Effects of water and fertilizer deficit regulation with drip irrigation at different growth stages on fruit quality improvement of kiwifruit in seasonal arid areas of Southwest China

For a long time, seasonal drought occurs frequently in Southwest China, and the management of water and fertilizer in kiwifruit orchards has no quantitative standards, which seriously affects the yield and quality of kiwifruit. Therefore, the effects of water and fertilizer deficit regulation with drip irrigation (WFDRDI) on the quality of kiwifruit at different growth stages were explored to achieve water and fertilizer saving, and green and efficient production of kiwifruit. We select 'Jin Yan' kiwifruit and set two water deficit levels (W-D20% and W-D40%) and three fertilizer deficit levels (F-D15%, F-D30% and F-D45%) at bud burst to leafing stage (stage I), flowering to fruit set stage (stage II), fruit expansion stage (stage III) and fruit maturation stage (stage IV), respectively, with a full irrigation and fertilization as the control treatment (CK) in 2017 and 2018. Results showed that the WFDRDI at stage II and III had significant effect on fruit physical quality of kiwifruit, specifically, the III-WD40%FD30% and III-WD20%FD45% treatments significantly increased fruit firmness by 13.62 and 15.59% (P<0.05), respectively; the II-WD40%FD15% and III-WD40%FD15% treatments significantly increased dry matter by 8.19 and 6.47% (P<0.05), respectively; the III-WD20%FD15% treatment significantly increased single fruit weight and fruit volume by 9.33 and 12.65% (P<0.05), respectively; the II-WD20%FD15% treatment significantly increased fruit water content by 1.99% (P<0.05). The WFDRDI had an obvious effect on fruit chemical quality of kiwifruit. The III-WD20%FD45%, IV-WD40%FD15% and IV-WD20%FD30% treatments significantly increased vitamin C (Vc) content by 69.96, 36.96 and 34.31% (P<0.05), respectively; the III-WD40%FD15% and IV-WD40%FD15% treatments significantly increased total soluble solid (TSS) content by 3.79 and 17.05% (P<0.05), respectively, and significantly increased soluble sugar content by 28.61 and 34.79% (P<0.05), respectively; the contents of fructose, glucose and sucrose also had a significantly increasing trend, which was increased significantly by 5.58-19.63%, 40.55-60.36% and 54.03-54.92% in the III-WD40%FD15% and IV-WD40%FD15% treatments (P<0.05), respectively; sugar-acid ratio was increased significantly in the IV-WD40%FD15% treatment by 64.65% (P<0.05). The degree and duration of water and fertilizer deficit had a comprehensive effect on fruit quality of kiwifruit. The WFDRDI at stage II and III contribute to improving fruit physical quality, and the threshold of water and fertilizer deficit were 20 and 15%, respectively; stage III and IV are the critical periods for improving fruit chemical quality by water and fertilizer coupling effect, and the threshold of water and fertilizer deficit were 40 and 15%, respectively. Therefore, aiming at precise water and fertilizer saving, the I-WD20%FD30%, II-WD40%FD15%, III-WD40%FD15% and IV-WD40%FD15% treatments under WFDRDI during the whole growth period of kiwifruit were the best mode to improve quality and production of kiwifruit.