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NITROGEN MANAGEMENT

Corn Residue and Nitrogen Source Effects on Nitrogen Availability in No-Till Corn

Dep. of Soil Sci., 1525 Observatory Dr., Univ. of Wisconsin, Madison, WI 53706-1299. Research supported by the Wisconsin Fertilizer Research Program, the Univ. of Wisconsin Nonpoint Pollution and Demonstration Project, and the College of Agric. and Life Sci., Univ. of Wisconsin, Madison

^* Corresponding author (andraski{at}wisc.edu).

Effective N management practices are needed in high residue corn (Zea mays L.) production systems to enhance N fertilizer efficiency and avoid yield reductions due to inadequate N supplies. This 4-yr study was conducted on a well-drained silt loam soil in southern Wisconsin (43°17' N, 89°22' E) to determine the effects of corn residue cover amounts on soil and residue N supplying capability, the effectiveness of several surface-applied N fertilizers, and the relative importance of mechanisms potentially contributing to reduced N efficiency in no-till corn systems. Treatments consisted of corn residue level [none (0x), normal (1x), twice normal (2x), and artificial (polypropylene) residue (AR1x)], N fertilizer source (ammonium nitrate, urea, and urea–ammonium nitrate solution), and N rate (0–225 kg N ha–1 in 45-kg increments). Increasing residue levels lowered soil temperatures and early season soil NO₃–N production, and reduced corn grain yields without applied N. Ammonia losses reduced the effectiveness of urea-containing fertilizers but did not completely explain the observed N source differences. Nitrogen source effects were similar at all residue levels, suggesting that added N can overcome yield reductions at high residue levels. Yields, N mineralization, and soil temperature were similar in the 1x and AR1x residue treatments, indicating that soil temperature rather than N immobilization is the main contributor to decreased yields at higher residue levels. Differences in early season soil NO₃–N production and a similar difference in mean corn N requirement at the 0x and 1x residue levels, suggest that applying about 30 kg ha–1 of extra N will provide yield benefits in some years in no-till corn residue systems.

Abbreviations: AN, ammonium nitrate • ANF, additional nitrogen fertilizer • N_PS-PP, change in soil profile (0–90 cm) NO₃–N content between preplant and pre-sidedress sampling times • PNR, plateau nitrogen fertilizer rate • UAN, urea–ammonium nitrate • UANr, UAN plus simulated rainfall • 0x, corn residue removed • 1x, normal corn residue • 2x, twice-normal corn residue • AR1x, artificial residue at the 1x level

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Received for publication January 28, 2008.