Determining optimal deficit irrigation and fertilization to increase mango yield, quality, and WUE in a dry hot environment based on TOPSIS

Rational application of water and fertilizer management practices can not only improve mango (Mangifera indica L.) yield and quality but also improve irrigation water-use efficiency (IWUE). However, few studies have addressed the use of water and fertilizer management practices in hot, dry environments with the aim of achieving relatively favorable levels of these parameters concurrently. We used the technique for order preference by similarity to an ideal solution (TOPSIS) method to identify optimal water and fertilizer management practices that resulted in high fruit yields and high IWUE in Southwest China. A randomized block design study with four irrigation levels [full irrigation throughout the growth period (FI), regulated deficit irrigation during flowering (RDIFS), regulated deficit irrigation during fruit expansion (RDIES), and regulated deficit irrigation at maturity (RDIMS)] and three fertilization levels [FH, a water-soluble compound fertilizer (N:P2O5:K2O = 12:8:40) applied at 129.0 kg ha−1; FM, 103.2 kg ha−1; and FL, 77.4 kg ha−1] was implemented in 2018 and 2019 to investigate these relationships. The net photosynthesis rate (Pn), transpiration rate (Tr) and stomatal conductance (Gs) of mango under the different water deficit treatments were significantly lower than those under the FI treatment with the same fertilization conditions, but the instantaneous water-use efficiency (WUEi) of the leaves increased. The fresh fruit yield, solids:acid ratio (SOAR), sugar:acid ratio (SUAR), and IWUE under the RDIFS treatment were significantly lower than those under the FI treatment at the same fertilization rates. Averaged over all fertilization rates, the fruit yield under RDIES was 8.6–22.3% lower than that under FI in both years, but the IWUE significantly increased from 3.7% to 18.6%. Compared with the FI treatment, the RDIMS treatment had no significant effect on fruit yield but significantly increased the IWUE (35.5–44.7%), total sugar (TS) content (3.7–8.5%), and carotenoid content (CC) (1.5–13.1%) in both years. At the same irrigation level, the Pn, Gs and Tr increased with an increasing fertilization rate, while the fruit yield, IWUE, TS, and vitamin C (VC) content of fresh fruit first decreased but then increased with increasing fertilization rate. IWUE was more closely related to photosynthesis characteristics at the flowering stage than at the mature stage, but fruit quality was more closely related to photosynthesis characteristics at the mature stage than at the flowering stage. Compared with the FIFH treatment, the RDIMSFM treatment significantly increased the fruit yield by 10.1% and 6.6% in 2018 and 2019, respectively, and increased the IWUE by 28.1% and 35.6%, respectively. On the basis of the TOPSIS method, the multi-target optimum scheduling of mango was achieved under the RDIMSFM treatment. The identified optimum combination of water and fertilizer can provide a scientific basis for irrigation and fertilization optimization and management in the hot, dry environment of Southwest China.