Hydroponic studies on maize (Zea mays L.) have shown productivity to be greater when maize was supplied with mixed nitrogen, however, the benefits of mixed N nutrition under field conditions have been difficult to evaluate. This study was initiated to: (i) determine the effect of rate of point injected N and nitrapyrin (NI) on growth, yield and yield components of maize grown in soybean-corn (SB-C) and corn-corn (C-C) rotations, (ii) determine if a mixed soil N source may alleviate all or part of the inherent yield reduction caused by maize grown in C-C rotation, and (iii) determine if different hybrids grown in rotation respond similarly to mixed soil nitrogen sources;Three field experiments were conducted in 1990, 1991, and 1992 in C-C and SB-C rotations and with soil potassium (K) variables. Adequate N fertilizer for the corn was applied preplant. Rates of urea ammonium nitrate (UAN) solution and NI were point injected in a factorial combination at V4, V6, or V8 stages of corn development to vary ammonium ion content in the soil. Soil samples were used to monitor soil NH[subscript]4-N and NO[subscript]3-N concentrations;Grain yield of corn was 15 to 26% greater and the yield components seed mass and seeds plant[superscript]-1 were up to 15 and 13% greater for high K fertility compared with low K fertility, respectively. Treatment with UAN at V4 increased seeds plant[superscript]-1 by 4.5% compared to V6 or V8, and addition of 90 kg N ha[superscript]-1 produced 4.8% more grain yield than 45 kg N ha[superscript]-1. Nitrapyrin maintained an enhanced NH[subscript]4-N supply up to 8-wk post application. Soil ammonium to nitrate ratios were as high as 3:1 with 3.6 L NI ha[superscript]-1 compared with no NI;Low K fertility contributed to reduced seed mass, fewer seeds plant[superscript]-1, and reduced yield compared to high K fertility. Point injected N increased seed mass and seed plant[superscript]-1, which contributed to increased grain yield. The negative effect of C-C rotation could not be reduced by an enhanced soil ammonium supply.