Effects of Nitrogen Fertilization on Yield and Yield Components of Tropical Maize Cultivars

Six tropical maize cultivars were grown in Thailand on a reddish brown latosol under three nitrogen regimes, 0, 40 and 80 kg N/ha. With regard to biomass and economic yield several "cultivar by N fertilization response types" were discriminated. The low fertilization type was represented by an early and a late maturing cultivar, both yielded comparatively well without additional N and responded little to N fertilization. An opaque 2 cultivar and a commercial hybrid belonged to the high fertilization type, they had a very low yield without N and needed high N fertilization to produce a high yield. The other genotypes were of an intermediate type with comparatively high yields without N, a considerable increase in yield at 40 kg N/ha and some increase from 40 to 80 kg N/ha. Genotypic variability for the harvest index was high but values were at the usual low level of tropical cultivars. High fertilization types reacted to an additional N supply with a marked increase in kernel number/plant and little increase in kernel weight. The early maturing low fertilization type reacted quite the opposite way. All other genotypes predominantly increased kernel number from 0 to 40 kg N/ha and kernel weight from 40 to 80 kg N/ha.