Photosynthetic Characteristics and Yield Response of Isatis indigotica to Regulated Deficit Irrigation in a Cold and Arid Environment

Yucai Wang,Chenli Zhou,Hengjia Zhang,Zeyi Wang,Fuqiang Li

doi:10.3390/w13243510

Abstract

Water resource scarcity is an important factor restricting the sustainable development of agriculture in Northwest China. Regulated deficit irrigation can conserve water while maintaining high crop yields. A field experiment was conducted to evaluate the effect of regulated deficit irrigation on the photosynthetic characteristics, yield, and water use efficiency of woad (Isatis indigotica) under mulched drip irrigation from 2017 to 2019 in a cold and arid area of the Hexi Oasis irrigation region, China. Sufficient water was supplied during the seedling stage. The control consisted of adequate water supplied during the other growth stages, whereas mild, moderate, and severe water deficits were imposed during the vegetative growth period, and a mild and moderate water deficit was imposed during the fleshy root growth stage. A mild water deficit was imposed during the fleshy root maturity period. The results showed that the net photosynthetic rate, transpiration rate, and stomatal conductance under moderate and severe water deficit were significantly (p < 0.05) decreased compared with the control, respectively, during the vegetative growth period. The economic yield of mild water deficit during the vegetative growth and mild water deficit during the vegetative growth and fleshy root growth did not differ significantly (p > 0.05) from that of the control. Other treatments caused a 6.74–17.74% reduction in the economic yield of woad. The water use efficiency and irrigation water use efficiency were the highest in the mild water deficit during the vegetative growth period and the fleshy root growth period. Therefore, the application of a continuous mild deficit from the vegetative growth stage to the fleshy root growth stage with sufficient water supplied during other growth periods is recommended as the optimal irrigation regime for maximum yield, water use efficiency, and water-saving of woad.

Highlights

The Hexi Corridor is the main cultivation area of woad (Isatis indigotica) in China due to its unique climatic conditions
The photosynthetic rate (Pn) had increased the most during the vegetative growth period, while that in the fleshy root growth period increased slightly compared with control (CK)
The Pn of CK with sufficient water supply was the highest during the vegetative growth period, but there was no significant difference between CK and WT4, and the Pn of other deficit treatments were significantly lower than that of CK

Summary

Introduction

The Hexi Corridor is the main cultivation area of woad (Isatis indigotica) in China due to its unique climatic conditions. The shortage of water resources restricts the development of woad plantations. Woad (Figure 1) is a traditional Chinese medicinal material, and its leaves (large green leaves) and dried roots (Isatis root) can be used as a medicine, with heat-clearing, detoxification, pharyngeal, pain-relieving, blood-cooling, and anti-inflammatory effects. Woad root can be processed into granules (Isatis root granules). The product is very popular in China and is most often dissolved in hot water or tea [1]. It is the most commonly used heat-clearing and detoxification medicine in

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