Effects of paclobutrazol and nitrogen fertilizer on the growth and yield of maize

In two field experiments conducted in 1991 and 1992 at Akure, Nigeria, 0-12 and 0-24 ml/l of the plant growth regulator, paclobutrazol, and 0, 75 and 150 kg N/ha were applied to maize in factorial combinations. Substantial vegetative growth occurred with increasing N rates in 1991 and this accelerated 50 % silking date. Paclobutrazol influenced maize growth at this stage only in 1992 when 12 and 24 ml/l depressed plant height and increased both stem girth and leaf number/plant. Higher paclobutrazol application rates decreased plant height at maturity in both years while, in 1991, 150 kg N/ha enhanced it, and also stem girth and shoot dry matter yield. In 1991, both ear and grain dry weight yield/m(2) increased with higher N rates while in 1992 4-24 ml/l paclobutrazol enhanced ear dry yield/m(2) compared with untreated maize. Both chlorophyll a and b in the ear leaf increased with higher rates of paclobutrazol and N fertilizer, except in 1992 when high leaf N tended to mask the effect of paclobutrazol. N fertilizer in 1991 enhanced the contents of N and Ca in the ear leaf while depressing P, compared with untreated maize.