Effects of Water and Nitrogen Coupling on Photosynthetic Characteristics, Yield and Quality of Isatis Indigotica
Abstract In arid areas of Northwest China, Isatis indigotica is a commercial medicinal crop cultivated with higher water and nutrient in a large area, which makes rational irrigation and nitrogen application key factors for successful crop management. The objective of this study was to determine the effect of water and nitrogen coupling on photosynthetic characteristics, yield, and quality of Isatis indigotica produced in northwestern China. Field trials were conducted for two consecutive years on the irrigation test station. Data on photosynthetic parameters, yield and quality were collected from individual Isatis indigotica for each treatment during the years 2018–2019. The application of nitrogen significantly increased photosynthetic rates and yield under the same irrigation conditions. However, the yield were reduced in the excess water treatments, W3N1, and W3N2 and in excess nitrogen treatments, W1N3, W2N3, W3N3, in contrast to the optimum W2N2 treatment. Moreover, the quality indicators of the W2N2 treatment decreased compared with CK, which was due to water stress and more photo-assimilates being available to the roots, but the effective quality index value cloud be effectively improved by greatly increasing the yield.