Effects of Regulated Deficit Irrigation On Yield and Quality of Isatis Indigotica in a Cold and Arid Environment
Abstract Field experiments were conducted to study the effects of regulated deficit irrigation on net photosynthetic rate, yield, water use and quality of Isatis indigotica under mulched drip irrigation in Hexi oasis region, which can theoretically guide researches on efficient water saving of Isatis indigotica planting. In 2016 and 2017, the experiments of regulated deficit irrigation of Isatis indigotica were carried out at Yimin Irrigation Experimental Station, Minle County, of Gansu Province, China. Except for sufficient irrigation at seedling and maturity of fleshy roots, Isatis indigotica in vegetative stage and fleshy root growth stage were subjected to mild, moderate and severe water deficit respectively, and their photosynthetic physiological indexes, yield and water use were measured. The results showed that the moderate and severe water deficits in vegetative and fleshy root growth stage significantly decreased the net photosynthetic rate and the amounts of dry matter accumulation of Isatis indigotica leaves (P<0.05), and with the increase of water deficit degree, the decrease of the net photosynthetic rate was greater; while the difference between mild water deficit and control group was not significant (P>0.05). The yield and water use efficiency of Isatis indigotica subjected to mild water deficit in vegetative and fleshy root growth stage marked the highest, reaching 8,239.56 kg/hm2 and 8,390.80 kg/hm2, 24.11 kg/hm2 and 23.62 kg/hm2·mm, respectively; other water deficit treatments were reduced, which was significantly different from the control group (P<0.05). Mild and moderate water deficit could increase the content of effective components ((R, S) - Goitrin, indirubin and indigo), and improve the quality of Isatis indigotica, but severe water deficit was not conducive to the accumulation of effective components. Therefore, the optimal water regulation treatment of Isatis indigotica is the mild water regulation deficit in vegetative and fleshy root growth stage, which can reduce the water consumption of Isatis indigotica and effectively improve the quality and its water use efficiency without reducing its yield.