Efficient Water Use in Dryland Cropping Systems in the Great Plains

those methods as they have been used from the Canadian Prairie Provinces to the southern Great Plains of Successful dryland crop production in the semiarid Great Plains the United States and the resultant effects on system of North America must make efficient use of precipitation that is often limited and erratic in spatial and temporal distribution. The purpose WUE. Additionally, differences in precipitation use effiof this paper is to review research on water use efficiency and precipitaciency (PUE) between cropping systems across the Great tion use efficiency (PUE) as affected by cropping system and managePlains region are identified. ment in the Great Plains. Water use efficiency and PUE increase with residue management practices that increase precipitation storage METHODS FOR INCREASING PSE, efficiency, soil surface alterations that reduce runoff, cropping seWUE, AND PUE quences that minimize fallow periods, and use of appropriate management practices for the selected crop. Precipitation use efficiency on Tillage Effects on PSE a mass-produced basis is highest for systems producing forage (14.5 kg ha 1 mm 1) and lowest for rotations with a high frequency of oilseed Precipitation storage efficiency increases as tillage incrops (4.2 kg ha 1 mm 1) or continuous small-grain production in the tensity is reduced during the summer fallow period. The southern plains (2.8 kg ha 1 mm 1). Precipitation use efficiency when increased soil water storage is a result of both maintaincalculated on a price-received basis ranges from $1.20 ha 1 mm 1 (for ing crop residues on the soil surface and reducing the an opportunity-cropped system with 4 of 5 yr in forage production number of times that moist soil is brought to the surface in the southern plains) to $0.30 ha 1 mm 1 {for a wheat (Triticum as tillage intensity is reduced. Data from winter wheat– aestivum L.)–grain sorghum [Sorghum bicolor (L.) Moench]–fallow fallow systems at North Platte, NE (Smika and Wicks, system in the southern plains}. Throughout the Great Plains region, 1968), and Sidney, MT (Tanaka and Aase, 1987), show PUE decreases with more southern latitudes for rotations of similar fallow PSE increasing from under 25% to around 40% makeup of cereals, pulses, oilseeds, and forages. Forage systems in as tillage intensity decreased from moldboard plow to the southern Great Plains appear to be highly efficient when PUE is computed on a price-received basis. In general across the Great no-till (Fig. 1, top). Data collected at Bushland, TX, folPlains, increasing intensity of cropping increases PUE on both a masslowed a similar trend with PSE increasing from 15% with produced basis and on a price-received basis. disk tillage to 35% with no-till (Unger and Wiese, 1979). The amount and orientation of crop residue affects PSE and soil water storage. Data from Sidney, MT; AkI the semiarid regions of the Great Plains of North ron, CO; and North Platte, NE; show PSE over the America, water is generally the most limiting factor 14-mo fallow period in a winter wheat–fallow system for crop production. Successful dryland agricultural sysincreasing from 15% to almost 35% as wheat residue tems in these areas must make efficient use of precipimass increased from 0 to 10 Mg ha 1 (Fig. 1, bottom; tation that is often limited and erratic in spatial and Greb et al., 1967). This is a result of increased shading of temporal distribution. The limited and erratic nature of the soil surface, cooler soil temperature, and decreased precipitation in this region led to the development of wind speed at the soil surface (Hatfield et al., 2001). cropping systems in which one crop was grown every Crop residues also increase precipitation infiltration by other year to allow soil water recharge during a fallow protecting the soil surface from raindrop impact and period, which then led to greater yield stability. Those subsequent crusting, thus reducing runoff. Russel (1939) cropping systems traditionally used tillage to control reported runoff in the April through September period weed growth during the fallow period. But tillage dein eastern Nebraska being reduced from 60 mm in a grades crop residues, making them less effective for disked field without surface crop residues to only a trace reducing evaporation and leaving the soil vulnerable to where stubble-mulch reduced tillage had been employed wind erosion. The development of herbicides for weed and where 9 Mg ha 1 of wheat residue remained on the control during the fallow period resulted in opportunisoil surface (Fig. 2, top). Baumhardt and Lascano (1996) ties for more frequent cropping. A number of methods showed cumulative infiltration increasing as amount of have been developed for increasing precipitation storstanding and flat wheat residue on the soil surface inage efficiency (PSE) and water use efficiency (WUE) creased up to 2.5 Mg ha 1 (Fig. 2, bottom). Other similar in these dryland systems. This paper reviews several of results illustrating the decreased runoff and increased infiltration and soil water storage resulting from reducing tillage intensity and increasing amount of surface crop D.C. Nielsen, USDA-ARS, Cent. Great Plains Res. Stn., 40335 County Rd. GG, Akron, CO 80720; P.W. Unger (retired), USDA-ARS, Conresidues were reviewed by Unger et al. (1994), Unger et serv. and Prod. Res. Lab., P.O. Drawer 10, Bushland, TX 79012; and al. (1998), and Unger and Stewart (1983). P.R. Miller, Dep. of Land Resour. and Environ. Sci., Montana State Univ., P.O. Box 173120, Bozeman, MT 59717-3120. Received 6 Jan. Abbreviations: PSE, precipitation storage efficiency; PUE, precipita2004. *Corresponding author ([email protected]). tion use efficiency based on crop dry matter or seed yield per millimeter of precipitation received; PUE$, precipitation use efficiency Published in Agron. J. 97:364–372 (2005). © American Society of Agronomy based on dollars returned per millimeter of precipitation received; WUE, water use efficiency. 677 S. Segoe Rd., Madison, WI 53711 USA