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°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 (0×), normal (1×), twice normal (2×), and artificial (polypropylene) residue (AR1×)], 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 NO 3 –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 1× and AR1× 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 NO 3 –N production and a similar difference in mean corn N requirement at the 0× and 1× 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.