Degree Type


Date of Award


Degree Name

Doctor of Philosophy



First Advisor

I. C. Anderson


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.



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Bill Stuart Curran



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179 pages