The effect of irrigation regimes and pattern of nitrogen topdressing on yield and yield components of sunflower

In order to evaluate the effect of irrigation and pattern of nitrogen topdressing on yield and yield components of sunflower, an experiment was carried out in complete block design with split-plot arrangement in three replications during 2012 growing season. Irrigation regimes were allotted to main plots and nitrogen treatments were allotted to sub-plots. Irrigation regimes were consisted of: 1) moderate irrigation 2) water stress at V8 growth stage and 3) water stress at heading stage. The nitrogen treatments were consisted of: N1: 25% at sowing, 50% at V8, 25% at heading; N2: 50% at V8, 50% at heading; N3:50% sowing, 50% heading; the results showed that water stress at heading significantly decreased the head diameter and100-grains weight and non-significantly decreased the grains per head which was resulted to 15% lower grain yield comparing to the moderate irrigation. Under moderate irrigation, N3 treatment non-significantly increased the head diameter and biomass comparing to the N2 treatment by 9 and 16% respectively. Under water stress at V8, N3 treatment significantly increased the head diameter and biomass comparing to the N1 treatment by 12 and 29%, respectively. This result showed that choosing a suitable pattern of nitrogen top-dressing for attaining the maximum grain yield is more important when the plants are not suffering water stress or stress is occurred at early vegetative stage. But when the stress is occurred at early vegetative stage, then the pattern of nitrogen topdressing is not such important.