Climate Change 2001: Working Group II: Impacts, Adaptation and Vulnerability

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13.3.4. Agriculture

To avoid or at least reduce negative effects and exploit possible positive effects, several economic and agronomic adaptation strategies for agriculture have been suggested. Economic strategies are intended to render the agricultural costs of climate change small by comparison with overall expansion of agricultural products. Agronomic strategies intend to offset the loss of productivity caused by climate change, either partially or completely. Agronomic strategies include short-term adjustments and long-term adaptations.

13.3.4.1. Short-Term Adjustments

Short-term adjustments to climate change are efforts to optimize production with major system changes. They are autonomous in the sense that no other sectors (e.g., policy, research) are needed for their development and implementation. Thus, short-term adjustment can be considered the first defense tool against climate change. A large range of such adjustments have been reported, including:

• Changes in planting dates and cultivars: For spring crops, climate warming will allow earlier planting or sowing than at present. Crops that are planted earlier are more likely to have already matured when extreme high temperatures, such as in the middle of summer, can cause injury. Earlier planting in spring increases the length of the growing season; thus, earlier planting and use of long-season cultivars will increase yield potential, provided moisture is adequate and the risk of heat damage is low. Otherwise, earlier planting combined with a short-season cultivar would give the best assurance of avoiding heat and water stresses. Deeper planting of seeds also will contribute to making seed germination more likely. For winter crops (i.e., cereals), this approach may cause problems because their cycle length often is linked with cold temperature requirements (vernalization) that may not be completely fulfilled during warmer winters. Late cultivars also may not be able to escape heat and drought risks in the summer. Winter cereals must have a specific growth stage before the onset of winter to ensure winter survival, and they often are sown when temperatures approach the time when vernalization is most effective (Harrison and Butterfield, 1996). This may mean later sowings in northern Europe under climatic warming.
• Changes in external inputs: External inputs are used to optimize production of crops in terms of productivity and profitability. The use of fertilizers generally is adjusted to fit the removal of nutrients by the crop and any losses of nutrients that may occur during or between growing seasons. A change in yield level therefore, all other things being equal, will imply a corresponding change in fertilizer inputs. Projected increases in atmospheric CO₂ concentration will cause a large nitrogen uptake by the crop and thus larger fertilizer applications. On the other hand, climatic constraints on yields may lead to less demand for fertilizers. Changes in climate also may cause larger (or smaller) losses of nitrogen through leaching or gaseous losses. This also may lead to changes in the demand for fertilizer. Global warming will lead to a higher incidence of weeds, pests, and diseases in many areas and thus to potentially increased use of chemical control measures (e.g., pesticides). These inputs can be kept low through adoption of integrated pest management systems, which adjust control measures to the observed problem and also take a range of influencing factors (including weather) into account. Current fertilizer and pesticide practices are based partly on models and partly on empirical functions obtained in field experiments. These models and functions are updated regularly with new experimental evidence. This process probably will capture the response of changes in the environment through CO₂ and climate. It is important, however, that agricultural researchers and advisors are aware of the possible impact of global change on the use of external inputs, so that older empirical data are used with proper caution.
• Practices to conserve moisture: Several water-conserving practices are commonly used to combat drought. These also may be used to reduce climate change impacts (Easterling, 1996). Such practices include conservation tillage and irrigation management. Conservation tillage (the practice of leaving some of the previous season’s crop residues on the soil surface) may protect the soil from wind and water erosion and retain moisture by reducing evaporation and increasing infiltration of precipitation into the soil. Irrigation management can be used to improve considerably the utilization of applied water through proper timing of the amount of water distributed. For example, with irrigation scheduling practices, water is applied only when the crop needs it. This tunes the proper timing and amount of water to actual field conditions, allowing a reduction in water use as well as the cost of production.

Table 13-7: Land management options to mitigate impact of climate change on soils.
Function	Impact	Management/Adaptation Options
Land production	- Salinization - Peat wastage - Acidification - Erosion - Compaction - Soil biodiversity	- Improved technology for application, better water quality, better water scheduling - No drainage of lowland peat soils - Soil pH management - Soil conservation techniques (expand) - Better timing of field operation, use of new tillage equipment - ???
Land regulation	- Soil water - Soil organic matter - Soil nutrients - Polluting chemicals - Soil temperature - Soil material resources	- Irrigation (with improved technology and scheduling) - Use of manures, reduced tillage, improved farming system methods, crop rotation management - Sustainable use of fertilizers/manures, crop rotation management - Limits on use of polluting chemicals, clean-up of contaminated land - Mulching - No adaptation possible
Land carrier	- Water movement and soil structure - Nitrate leaching - Volatilization - Carbon dioxide fluxes - Methane fluxes - Nitrous oxide fluxes	- Management of vertisols(?), timing of manure and sewage sludge applications - Change in fertilizer application rates, precision farming, crop selection (i.e., with different N requirements), breeding nitrogen-fixing crops, breeding crops to improve N-use efficiency (e.g., lower requirements, more efficient uptake), irrigation management, soil pH management, nitrification inhibitors, release rates (e.g., slow or timed release, coatings to limit or retard water solubility), improved fertilizer placement and timing (e.g., band placement, foliar applications), application placement (e.g., slurry injection), application timing, application amounts (e.g., controlled rate systems) - See management options appropriate to reduce nitrate leaching - Land-use change for carbon sequestration - Increased sink through fertilizer management - See management options appropriate to reduce nitrate leaching
Land information	- Historical record	- Conserve intact soil profiles and representative reference sites
Land consumption	- Shrink/swell damage	- Underpinning of building foundations, insure differently (e.g., location restrictions)