Effect of biochar addition and reduced irrigation regimes on growth, physiology and water use efficiency of cotton plants under salt stress

To alleviate the salinity and drought stresses faced in agricultural production, and to improve crop water use efficiency (WUE) in drought-prone regions, novel management strategies are needed. The combination of bio-char amendment and reduced irrigation regimes could mitigate the negative effects of salinity and drought stresses and improve WUE of cotton plants. A split-root pot trial was performed in order to investigate the effects of two biochar amendments [wheat straw pellets biochar (WSP) and soft wood pellets biochar (SWP)] combined with three irrigation schemes [full irrigation (FI), deficit irrigation (DI), and partial root-zone drying irrigation (PRD)] on the growth, physiology and WUE of cotton plants under two salinity levels [0 mM NaCl (S0) and 200 mM NaCl (S1)]. The results showed that salt stress depressed plant growth and physiology, and reduced seed cotton yield and lint yield by 19.33-47.22% and 40.43-58.81%, respectively. However, the biochar amendment alleviated salt stress and increased plant dry biomass allocation ratio by 3.85%-12.54%, 5.07%-14.39% and 9.78%-46.62% in boll, seed cotton and lint cotton under S1, respectively, and also increased lint ginning out turn (GOT), harvest index (HI), WUE at plant and yield level (WUEp and WUEy) by 0.21%-28.69%, 5.07%-14.39%, -0.30%-15.71% and 5.83%-32.44%, respectively. Moreover, WSP was superior to SWP in terms of improving plant growth and yield. PRD showed better growth and physiological effects than DI, especially WUEp and WUEy were 6.88%-13.73% and 9.16%-22.78% greater under PRD than under DI. The combined application of biochar and PRD counteracted the decrease in WUE caused by biochar application alone under S0. Collectively, WSP combined with PRD could be a promising strategy in sustainable cotton production under drought and salinity stress.