Reproduced,
with permission, from:
Changes in planting and harvesting practices
Climate warming may allow farmers to plant earlier in the spring. Earlier planting could lessen the chances of damage from heat waves at critical stages of plant growth. Shifting the period when a crop's leaf area is largest so that it matches the months of maximum sunlight would increase growth rates. Earlier planting would also allow earlier harvesting because warmer temperatures speed up plant development. Earlier harvesting reduces the risks of late-season field losses. Earlier maturation may also allow grain crops to dry more completely in the field, eliminating or reducing the need for artificial drying.
Warmer springs imply a longer growing season. Early planting in combination with a longer season cultivar may allow farmers to increase yields by taking advantage of the longer season---provided that moisture is adequate and the risk of heat damage is not too great. For risk-averse producers, earlier planting combined with a shorter-season cultivar may give the best assurance of avoiding the large losses associated with hot summer temperatures. Planting a mix of cultivars with different maturation times could increase the probability that some portion of the crop is exposed to the most favorable climate during a growing season (93).
Planting seeds deeper in the soil and reducing planting densities (plants per acre) are two simple ways of evading drought stresses. Planting seeds deeper may give them access to more moisture, which would facilitate successful germination. Smaller plant populations reduce competition among plants for available soil moisture.
Tactics for conserving moisture
Several moisture-conserving practices have been used to combat drought and aridity (77, 94, 97) and may be useful in adjusting to climate change. Conservation tillage is the practice of leaving the residue of the previous season's crop on the surface of the field, rather than plowing it under the surface. Conservation tillage protects fields from water and wind erosion and can help retain moisture by reducing evaporation and increasing the infiltration of precipitation into the soil. Conservation tillage also decreases soil temperature. Furrow diking is the placing of small dikes across the furrows of the field to aid the capture of rainfall. Terracing, or contouring, can be used to more efficiently trap precipitation on sloped fields. However, the construction of terraces can be costly.
Crop substitution is potentially a way to conserve moisture. Some crops require less water and tolerate warm, dry weather conditions better than others. For example, wheat and sorghum are more tolerant of heat and dryness than is corn. Microclimate modification can be achieved through the use of shelterbelts, or windbreaks. Shelterbelt systems are linear configurations of trees or tall annuals surrounding one or more sides of agricultural fields.[1] They greatly reduce wind speed across the protected field, benefiting plant growth by reducing evaporative-moisture losses (77). They are particularly effective in windy regions that otherwise have little natural woody vegetation, but they are costly in terms of land use.
Irrigation scheduling is the practice of supplying crops with irrigation water only when they need it. It adjusts the timing of the irrigation and the amount of water to match actual field conditions. Irrigation scheduling requires sources of information about soil-moisture conditions and, when using ditch irrigation, close cooperation among farmers. A study of four Nebraska counties found that irrigation scheduling on center-pivot systems reduced irrigation-water use by 9 percent and saved farmers an average of $2.10/acre in pumping costs (8). Low-energy precision application (LEPA) is an adaptation of the center-pivot irrigation system; low-pressure application of water near ground level results in less water loss to evaporation. Trickle irrigation applies water as drops or trickles through pipes on or below the soil surface. These very efficient but high-cost irrigation systems are now in common use only for fruit crops and highly valued vegetable crops.
Increased irrigation
Increased irrigation is one obvious means of coping with drier conditions. However, inadequate water supplies and high costs will limit this option in some regions. Regions that are currently reaching the limit of existing irrigation-water supplies (e.g., the Southern Plains and California) will be unlikely to support additional irrigation-water use (35, 69). Irrigation may decline because of increased urban competition for water and because of possible reductions or seasonal changes in the timing of stream flows. Irrigated acreage may increase only in eastern regions, where water supplies are adequate. Under a climate change, irrigated acreage as a percentage of total cultivable land could increase by perhaps 3 percent in the eastern third of the United States (69). The trend toward increased irrigation in the eastern United States is already under way.
Equipment purchase and Increased farming Intensity
Climate change may cause the quantity and quality of production inputs to change. Several agricultural experts argue that climate change may encourage farmers to alter their investments in on-farm infrastructure in order to: 1) purchase equipment necessary to change cropping systems, 2) expand the size of operations in order to offset climate-induced yield reductions, and 3) enlarge storage facilities to provide a buffer against extreme events such as drought and pest and disease outbreaks (68). Others note that farmers make investments in apparently excess equipment capacity to better ensure that farm activity can be completed before a period of unfavorable weather (90). Intensification of farming in areas beneficially affected by climate can be a way to maintain overall farm yields.
Reduced farming intensity
If the frequency of poor yields increases, some farmers may reduce the amounts or quality of inputs to production (89). One example would be to make fewer passes over the field for cultivation in order to hold down energy costs. Allowing irrigated acreage to revert to dryland farming or grasslands may occur when water is short or when water delivery costs rise, as has already happened in the southern Ogalalla Aquifer (see box 6-G). Fallowing (holding land out of production for a year in order to accumulate sufficient soil moisture) is often a necessary practice in dryland wheat farming. In the extreme, acreage abandonment (including not harvesting planted acreage and converting to woodlands) can be the most effective cost-cutting response to an unfavorable climate (60). Successful adaptation from this perspective means finding the most profitable means of farming; it does not mean that past production levels are necessarily maintained.
Helping livestock adjust
Several tactics may be used to help livestock adjust to excessive heat (38). The temperature of animals' surroundings can be reduced by providing shade or partial shelters. Trees make the best shade because they provide protection from direct sunlight and beneficial cooling as moisture is transpired from leaves. During a 3-day heat wave in Chino Valley, California, in 1977, more than 700 dairy cattle died (38). Deaths in lots with adequate shade were almost 70 percent lower than those in lots where cattle had inadequate shade. Evaporative coolers that lower air temperature in animal shelters can be effective in limiting productivity losses under high temperature conditions (38). Animal wetting is an effective way to lower the surface temperature of animals. This can be accomplished with a sprinkler system controlled by a timer. Maintaining large feed reserves is another tactic that livestock farmers use to lower their risk of facing feed shortages during climate extremes (9).
Farm structure and marketing practices
Increasing the scale of farming operation may in some cases effectively reduce the variability in income and yields. Strategic specialization can be an advantage in a small number of safe crops(55). Efficient farming in the "safest" crop is certainly a frequent---and perhaps the best---defense against climate risk. On dryland farms in the Western Great Plains, where crop failures from drought occur regularly, farmers grow wheat or sorghum, using conservative and low-cost methods. To the east, where rainfall is more abundant, corn and soybeans are the dominant crops. Large-scale farming enterprises can hedge against localized climate risks by diversifying geographically, spreading their farm holdings across climate zones. In the face of increasing climate uncertainty, the value of crop diversification on individual farms through the addition of less-risky crops may increase. A 1985 survey of farmers in Florida and Alabama found that they deal with variable climate risk by keeping their operations diversified (9). The large variability from decade to decade in Illinois corn yields can be seen as an example of a response to climate change, and farmers there have responded to the perception of increasing climatic risks by diversifying.
Owners of citrus groves in north-central Florida adapt to the risks of winter freezes by diversifying their source of income more than do the citrus growers to the south, who face less risk (61). Corporate ownership or partnerships allow each investor to risk relatively little income. The fruit is often sold through vertically integrated cooperatives, rather than in on-the-spot markets, as in the south. This marketing practice allows for speedy processing of freeze-damaged fruit, a benefit that compensates for lower average prices. Changes in the structure of farm ownership and vertical integration through contractual marketing arrangements can be effective institutional ways to spread the risk inherent in farming.
SOURCES: W.E. Easterling, "Adapting United States Agriculture to Climate change," contractor report prepared for the Office of Technology Assessment, January 1993; Office of Technology Assessment, 1993.