Effects of biochar application on rice physiological growth and water use efficiency under dry direct-seeded mode

To investigate the effects of various biochar application levels on the growth physiology and water use efficiency of dry direct-seeded rice (DDSR) in the black soil region of north-east China, five biochar application treatments consisting of 2% (BC1), 4% (BC2), 6% (BC3), 8% (BC4) and 10% (BC5) were set, and no biochar application was used as the control treatment (CK). The differences in photosynthetic properties, dry matter accumulation characteristics, water consumption pattern, yield and water use efficiency of DDSR under different biochar application levels were compared and analysed, and the effect of the water use efficiency of leaves (WUE_L) at each growth stage on the water use efficiency of yield (WUEy) was also investigated. The results showed that the photosynthetic properties, dry matter accumulation and water consumption of rice increased and then decreased with increasing biochar application level. Compared with CK, the rice yield increased by 1.6%–52% with biochar application, and the 4% biochar application level showed the most significant increase in rice yield (P < 0.05). The WUEy in the BC2, BC3, BC4, BC1, CK and BC5 treatments gradually decreased in that order. Among the WUEy values, significant increases of 27%, 13% and 8% in the BC2, BC3 and BC4 treatments, respectively, compared with the CK were observed (P < 0.05). The effect of WUE_L at the prophase tiller, late tiller and milk ripening stages on WUEy enhancement was significant.