Biochar Application Affected Biochemical Properties, Yield and Nutrient Content of Safflower under Water Stress

Biochar application to soil is a new strategy for managing crop residues, improving soil fertility and increasing soil capacity for water holding. To investigate the effects of wheat (WB) and cotton biochar (CB) application alone or combined with nitrogen (N) and phosphorus (P) chemical fertilizers on biochemical properties, dry matter remobilization, yield and yield components of safflower under normal irrigation and water stress (irrigation cut-off at flowering stage), a two-year field experiment was laid out in 2019 and 2020.  In both years, the total water applied in chemical treatments (150N+50P and 112.5N+37.5P) under water stress, was higher than the other treatments, significantly. During two years, the application of 112.5 kg N + 37.5 kg P+ 3 ton ha^-1 of cotton biochar (112.5N+ 37.5P+ 3CB) increased the relative water content (RWC) from 57.5 to 59.4% and the total chlorophyll content from 80.7 to 128.1%, compared to control under water stress. The carotenoid content and catalase and peroxidase activity in 112.5N+ 37.5P+ 3CB were less than chemical fertilizers due to the role of biochar in water holding. Under water stress, the seed yield of 112.5N+37.5P+3CB was 10.2 and 12.6% higher than 112.5N+37.5P+3WB in 2019 and 2020, respectively. CB had higher macro and micronutrient content compared to wheat biochar and when CB was combined with chemical fertilizers, the nutrient availability and seed yield improved, synergistically. Overall, in fertilizer treatments, all traits except the catalase, peroxidase and carotenoid content were higher under normal irrigation compared to water stress. In 112.5N+37.5P+3CB, the high chlorophyll content, RWC, remobilization efficiency and nutrient content were related to seed enhancement. Results suggest that CB combined with a 75% recommended dose of N and P, might be the best operation for safflower production under water stress conditions.