The Influence of N Rates on Maize Leaf Number and Senescence in Nigeria

Leaf senescence greatly affects photosynthetic capacity, dry matter production and allocation in plants. Death of leaves as a result of senescence ends or limits dry matter production and allocation in plants. If more leaves are retained on the plants by delaying senescence, dry matter production may be maintained for a longer period leading to higher grain yield. Since redistribution of nutrients like nitrogen is the major reason for leaf senescence, adequate supply of N may delay senescence. Field experiments were therefore conducted in 1996 and 1998 in Mokwa (in the Southern Guinea savanna of Nigeria) on a sandy-loam (Tropeptic Haplustox) to determine the effects of different N rates (0, 30, 60, 90 and 120 kg N ha 1) on leaf number per plant and leaf senescence of nine maize (Zea mays L.) varieties. The highest number of leaves per plant (20.5) at anthesis was obtained from the 120 kg N ha 1 in both seasons while the lowest percentage leaf senescence was obtained from 120 kg N ha 1 at all the sampled periods. The highest grain yield was also recorded at the 120 kg N ha 1 in both seasons. Varieties 8644-27 and TZLCOMP4C1 that had the highest grain yield also produced the highest number of leaves and lowest percentage leaf senescence. This shows that N rates increased leaf number and delayed leaf senescence. Maintaining more green leaves for a longer period through higher N application resulted in higher grain yield. Maize varieties that produce more leaves and maintain them longer may yield higher.