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Prolificacy and N Fertilizer Effects on Yield and N Utilization in Maize¹

Interest in the N utilization efficiency of different maize [Zea mays L.] hybrids has increased due to N pollution in the environment and the cost of N fertilizer. This two-year field study on a Typic Plinthic Paleudult compared the responses of prolific and semi-prolific corn genotypes to N fertilization by measuring yield, harvest index, and N utilization efficiency. Four prolific and four semi-prolific genotypes were grown with 56, 112, 168, and 224 kg N ha^–1. Plants were sampled during grain fill, separated into leaves, stalks, and ears, and analyzed for N concentration. The prolific genotypes maintained a greater N utilization efficiency (grain weight/total plant N) than the semi-prolific genotypes at all N fertility levels and showed a greater decrease in N utilization efficiency as N fertilization was increased. The prolific genotypes partitioned a larger proportion of plant N to the grain at all N fertility levels, apparently by increasing N remobilization. The semi-prolific genotypes responded to increased N fertility by increasing the ear number per plant, grain N content and grain yield. As N fertility increased, the semiprolific genotypes increased the proportion of dry matter partitioned to grain, corresponding to increased ear number. These results indicate that the ability of a corn genotype to increase grain yield in response to N fertility was not necessarily indicative of greater N utilization efficiency. Genetic selection for prolificacy under low N fertility may lead to identification of genotypes with more efficient N utilization ability.

Key Words: Ear number • N utilization efficiency • Partitioning • Remobilization

² Former graduate student, now soil scientist, USDA-ARS; professor of soil science; professor of genetics, North Carolina State Univ., Raleigh.

Received for publication March 12, 1984.