Multi-objective deficit drip irrigation optimization of citrus yield, fruit quality and water use efficiency using NSGA-II in seasonal arid area of Southwest China

Precision irrigation management is the key to saving water, improving fruit quality and increasing yield of citrus. In this study, six water-yield models and three water-fruit quality models were proposed based on 4-year field data. Then, six scenarios were set with crop total available water (CTW) from 550 to 800 mm at intervals of 50 mm, and a simulation optimization model coupling water-yield, water-fruit quality models and NSGA-II was developed to optimize water allocation strategies. The results showed that six water-yield models performed well in predicting citrus yield, especially Minhas model (R2=0.81). Three water-fruit quality models could well predict the physical quality of citrus fruit (R2=0.72-0.92), but only the Q-Rao model could accurately predict the chemical quality due to its development considering the response processes of fruit quality to deficit irrigation. Therefore, Minhas and Q-Rao models were recommended to predict citrus yield and fruit quality, respectively. The optimization results showed that the optimal water allocation strategy under CTW= 630 mm produced an acceptable yield while improving fruit chemical quality and water use efficiency. When CTW was greater than 630 mm, the optimal water allocation strategy had little difference. Therefore, the optimal water allocation strategy under CTW= 630 mm, which was 14, 104, 325, and 187 mm at bud bust to flowering stage, young fruit stage, fruit expansion stage, and fruit maturation stage, respectively, was recommended to be used under suf-ficient water resources conditions (CTW & GE; 630 mm). When CTW was between 550 and 630 mm, the optimal water allocation strategy changed. As a result, the optimal water allocation strategy was chosen based on the findings as well as the actual local CTW under limited water resource conditions (CTW = 550-630 mm). The findings of this study will be useful in developing appropriate irrigation strategies in Southwest China, to achieve efficient and sustainable citrus production.