Deficit irrigation decision-making of indigowoad root based on a model coupling fuzzy theory and grey relational analysis

Abstract

Water scarcity is a critical constraint to the cultivation of medicinal crops. Establishing irrigation requirements for medicinal plants is crucial for the large-scale production of crude drugs in China. To evaluate the response of indigowoad root growth to water deficit (WD) under-mulched drip irrigation, and determine the optimal deficit irrigation mode for this medicinal crop in Hexi Corridor’s desert oasis, two WD levels were applied: mild (65–75% FC [field capacity]) and moderate (55–65% FC). These treatments were implemented during the vegetative growth (VG) and fleshy-root growth (RG) stages, and sufficient water supply maintained during the other plant stages. A total of seven combined treatments were imposed, with sufficient water supply (85–75% FC) as the control treatment. From the 2-year-long (2017, 2018) field experiment’s results, 12 indicators of indigowoad root growth, yield, water consumption and quality attributes were evaluated via weighted fuzzy evaluation and a grey relation-coupling model. Results indicated that, with greater irrigation amounts throughout the plant growth period, the fuzzy evaluation value of growth, yield and water consumption indicators increased whereas their quality indicators decreased. The fuzzy evaluation value of yield indicators of V1G0 (mild WD treatment during VG) was the highest (0.1582, 0.1581), while that of growth indicators was also relatively high (0.1524, 0.1532). Fuzzy evaluation values of growth and yield indicators of V1G1 (mild WD during VG and RG) exceeded those of V1G2 (mild WD during VG and moderate WD during RG), but evaluation value of quality indicators was lower for V1G1 (0.1457, 0.1457) than V1G2 (0.1494, 15155). Based on the weighted grey relation model, the comprehensive score of V1G0 was deemed best. Therefore, to ensure both yield and quality, the V1G1 is recommended. Our results can provide a scientific basis for efficient water-saving cultivation of indigowoad root in Hexi oasis regions.