Growth, development and delay of leaf senescence in pot-grown sunflower (Helianthus annuus L.): sources and rates of nitrogen

摘要

> size="2" face="Verdana, Arial, Helvetica, sans-serif">Sunflower is the fourth oil grain crop grown worldwide and some genotypes are used with ornamental purpose as cut and pot-grown flower. The objective of this study was to evaluate the effect of different sources and rates of nitrogen on some growth and developmental parameters, and on the delay of leaf senescence in pot-grown sunflower. An experiment was carried out inside a greenhouse in Santa Maria, RS, Brazil. Treatments were: urea, ammonium nitrate and calcium nitrate at rates of 0, 50, 100 and 150mg L-1 of N in the fertigation solution, with two weekly applications. The experiment was a two-factorial (sources and rates of N) in a completely randomized design with six replications. Each replication was a number 15 pot (1.5L, 15cm height) with one plant/pot. The variables analyzed were: final leaf number, final plant height, percentage of senescent leaves at selling stage and at the end of vase life, total leaf area per plant, phyllochron, and the thermal time from emergency to visible bud and from emergency to selling stage. The N source influences leaf area of pot-grown sunflower, with urea being recommend for higher leaf growth. The rate of around 100mg L-1 of N applied twice a week through fertigation promoted desirable characteristics for commercialization such as earliness and delay of leaf senescence.