Corn residue and nitrogen source effects on nitrogen availability in no-till corn

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 degrees 17' N, 89 degrees 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 andARIx 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 Ox 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.