Agr50174 63..71

A no-till (NT) production system has potential to reduce soil erosion, fossil fuel consumption, and greenhouse gas emissions compared with a conventional till (CT) system. Nitrogen fertilization (four to six N rates) and tillage system (CT and NT) effects on irrigated, continuous corn (Zea mays L.) yields were evaluated for 5 yr on a clay loam soil to determine the viability of the NT system and N needs for optimum yield. Corn in both NT and CT systems responded similarly to available N supply. Grain yields were significantly increased by N fertilization in both tillage systems, with a 16% higher average maximum yield in the CT than in the NT system. Grain yields were near maximum with an available N (soil 1 fertilizer N) level of 276 and 268 kg N ha in the CT and NT systems, respectively. Nitrogen fertilizer use efficiency (NFUE) averaged 43% over N rates and years for both systems. Total N required to produce 1 Mg of grain at maximum yield averaged 19 and 20 kg N Mg grain for the CT and NT systems, respectively. Corn residue increased with increasing N rate with no difference in residue production between tillage systems. The lower grain yield with NT probably resulted from the slow early spring development and delayed tasseling compared with the CT system as a result of cooler spring soil temperatures in the NT system. No-till, irrigated, continuous corn production has potential for replacing CT systems in the central Great Plains area, but with reduced yield potential. Current N fertilizer recommendations for CT corn based on yield goal may need to be modified for NT to account for the lower yield potential and slightly higher N requirement. IRRIGATED FARMERS often use intensive tillage practices, particularly the moldboard plow, to manage the large quantity of crop residue returned to the soil surface when preparing a seedbed for the next crop. As a result of the numerous tillage operations, most of the crop residue is incorporated into the soil. With very little crop residue remaining on the soil surface, the soil is subject to wind and water erosion. Conversion from an intensively tilled irrigated crop production system to a conservation tillage system, like NT, would reduce the potential for soil erosion and loss of soil organic matter (Lal, 2004). Lal (2004) points out the need to use conservation tillage systems on croplands to enhance soil organic carbon (SOC) storage and reduce total greenhouse gas emissions from agricultural lands. Limited information is available on use of NT systems on irrigated lands in the semiarid central Great Plains (Cahoon et al., 1999; Sims et al., 1998). Data available from the more humid Western Corn Belt and eastern Nebraska suggest that NT systems may produce lower grain yields than CT systems (Wilhelm and Wortmann, 2004; Vetsch and Randall, 2002, 2004; Sims et al., 1998). Research suggests that cooler soil temperatures at planting time inNT systems delay early crop development and final yield (Sims et al., 1998; Swan et al., 1987). Sims et al. (1998) suggested that preplant tillage may be necessary to optimize grain yield when spring soil temperatures are cool on fine-textured soils. Sims et al. (1998) reported lower continuous corn yields with NT at low N rates compared with CT under sprinkler irrigation but equal yields at high N rates. Research from more humid areas suggests that the delay in early crop development with NT had no detrimental effect on final crop yield (Mehdi et al., 1999; Wolfe and Eckert, 1999). Cahoon et al. (1999) reported higher yields and greater economic returns when using conservation tillage on irrigated continuous corn. Smart and Bradford (1999) also reported greater economic returns from NT than from a CT corn production system. Tolk et al. (1999) suggested that conservation tillage systems that maintain crop residues on the soil surface reduce evaporation and conserve water for crop growth and production, making more efficient use of the limited water supplies in the Great Plains. Todd et al. (1991) also demonstrated the benefit of surface mulch in reducing evapotranspiration in irrigated corn. Halvorson et al. (2000) reported that plow tillage under furrow irrigation resulted in the loss of soil organic matter in the northern Great Plains, but the loss was less with a high level of N fertility. Under dryland production in eastern Colorado, Halvorson et al. (1999) showed that increasing N fertility level increased crop residue production, which resulted in greater soil organic matter. In an irrigated continuous corn production system, a large quantity of crop residue is produced. In a NT system, this residue is not incorporated with the soil, which slows the decomposition rate of the residue and release of residue N and other nutrients to the following crop. This may result in greater N requirements to attain equal grain yields for the NT system compared with the CT production system (Sims et al., 1998), at least for the first few years after converting to NT. Farmers in the South Platte River Valley in northeastern Colorado produce alfalfa (Medicago sativa L.), corn, winter wheat (Triticum aestivum L.), barley (Hordeum distichon L.), and dry bean (Phaseolus vulgaris L.) using predominantly intensive tillage (including the moldboard plow) to prepare a seedbed. Soil erosion A.D. Halvorson, C.A. Reule, and W.C. Bausch, USDA-ARS, 2150 Cent. Ave., Bldg. D, Suite 100, Fort Collins, CO 80526; A.R. Mosier, Agric. and Biol. Eng. Dep., Univ. of Florida, 281 Frazier Rogers Bldg., Museum Rd., P.O. Box 110570, Gainesville, FL 32611. Contribution from USDA-ARS. The USDA offers its programs to all eligible persons regardless of race, color, age, sex, or national origin, and is an equal opportunity employer. Received 10 June 2005. *Corresponding author ([email protected]). Published in Agron. J. 98:63–71 (2006).