ROLE OF NITROGEN FORM IN DETERMINING YIELD OF FIELD-GROWN MAIZE

Although the maize (Zea mays L.) plant can utilize either NH4-N or NO3-N, many hydroponic studies have shown that mixed-N nutrition (NH4 + NO3) can optimize growth and yield. Results from field studies have been more erratic, however, and may be influenced by genotype. A 2-yr field study was therefore conducted at Urbana, IL, to evaluate five maize genotypes (B73 x LH51, LH74 x LH51, LH74 x LH82, LHE136 X LH82, and LHE136 x LH123) for plant growth, nutrient content, grain yield, and canopy photosynthesis (P(s)) when N was supplied either as calcium nitrate (NO3 plots) or urea plus a nitrification inhibitor (mixed-N plots). Three of the five genotypes (B73 x LH51, LH74 x LH51, and LHE136 x LH82) increased grain yield (by 6-8%) when supplied with mixed N, compared with plants supplied with predominantly NO3. However, NO3-grown plants had equivalent or greater rates of canopy P(s) (almost-equal-to 5-10%) than mixed N plants, and the duration of P(s) was unaffected by N-form treatment at photosynthetic photon flux densities of 900 or 1800 mumol photon m-2 s-1. Furthermore, N-form treatment did not affect the duration of daily canopy P(s). Genotypes responsive to mixed N utilized distinct physiological strategies to achieve increased grain yields. For example, the genotype LHE 136 x LH82 increased the partitioning of dry matter to the grain, whereas LH74 x LH51 and B73 x LH51 increased total dry matter production. Mixed-N nutrition decreased the percentage of aborted kernels for the genotype B73 x LH51 and increased anthesis ovule number per earshoot for LH74 x LH82. Plants of the rive genotypes supplied with mixed N also increased whole-shoot N content at maturity (by 5-14%). Based on these data, we conclude that mixed-N nutrition can moderately increase grain yield and productivity of certain maize genotypes by altering dry matter accumulation and partitioning, earshoot and ovule development, and N accumulation.