NITROGEN MANAGEMENT Nitrogen Fertilization and Rotation Effects on No-Till Dryland Wheat Production

and Reule, 1994; Norwood, 2000; Peterson et al., 1993; Schlegel et al., 2002). No-till (NT) production systems, especially winter wheat (Triticum Dhuyvetter et al. (1996) reported that the more intenaestivum L.)–summer crop–fallow, have increased in the central Great sive cropping systems had higher profit potential than Plains, but few N fertility studies have been conducted with these systems. Therefore, winter wheat (W) response to N fertilization in wheat–fallow systems in the Great Plains. This finding two NT dryland crop rotations, wheat–corn (Zea mays L.)–fallow was supported by the economic analyses of intensive (WCF) and wheat–sorghum (Sorghum bicolor L.)–fallow (WSF), on dryland cropping systems in eastern Colorado (Kaan et a Platner loam (fine, smectitic, mesic Aridic Paleustoll) was evaluated al., 2002) and in south-central North Dakota (DeVuyst for 9 yr. Five N rates, 0, 28, 56, 84, and 112 kg N ha 1, were applied and Halvorson, 2004). Greater profit potential with into each rotation crop. Wheat biomass and grain yield response to N creasing cropping intensity and NT production systems fertilization varied with year but not with crop rotation, increasing has enhanced the adoption of these systems. with N application each year, with maximum yields being obtained Crop water use efficiency is improved with more inwith 84 kg N ha 1 over all years. Based on grain N removal, N fertilizer tensive cropping systems (Halvorson, 1990; Nielsen et use efficiency (NFUE) varied with N rate and year, averaging 86, 69, al., 2002; Norwood, 1999; Farahani et al., 1998). Nitro56, and 46% for the 28, 56, 84, and 112 kg ha 1 N rates, respectively. gen fertilization can improve water use efficiency, but Grain protein increased with increasing N rate. Precipitation use efficiency (PUE) increased with N addition, leveling off above 56 kg N high N fertilization rates can result in excess biomass ha 1. A soil plus fertilizer N level of 124 to 156 kg N ha 1 was sufficient production, which uses up stored soil water needed for to optimize winter wheat yields in most years in both rotations. Appligrain production (Nielsen and Halvorson, 1991). Therecation of more than 84 kg N ha 1 on this Platner loam soil, with a fore, it is important to balance N fertilization with availgravel layer below 120 cm soil depth, would more than likely increase able seasonal water supplies. the amount of NO3–N available for leaching and ground water contamMore intensive cropping systems using NT may reination. Wheat growers in the central Great Plains need to apply N quire higher rates of N fertilizer to maintain yield potento optimize dryland wheat yields and improve grain quality, but need tial due to increased crop N removal as well as compento avoid over-fertilization with N to minimize NO3–N leaching posate for N sequestration in crop residue and surface soil tential. due to lack of tillage. Few N fertility rate studies have been conducted in the central Great Plains under NT conditions to evaluate the response of winter wheat to I the central Great Plains region of the USA, use N application in more intensive NT cropping systems of reduced tillage and NT systems increased during (Halvorson and Reule, 1994; Kolberg et al., 1996; the 1990s. These tillage systems improved the storage Thompson and Whitney, 1998). Halvorson and Reule of precipitation in the soil profile compared with me(1994) reported spring barley (Hordeum vulgare L.) chanical tillage systems, allowing more intensive cropyields were optimized with the application of 67 kg N ping systems to be developed (Anderson et al., 1999; ha 1 each crop year in a NT annual cropping system on a Halvorson and Reule, 1994; Halvorson et al., 2002; Weld silt loam (fine, smectitic, mesic Aridic Argiustoll). McGee et al., 1997; Nielsen et al., 2002; Peterson et al., Thompson and Whitney (1998) reported that 67 kg N 1996). The dominant wheat–fallow system of farming ha 1 applied to each crop was sufficient to optimize is being slowly replaced with more intensive cropping wheat and sorghum yields on a silt loam soil in Kansas. systems, such as 3-yr WCF and WSF systems, 4-yr sysKolberg et al. (1996) reported no yield benefits to N tems (crop–crop–crop–fallow), and annual cropping sysapplications above 84 kg N ha 1 on dryland winter wheat tems with no fallow (Anderson et al., 1999; Halvorson in WCF and WSF rotations on two loam soils in eastern Colorado. A.D. Halvorson, USDA-ARS, 2150 Centre Ave, Bldg. D, Suite 100, The objective of this study was to evaluate the influFort Collins, CO 80526; D.C. Nielsen, USDA-ARS, Central Great ence of N fertilization rate and crop rotation (WCF and Plains Res. Stn., 40335 County Road GG, Akron, CO 80720; and WSF) on dryland winter wheat yields, NFUE, PUE, C.A. Reule, USDA-ARS, 2150 Centre Ave., Bldg. D, Suite 100, Fort Collins, CO 80526. Contribution from USDA-ARS. The U.S. Departand residual soil NO3–N using a NT production system ment of Agriculture offers its programs to all eligible persons regardon a Platner loam soil with a gravelly layer below the less of race, color, age, sex, or national origin, and is an equal opportu120-cm depth. nity employer. Received 18 Dec. 2003. *Corresponding author (ardell. [email protected]). Abbreviations: NFUE, nitrogen fertilizer use efficiency; NT, no-till; Published in Agron. J. 96:1196–1201 (2004).  American Society of Agronomy PUE, precipitation use efficiency; WCF, wheat–corn–fallow; WSF, wheat–sorghum–fallow. 677 S. Segoe Rd., Madison, WI 53711 USA