Increased emissions Climate change & increased CO 2 • Crop failure • Forage decline Reduced biological productivity of economic value • Precipitation change • Evapotranspiration Soil protection Degraded SOC depletion Loss of • nutrients • soil moisture Diversity of soil vegetation cover Reduced Biodiversity loss & agrodiversity failure Species differential • sensitivity to climate change increase • Soil moisutre • response to decrease elevated CO 2
Land mass and varying climate Steppe – away from the Equator, to the north and south, the savannah grades into drier steppe. Desert – little rainfall, and big daily differences between day and night temperatures. The Sahara in the north is the world’s biggest desert. Only three countries cover a greater area – Russia, Canada and China. The Kalahari in Southern Africa covers an area larger than France. Highland – largely found in the east, below the Horn of Africa. Marine – largely in the south-east.
Issue of climate Becoming more global. It is now widely held view that human activities can affect climate, one of the components of the environment. Climate in turn affects agriculture, the source of all food consumed by human beings and domestic animals. Climate may be changing, Human societies and agriculture development trends constraints climate
The changing agricultural environment THE CLIMATE 'COMPLEX Climate variability is likely to increase under global warming (Katz and Brown, 1992), The rate of change itself is extremely important Changes would be associated with dramatic effects Ocean waters and associated products Cause havoc to established national fishery activities Would make adaptation to climate change difficult Most agricultural planning would be extremely difficult.
AGRICULTURAL GREENHOUSE GASES Important greenhouse gases are: Carbon dioxide (CO 2), Methane (CH 4), Nitrous oxide (N 2 O), Troposphere ozone (O 3) and Chlorofluorocarbons (CFCs). Basic characteristics of the first three gases are given later The degree to which these greenhouse gases stem from agricultural sources is also important
Major sources of GHG Deforestation Wetland rice Ruminants Biomass burning Synthetic fertilizers Manures and animal excreta
The world agricultural context The following are significant trends for the near future: World production of cereals will continue to grow, Export of cereals will undergo a modest growth in demand; The livestock sector in developing countries will continue to grow; Root crops, tubers and plantains will retain their importance; Oil crops will undergo rapid growth in developing countries; most importantly, Many developing countries will become net agricultural importers.
Ecological and indirect climate effects Overall predictability of weather and climate would decrease, making the day-to-day and medium-term planning of farm operations more difficult; Loss of biodiversity from some of the most fragile environments, such as tropical forests and mangroves; Sea-level rise (40 cm in the coming 100 years) would submerge some valuable coastal agricultural land; Incidence of diseases and pests, especially alien ones, could increase
Ecological effects cont Present (agro) ecological zones could shift in some cases over hundreds of kilometers horizontally, and hundreds of meters attitudinally, With the hazard that some plants, especially trees, and animal species cannot follow in time, and that farming systems cannot adjust themselves in time; Higher temperatures would allow seasonally longer plant growth and crop growing in cool and mountainous areas, allowing in some cases increased cropping and production. In contrast, in already warm areas climate change can cause reduced productivity; The current imbalance of food production between cool and temperate regions and tropical and subtropical regions could worsen.
Plant physiological direct effects The greenhouse gases CH 4, N 2 O and chlorofluorocarbons (CFCs) have no known direct effects on plant physiological processes. They only change global temperature and are therefore not discussed further. Instead, concentration should be on the effects of increased CO 2 tropospheric O 3, increased UV-B through depleted stratospheric ozone, Increased temperatures and the associated intensification of the hydrological cycle. CARBON DIOXIDE
The CO 2 fertilization effect CO 2 is an essential plant 'nutrient', In addition to light, Suitable temperature, water and chemical elements such as N, P and K, and it is currently in short supply. Higher concentrations of atmospheric CO 2 due to increased use of fossil fuels, deforestation and biomass burning, can have a positive influence on photosynthesis (Figure 1. 2) Under optimal growing conditions of light, temperature, nutrient and moisture supply, biomass production can increase, especially of plants with C 3 photo-synthetic metabolism
The CO 2 anti-transpirant effect With increased atmospheric CO 2 the consumptive use of water becomes more efficient because of reduced transpiration This is induced by a contraction of plant stomata and/or a decrease in the number of stomata per unit leaf area. This restricts the escape of water vapour from the leaf more than it restricts photosynthesis
The CO 2 anti-transpirant effect (improved water-use efficiency WUE) With the same amount of available water, there could be more leaf area and biomass production by crops and natural vegetation. Plants could survive in areas hitherto too dry for their growth.
ULTRAVIOLET RADIATION Increased ultraviolet radiation (UV-B, between 280 and 320 nanometers), due to depletion of the stratospheric ozone layer, Mainly in the Antarctic region, may negatively affect terrestrial and aquatic photosynthesis and animal health. Over the last decade, a decrease of stratospheric ozone was observed at all latitudes (about 10% in winter, 0% during summer and intermediate values during spring and autumn). However, the 'Biological Action Factor' of UV-B can vary over several orders of magnitude with even slight changes in the amount and wavelength of UV-B.
Effect of increased UVR There are damaging effects of increasing UV-B on crops, animals and plankton growth. It has been reported that UV-B affects the ability of plankton organisms to control their vertical movements and to adjust to light levels; Reductions in yield of up to 10% have been measured at experimentally very high UV-B values, and would be particularly effective in plants where the CO 2 fertilization effect is strongest. On the other hand, UV-B increase could increase the amount of plant internal compounds that act against pests.
TROPOSPHERIC OZONE Tropospheric ozone originates about half from photochemical reactions involving nitrogen oxides (NOx), methane or carbon monoxide, and half by downward movement of stratospheric ozone. High ozone concentrations have toxic effects on both plant and animal life (German Bundestag, 1991; It is likely that ozone, in conjunction with other photooxidants, is contributing towards the 'new type of forest damage' observed in Europe and the United States In the tropics, tropospheric ozone concentrations are generally lower than at northern mid-latitudes. However, this does not apply to periods when biomass burning releases precursor substances for the photochemical formation of ozone.
TEMPERATURE Rising temperatures - now estimated to be 0. 2°C per decade, or 1 °C by 2040 Would diminish the yields of some crops, especially if night temperatures are increased the temperature increase since the mid-1940 s is mainly due to increasing night-time temperatures, While CO 2 -induced warming would result in an almost equally large rise in minimum and maximum temperatures
TEMPERATURE Higher temperatures could have a positive effect on growth of plants of the CAM type. They would also strengthen the CO 2 fertilization effect and the CO 2 anti-transpirant effect of C 3 and C 4 plants Higher night temperature may increase dark respiration of plants, diminishing net biomass production;
TEMPERATURE Higher night temperature may increase dark respiration of plants, diminishing net biomass production; Higher cold-season temperatures may lead to earlier ripening of annual crops, diminishing yield per crop, but would allow locally for the growth of more crops per year due to lengthening of the growing season. Winter kill of pests is likely to be reduced at high latitudes, resulting in greater crop losses and higher need for pest control; Higher temperatures will allow for more plant growth at high latitudes and altitudes.
What can be done in drylands? and likely to apply to non-drylands too Restoration Soil depleted Soil salinized Range degraded Afforestation Runoff harvesting • Builds soil • Halts erosion • Regulates water • Promotes forage • Provides firewood Transfer to patch cultivation -agroforestry Below-ground SOM Above-ground stand Arid dryland After 35 y - twice as much SOM as the adjacent non-forested, degraded land Increasing C Reducing Food stocks emissions poverty security
The hydrological cycle and soils The extra precipitation on land, if indeed including present sub humid to semi-arid areas, will increase plant growth in these areas, leading to an improved protection of the land surface and increased rain fed agricultural production; in already humid areas the extra rainfall may, however, impair adequate crop drying and storage;
The hydrological cycle and soils The extra precipitation predicted to occur in some regions provides possibilities for off-site extra storage in rivers, lakes and artificial reservoirs (on-farm or at sub catchment level) for the benefit of improved rural water supply and expanded or more intensive irrigated agriculture and inland fisheries: The effects on water resources and water apportioning of international river and lake basins can be very substantial, with political overtones
Other risks Increased temperatures may lead to more decomposition of soil organic matter; Increased plant growth due to the CO 2 fertilization effect may cause other plant nutrients such as N and P to become in short supply; however, CO 2 increase would stimulate mycorrhizal activity (making soil phosphorus more easily available), and also biological nitrogen fixation (whether or not symbiotic). Through increased root growth there would be extra weathering of the substratum, hence a fresh supply of potassium and micronutrients;
Other risks The CO 2 fertilization effect would produce more litter of higher C/N ratio, hence more organic matter for incorporation into the soil as humus; litter with high C/N decomposes slowly and this can act as a negative feedback on nutrient availability; the 'CO 2 anti-transpirant' effect would stimulate plant growth in dryland areas, and more soil protection against erosion and lower topsoil temperatures, leading to an 'antidesertification effect'.
Conclusions Global climate change, if it occurs, will definitely affect agriculture. Most mechanisms, and two-way interactions between agriculture and climate, are known, even if not always well understood. It is evident that the relationship between climate change and agriculture is still very much a matter of conjecture with many uncertainties it remains largely a conundrum.
Conclusions Major uncertainties affect both the Global Circulation Models (GCMs) and the response of agriculture, as illustrated by differences among models, especially as regards effects at the national and sub regional levels. In addition, many of the models do not take into consideration CO 2 fertilization and improved wateruse efficiency, the effect of cloud cover (on both climate and photosynthesis), or the transient nature of climate change.
Conclusions It is also worth remembering that enormous knowledge gaps still affect the carbon cycle (with a missing sink of about 2 Gt of carbon), the factors behind the recent near-stabilization of the atmospheric methane concentrations or the unexplained reduced rate of CO 2 increase in recent years, the effect of volcanic eruptions (such as the recent Pinatubo eruption), the effect of any increased cloudiness, etc.
Questions for revision 1. Describe with appropriate examples the uses of soils: a) in agricultural production b) Non agricultural activities 2. Explain briefly why soil information is important for a country’s development. 3. What is land degradation? 4. State five sources of green house gases 5. State five land qualities that constrain agriculture 6. Discuss the general issues of climate change on agriculture
Questions cont 7. What is CO 2 Fertilization effect? 8. Discuss the effect of increased UVR on: a) crops, b) animals, c) tropospheric ozone, d) rising temperatures 9. Discuss the ecological and indirect climate change effect on agriculture and the environment. 9. Discuss the principal types of land degradation. 10. During the last 50 years since attaining independence, discuss what did not work well in land management
CO 2 CH 4 N 2 O Atmospheric lifetime (yr) 120 14. 5 120 Direct GWP 1 1 24. 5 2 320 Pre-industrial concentration 3 280 ppmv 0. 8 ppmv 288 ppbv Present-day levels 360 ppmv 1. 72 ppmv 310 ppbv Current annual increase (%) 0. 5 0. 9 0. 25 Major agricultural sources 4 deforestation - wetland rice - ruminants - synthetic N fertilizers - animal excreta - biomass burning - biological N fixation Percentage of global source stemming from agriculture 30 40 25 Predicted change 19902020 - + +
Table 1. 3. Growth rates between 1961 and 1990 in agricultural sectors responsible for greenhouse gas emissions (from FAO, 1990). Europe and Asia do not include the former USSR. Domestic ruminant numbers were computed as the sum of cattle, sheep, goats, camels and buffaloes Continent 1961 -1990 exponential growth rate (%) Ruminant numbers Forested area Rice area Fertilizer consumption Africa 1. 29 -0. 43 2. 23 6. 21 N and C America -0. 07 -0. 02 1. 50 3. 29 S. America 1. 29 -0. 49 1. 65 9. 15 Asia 1. 18 -0. 59 0. 62 9. 54 Europe 0. 33 0. 25 0. 78 2. 75 Oceania 0. 07 -1. 15 5. 88 1. 25 World 0. 90 -0. 26 0. 74 5. 35
Figure 1. 2. Schematic effect of CO 2 concentrations on C 3 and C 4 plants (after Wolfe and Erickson, 1993). The main mechanism of CO 2 fertilization is that it depresses photo-respiration, more so in C 3 than in C 4 plants
Box 1. 2. Some mechanisms likely to affect biomass production under global change conditions. Note that the ratio between economic yield (e. g. , grain, fibre) and biomass may change relative to current conditions ETP: Evapotranspiration potential WHC: Soil water holding capacity ETA: Actual evapotranspiration OM: Organic matter WUE: Water-use efficiency LAI: Leaf area index The heavy line indicates a hypothetical link between increased humidity and cloudiness.
1985: Global Flood Archive – Dartmouth Observatory