Dryland Farming

Cultivated agriculture in areas where potential water use by plants exceeds growing season precipitation (Stewart et al., 2006). Water deficiency is the primary limitation to plant production in dryland farming. Special farming practices are required to counteract soil water deficiency during the growing season. A particular farming region is not considered dryland just because it depends exclusively on natural precipitation. It is only considered dryland if water is the primary factor limiting production. The central U.S. Corn Belt is typical of an area (Iowa, Illinois, etc.) that depends on natural precipitation, but does not practice dryland farming. This entry provides information about where dryland farming is practiced, provides a historical perspective, and describes necessary management strategies and sustainability issues.

Climate and Soil Zones

Dryland farming areas of North America are clustered within six geographical regions in the 17 Western states of the U.S. and the three prairie provinces of Canada. These areas provide classic examples of the soil and climate regions where dryland farming is the norm. Annual precipitation ranges from eight to 20 inches, but the percentage received as snow versus rainfall varies dramatically with latitude. North Dakota farmers, for example, are very concerned with trapping snow on their fields to conserve water, whereas Texas farmers receive so little snow that trapping it is not an issue. Precipitation effectiveness is greatly modified by the north-to-south temperature gradient. As temperature increases, the amount of water used by plants increases dramatically, and soil water storage potential decreases.

Soils in dryland farming areas possess characteristics that are primarily a function of the climates they formed in and the grass vegetation that was growing on them in their native state. Principal soils of the Great Plains are classified as Mollisols, Entisols, Aridisols, Vertisols, and Ustalfs. The Mollisols are the most extensive soils in dryland areas, and were formed under grass and forbs. They are characterized by dark-colored surface horizons high in organic matter and bases. Productivity (total plant material produced per year) of the soils always has been a function of the dry climate, long before planned management of the Plains began. Soils in dryland areas are very unweathered compared to soils in higher-rainfall areas. This results in high fertility, especially for plant essential elements like calcium, magnesium and potassium. Because these soils were developed under prairie grass vegetation, they also have a good organic matter supply in the surface soil. Unfortunately, the organic matter supply is easily depleted when the soils are placed under cultivation. Nitrogen is usually deficient after 30 years of cultivation, and farmers need to add fertilizer nitrogen to produce economic yields. In contrast, most of these soils are so well supplied with potassium that they will not need fertilizer potassium in the foreseeable future.

Historical Perspective

Early settlers of North America did not choose to farm in the areas where we now practice dryland farming because they believed these areas were deserts. To northern European immigrants, the prairies appeared barren and unproductive compared to their native countries. Farmers did not begin to realize until late in the nineteenth century that grain crops could be produced in these dry locations. The earliest pioneer farmers did not recognize the many hazards that accompanied dryland farming, and therefore often failed. Dryland farming research, funded primarily by federal agencies, found solutions for many of the problems in the early twentieth century, and today 60 percent of the wheat involved in international trade comes from the drylands of North America. Hard red spring and winter wheats are the mainstay of the Great Plains dryland areas, and the soft white wheats are produced in the Pacific Northwest. These areas are so productive that they are commonly referred to as the Bread Basket of North America because of the large amount of wheat produced in them.

Dryland agriculture is highly dependent on precipitation from both snow and rainfall, which makes water conservation very important. Each small increment of precipitation is critical to production, and profit is highly related to efficient use of precipitation. For example, in eastern Colorado an additional inch of water above the initial yield threshold results in an additional 4.5 bushels per acre of wheat (Greb et al., 1974). The unpredictable climatic conditions always pose an additional large threat to farmers. Records in eastern Colorado show, for example, that the probability of receiving 75 percent or less of the average annual precipitation occurs about 25 percent of the time (Greb, 1979). Economic fragility is an ever-present factor, and farmers must use cropping systems that can cope with this unpredictability. Dryland farms tend to have little enterprise diversity, with wheat being the primary cash crop. Whenever enterprise diversity is increased by producing crops other than wheat or by increasing livestock production, a more stable agricultural environment always results. Unfortunately, the cropping options are limited by plant adaptation and potential markets for the products.

Management Strategies

The change from the historically unstable agriculture to our modern productive systems started in the late 1930s. Duley and Russel (1939) were among the first to recognize that leaving crop residue cover on the soil surface during non-crop periods improved water capture, reduced evaporation, increased water retention, and decreased soil erosion. Although they did not recognize it at the time, their techniques also decreased soil stirring (cultivation), which indirectly had a positive effect on organic matter and nitrogen conservation. Water storage efficiency in summer fallow (14-month time between wheat crops) increased from 19 percent in the 1916 to 1930 period, to 33 percent with stubble mulch tillage in recent years. The additional water storage resulted from new production systems that maintained more residue cover on the soil surface with fewer tillage events. By 1970 improved water storage with no-till made it possible to shift from a two-year wheatfallow system to a three-year wheat-sorghum-fallow system in 16- to 19-inch rainfall zones.

Erosion potential in dryland farming areas has been very high because of the small amount of vegetation produced by dryland crops and because the crop rotations included large amounts of fallow time where soils have no vegetative cover. The most common cropping system is the wheat-fallow system where winter wheat is grown for 10 months and is then followed by a 14-month period before the next wheat crop is planted. During the fallow period the objective is to keep the fields weed-free and to conserve as much of the total precipitation as possible. In areas where spring wheat is grown, the crop period is only three months and the fallow is 21 months long.

The fallow period opens the door for very serious erosion. Prior to the 1970s, the weed control during fallow had to be accomplished with tillage, which destroyed the residue left from the previous crop. Six or seven tillage events during a 14-month fallow were not uncommon and bare soil was highly likely to be present for several months out of the 14- or 21-month total. In cases where crops are poor, the residue cover disappears even more quickly and erosion possibilities are heightened. In dryland farming areas agents of erosion, wind and water, are both prevalent. Erosion by water is potentially large, not because of long periods of rainfall, but because the dryland farming areas receive much of their summer rain as highly intense thunderstorms. During these storms, rainfall intensity is greater than the soil’s infiltration rate and water runoff is large. Thus, water erosion is a problem even in very dry places. Erosion by wind also can occur after the wheat crop is planted because during the seedling establishment period, the soil is not covered by the small plant seedlings.

Residue cover on the soil surface is extremely effective in controlling erosion. Just 50 percent cover by residue decreases soil erosion by 70 percent. Management techniques, ranging from cultivation timing to invention of sweep tillage machines, helped farmers control erosion by leaving more crop residue on the soil surface throughout the fallow period and on into the wheat seedling stage. Herbicidal weed control permits maintenance of even more residue cover because soils are not disturbed and residue is not destroyed by tillage machines, which further aids erosion control. Ultimate cover is obtained with no-till management where all weeds are controlled by herbicides and the soil is not disturbed except by the planting equipment. No-till provides the maximum control of soil erosion by wind or water. The reader will find an interesting, in-depth coverage of historical and modern water conservation practices in Unger et al., 2006.

Sustainability

Long-term viability and economic stability in dryland farming is achieved when farmers successfully integrate management factors ranging from water conservation to judicious fertilizer use. The ability to withstand wide swings in climatic variation is linked directly to minimizing input costs and maximizing water conservation. Dryland farmers usually are very conservative in terms of machinery purchases and machinery maintenance. Experience has taught them that sustainability results from keeping cash flow at a minimum for their operation, and this means as small a debt load as possible. Dryland farmers tend not to make short-term radical changes in their farming practices; they rely heavily on what they know sustained them in the past.

— G.A. Peterson

See also

• Agronomy; Conservation, Soil; Cropping Systems; Grain Farming; Tillage; Wheat Industry

References

• Duley, F.L. and J.C. Russel. “The Use of Crop Residues for Soil and Moisture Conservation.” Agronomy Journal 31 (1939): 703-709.
• Greb, B.W. Reducing Drought Effects on Croplands in the West-central Great Plains. USDA Information Bulletin. No. 420. Washington, DC: Government Printing Office, 1979.
• Greb, B.W., D.E. Smika, N.P. Woodruff, and C.J. Whitfield. “Summer Fallow in the Central Great Plains.” Summer Fallow in the Western United States. Conservation Research Report No. 17, pp. 51-84. Washington, DC: U.S. Department of Agriculture, Agricultural Research Service, 1974.
• Stewart, Bobby A., Parviz Koohafkan, and K. Ramamoorthy. “Dryland Defined and Its Importance in the World.” Pp. 1-26 in Dryland Agriculture, 2nd ed. Edited by Gary A. Peterson, Paul W. Unger, and William A. Payne. Madison, WI : American Society of Agronomy, Inc., 2006.
• Unger, Paul W., William A. Payne, and Gary A. Peterson. 2006. “Water conservation and efficient use.” Pp. 39-85 in Dryland Agriculture, 2nd ed. Edited by Gary A. Peterson, Paul W. Unger, and William A. Payne. Madison, WI : American Society of Agronomy, Inc., 2006.