Studies have indicated that, by maintaining relatively high solution culture or soil NH+4/NO-3 ratios during the reproductive growth stage, certain corn (Zea mays L.) genotypes have a higher yield potential. Unfortunately, few data on soil NH+4 and NO-3 levels have been reported. A 3-yr field experiment was conducted in northeastern Kansas in 1987, 1988, and 1989 to evaluate the effects of time and form of applied N on fertilizer band NH+4/NO-3 ratios and on the N nutrition, dry-matter accumulation, and grain yield of two corn hybrids. Urea, urea-NH4NO3, urea plus Ca(NO3)2, NH4NO3, and Ca(NO3)2 solutions having NH+4/NO-3 ratios of 1:0, 3:1, 1:1, 1:1, and 0:1, respectively, were used at equivalent N rates. The nitrification inhibitors, nitrapyrin [2-chloro-6-(trichloromethyl) pyridine] and dicyandiamide, as well as two-way and three-way timing of application schemes were used to maintain N as NH+4. Split applications of ammoniacal N with a nitrification inhibitor were effective in maintaining elevated soil NH+4 concentrations from planting through early grain fill. In 1988 only, grain yield was increased slightly (3–9% higher) when corn was fertilized with ammoniacal N compared with NO-3 only. Overall, manipulation of soil NH+4/NO-3ratios had few effects on corn development or yield.
Contribution no. 91-381-J from the Kansas Agric. Exp. Stn. This research was supported by the Fluid Fertilizer Foundation and the Tennessee Valley Authority.