Effects of water, salt and nitrogen stress on sunflower (Helianthus annuus L.) at different growth stages

Experiments in soil columns were conducted to evaluate the single and interactive effects of water, salt and nitrogen stress at different sunflower (Helianthus annuus L.) growth stages in Hetao Irrigation District, China. The study factors included soil salinity (S-0 : ECe = 2.5-3.6 dS m(-1); S-1 : ECe = 9.6-10.7 dS m(-1)), soil moisture (W-0 : 35 %-55% of field water capacity; W-1 : 75%-100% of field water capacity), and nitrogen application rates (N-0 : 0 kg N ha(-1); N-1 : 135 kg N ha(-1)). The results indicated that the S-1 treatments increased the duration of the seedling stages by 23.91% but decreased the duration of maturity by 33.09% on average compared with the S-0 treatments. Similarly, water deficit significantly retarded anthesis and prolonged the total growth period. The comprehensive stress assessment index (CSAI) was obtained using principal component analysis (PCA) and membership function analysis (MFA). The CSAIs in different treatments showed that soil salinity was the main limiting factor for sunflower vegetative growth from seeding to bud (SS1), whereas water stress dominated the development from bud to flowering (SS2) and flowering to maturity (SS3). Although statistically non-significant, nitrogen stress was intensified after bud initiation and the CSAI in W1S0N0 treatment was 40.68% lower than W1S1N1 treatment in SS3. Moreover, the interactive effects of the three factors were complicated. Our experiments suggested that adequate water supply after bud initiation and the reasonable nitrogen application rate (135 kg N ha(-1)) can alleviate adverse effects on sunflower reproductive growth under different saline conditions.