Agronomic Responses of Corn Hybrids from Different Eras to Deficit and Adequate Levels of Water and Nitrogen

Triticum aestivum L.). These high application levels result in low N use efficiency (NUE), with estimates of Maintaining current high yields of corn (Zea mays L.) grown in NUE for world cereal grain production systems at only the USA poses an environmental threat due to continued overuse of 33% (Raun and Johnson, 1999). This represents a $15.9 water and N inputs. To reduce overreliance on inputs, future corn billion annual loss of fertilizer N. In addition to ecobreeding efforts should focus on improving tolerance of corn to water and N stresses, utilizing appropriate tolerance mechanisms. The objecnomic losses, N overapplication results in environmental tive of this study was to identify appropriate mechanisms by charactercontamination through nitrate N runoff or leaching, izing agronomic responses of 12 hybrids from three different eras making nitrate N the most common contaminant found (‘B73 Mo17’ from 1970s and three early 1990s and eight late 1990s in the surface and ground waters of the Corn Belt (CAST, Pioneer brand hybrids) to varying water and N supply. This was done 1999). Thus, while average corn yields have quadrupled by growing the hybrids under deficit and adequate levels of water over the last 50 yr from the combined use of improved (one-half and full evapotranspiration) and N (0 and 200 kg ha 1) in irrigation practices, greater N fertilizer use, and other techa field study and measuring yield and other agronomic variables. nological innovations (Christensen, 2002), maintaining While hybrid eras didn’t differ in response to varying water or N, current high yields of corn grown in the Great Plains individual hybrids varied in ability to maintain yield under water or of the USA poses an environmental threat due to continN stress. For example, under deficit water, ‘3417’ produced 27% more ued overuse of these inputs. yield than ‘3162’ while they yielded similarly under adequate water. To minimize input costs and environmental damage, Likewise, under deficit N, ‘34R07’ produced 42% more grain yield farmers will likely have to resort to producing corn with than ’33G27’ while they yielded similarly under adequate N. Agroless irrigation water and N fertilizer in the future. This nomic variables such as kernel number per unit area were highly correlated with grain yield (r 0.98), indicating hybrid ability to maximize will lead to increased levels of water and N stress imkernel number under varying water and N supply was critical to maxposed on the crop. To reduce overreliance on these imizing yield. Determining physiological mechanisms associated with inputs, future corn breeding efforts should focus on imability to maintain kernel number under stress should be a high priority proving tolerance of corn to water and N stresses, utilizof breeding programs. ing appropriate stress tolerance mechanisms. Characterizing the agronomic and physiological responses of differing corn hybrids to water and N stresses could help C grown under the semiarid conditions of the identify appropriate stress tolerance mechanisms for fuGreat Plains region of the USA requires suppleture corn breeding efforts. mental irrigation to attain maximum yields (Musick and Corn is relatively insensitive to water stress imposed Dusek, 1980). While irrigation increases corn yields, it during early vegetative growth stages because water dedepletes groundwater supplies (Clark et al., 2002) and mand is relatively low and plants can adapt to water stress is expensive, with fully irrigated corn requiring 500 to to reduce the impact of subsequent periods of water 600 mm of irrigation water and pumping costs reaching stress (Shaw, 1977). However, corn grain yield is sensiover $0.20 mm 1 ha 1 in some regions (Norwood and tive to water stress from just before silking though grain Dumler, 2002). Nitrogen availability represents another fill (Shaw, 1977; Hall et al., 1981; Westgate and Boyer, major factor limiting corn yields in the Great Plains, 1986), with the greatest degree of sensitivity occurring requiring the addition of large quantities of N fertilizers during the period of kernel number determination (Anto achieve current high yields (Marschner, 1995). Recent drade et al., 1999). Hall et al. (1981) indicated that kernel statistics (USDA-NASS, 2003) show for example that number was most sensitive to stress between tasseling corn grown in the USA receives around 5 million tons of and just after silking. N annually, over 2.5 times the amount applied to wheat Nitrogen stress reduces grain yield by delaying plant growth and development (Uhart and Andrade, 1995a) P.M. O’Neill, J.F. Shanahan, and J.S. Schepers, USDA-ARS, Lincoln, and reducing leaf area index, leaf area duration, and NE 68583; and B. Caldwell, Univ. of Nebraska, Lincoln, NE 68583. photosynthetic rate (Novoa and Loomis, 1981; Lemcoff Joint contribution of USDA-ARS and Agric. Res. Div. of the Univ. of and Loomis, 1986; Sinclair and Horie, 1989; Connor et Nebraska. Published as Journal Ser. no. 14623. Mention of commercial products and organizations in this article is solely to provide specific al., 1993). Uhart and Andrade (1995b) also showed that information. It does not constitute endorsement by USDA-ARS over grain yield and kernel number were reduced by N stress. other products and organizations not mentioned. The USDA-ARS These results from the literature imply that measureis an equal opportunity/affirmative action employer and all agency ment of agronomic variables like yield components may services are available without discrimination. Received 28 Apr. 2004. provide an indication or characterization of hybrid re*Corresponding author ([email protected]). sponse to stresses. Published in Agron. J. 96:1660–1667 (2004). © American Society of Agronomy 677 S. Segoe Rd., Madison, WI 53711 USA Abbreviations: NUE, nitrogen use efficiency.