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Role of Nitrogen Form in Determining Yield of Field-Grown Maize

Dep. of Agriculture, Illinois State Univ., Normal, IL 61761
Dep. of Agronomy, 1102 S. Goodwin Ave., Univ. of Illinois, Urbana, IL 61801

^* Corresponding author.

Although the maize (Zea mays L.) plant can utilize either NH₄N or NO₃N, 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 (P₅) 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 68%) when supplied with mixed N, compared with plants supplied with predominantly NO₃. However, NO₃-grown plants had equivalent or greater rates of canopy P₅ (510%) than mixed N plants, and the duration of P₅ was unaffected by N-form treatment at photosynthetic photon flux densities of 900 or 1800 µmol photon m^–2 s^–1. Furthermore, N-form treatment did not affect the duration of daily canopy P₅. Genotypes responsive to mixed N utilized distinct physiological strategies to achieve increased grain yields. For example, the genotype LHE136 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 five genotypes supplied with mixed N also increased whole-shoot N content at maturity (by 514%). 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.

Received for publication July 19, 1991.