Corn responses to ammonium- and nitrate-nitrogen fertilization

Studies have indicated that, by maintaining relatively high solution culture or soil NH4+/NO3- ratio during the reproductive growth stage, certain corn (Zea mays L.) genotypes have a higher yield potential. Unfortunately, few data on soil NH4+ and NO3- levels have been reported. A 3-yr field experiment was conducted in northeastern Kansas in 1987, 1998, and 1989 to evaluate the effects of time and form of applied N on fertilizer band NH4+/NO3- ratios and on the N nutrition, dry-matter accumulation, and grain yield of two corn hybrids. Urea, urea-HH4NO3, urea plus CA(NO3)2, NH4NO3, and Ca(NO3)2 solutions having NH4+/NO3- 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 NH4+. Split application of ammoniacal N with a nitrification inhibitor were effective in maintaining elevated soil NH4+ 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 NO3- only. Overall, manipulation of soil NH4+/NO3- ratios had few effects on corn development or yield