Proper deficit irrigation applied at various stages of growth can maintain yield and improve the comprehensive fruit quality and economic return of table grapes grown in greenhouses*

In order to investigate the quantitative response of yield, fruit quality and economic return of table grapes grown in greenhouses under deficit irrigation applied at various growth stages, experiments were conducted in 2017 and 2018. Three irrigation levels (full irrigation, 2/3 and 1/3-full irrigation) were applied at the fruit setting-swelling (stage 2), veraison (stage 4) and whole growth stages. The comprehensive fruit quality index (Q(c)) was determined in order to evaluate the overall quality of the berries and its effect on economic return. The results showed that deficit irrigation significantly decreased evapotranspiration (ET) and yield, and improved water use efficiency (WUE), individual quality parameters and Q(c). Fruit quality was more sensitive to water deficit at stage 4 than at stage 2. Significant linear functions were found between a relative decrease in yield, berry quality parameters, Q(c) and a relative seasonal ET deficit. Net income under deficit irrigation was related to the price proportional coefficient (R). Higher net income was mainly determined by a higher yield when R was less than 1, while higher net income was determined by a higher Q(c) when R was greater than 3. An appropriate water deficit level at stages 2 and 4 (F2/3V2/3) is recommended as an optimal treatment as it produces a higher Q(c), the highest WUE and net income without a significant decrease in yield.

Automated summary

Deficit irrigation significantly affects grape yield and fruit quality, with fruit quality being more sensitive during the veraison stage. Linear relationships were found between relative seasonal ET deficit and a decrease in yield, berry quality parameters, and overall fruit quality index. Deficit irrigation can improve water use efficiency and net income, with optimal treatment recommended at certain growth stages for higher quality, efficiency, and income.