Improving the physiological properties and yield of safflower by combining organic and chemical nitrogen in different irrigation cut-off conditions

The purpose of this work was to investigate how different nutrition systems (N0: 0:0, N1: 100:0, N2: 75:25, N3: 50:50, N4: 25:75, and N5: 0:100 kg ha −1 nitrogen from urea and organic fertilizer sources respectively) affect the physiological characteristics and yield of safflower ( Carthamus tinctorius L.) under different irrigation regimes. These irrigation regimes include complete irrigation (S0), irrigation cut-off at stem elongation (S1), flowering and pollination (S2), and grain filling (S3) stages. The S1 irrigation level led to a decrease in Fv/Fm (5 %), relative water content (RWC) of the leaf (17 %), leaf total chlorophyll (22 %), and soluble proteins of the leaf (21 %) an increase in electrolyte leakage (33 %), carotenoids (43 %), proline content (42 %) and soluble sugars of the leaf (39 %) compared with S0 irrigation level. The safflower leaf showed increased Fv/Fm, RWC, total chlorophyll, and soluble proteins when organic fertilizer was used alone or in combination with chemical fertilizers under irrigation cut-off conditions. Additionally, the use of organic fertilizer resulted in a decrease in carotenoid content, proline content, and soluble sugars of the safflower leaf. The highest biological yield was obtained with S0 irrigation level (21.62 t ha −1 ) and N3 integrated nutrition system (21.93 t ha −1 ), respectively. The N3 and N2 nutrition systems increased the grain yield by 3.34 t ha −1 and 3.56 t ha −1 in 2015 and 2016, respectively. The greatest negative effect on biological yield was observed when irrigation was cut-off during the vegetative stage, while the most detrimental impact on grain yield occurred when irrigation was ceased during the flowering and pollination stages. Overall, the results indicated that N2 and N3 nutrition systems while implementing irrigation cut-off at various growth stages reduced the negative impact of water deficiency on plants. This leads to decreased production costs for stress-resistant osmolytes and, consequently, improved grain yield and biological yield. • Drought stress in seed filling stage of safflower decrease grain yield significantly. • Organic and integrated fertilizers improve the soil biological properties. • Application of integrated fertilizer improves the physiological properties of safflower. • Integrated fertilizer moderates the drought stress effects on safflower grain yield.