Leaf area profile of two sunflower cultivars under different rates and timing of nitrogen application

Abstract

Nitrogen applied at different rates or timing affects the canopy leaf area and leaf expansion varies according to its position through the profile. N application in a field experiment with two sunflower hybrids affected the leaf area at different positions of the plant: leaves at the middle of the canopy expanded more as more nitrogen was available. The bottom leaves changed little in size, either by different N rates or timing. Early nitrogen applications, as well as higher N rates, resulted in more leaf expansion in the central part of the canopy, with decreasing effects as application is delayed or N decreased. The hybrid DK 180 had more total leaf number and more leaves in the central-upper part of the canopy, which responded more effectively to the treatments applied.