Agronomic and physiological assessment of nitrogen use, uptake and acquisition in sunflower

A field experiment was conducted to study the effects of N fertilization on uptake, accumulation/remobilization, use efficiency and yield of sunflower grown in alluvial plains of northwestern India comprising four hybrids (PSH 996, PAC 3789, PSH 569 and SH 3322) and five N levels (Control, 40, 80, 100 and 120 kg N ha-1) in split-plot design with three replications. Increased N fertilizer rates significantly prompted sunflower yield only up to 100 kg N ha-1. Every additional kilogram of N taken up increased sunflower yield by 26 kg ha-1. Significant genetic variation for seed yield and NUE traits explicated PSH 569 as the efficient one at sub-optimal N application while PSH 996 outperformed others at N80, N100 and 120. Dry matter accumulation pattern revealed average harvest index of 30% with 29% of the biomass as stalk, 19% as leaf and 22% as thalamus. Temporal changes in N acquisition indicated most of the total N uptake upto 50% flowering while maximum remobilization takes place during reproductive phase. Significant correlation between N uptake and N use efficiency parameters with yield indicate the importance of N nutrition in sunflower; LAI (r=0.841 **), N uptake (r=0.956**), NUpE (r= -0.814**), NUtE (r= -0.787**), NUE (r=-0.802**). Variation in NUE was more closely associated with NUpE (r=0.996**) than NUtE (r=0.812**) and linearly decreased with increasing leaf greenness (R2=0.70) and total leaf area (R2=0.81). This work will complement other studies to establish a baseline for breeding N efficient sunflower genotypes be grown under semi-arid tropical conditions in India and similar environments.