Studies on water management to produce high -quality fruit of satsuma mandarin 'Obarabeniwase': II water management techniques under sheet mulching culture and investigation of water stress index
2019
Yamada, H. | Iga, H. | Kawaji, M. | Abe, M.
The optimal level of water stress in Satsuma mandarin 'Obarabeniwase' under sheet mulching culture was investigated with the aim of establishing water management techniques to produce high-quality fruit. Next, the relationship of integral water stress and Brix increase or fruit enlargement was performed regression analysis. Then, the possibility of a water stress index that can be used in the field was investigated. 1. Applying water stress of about -0.7 MPa in terms of leaf water potential (ψmax) from late July to early September to increase in Brix and then easing water stress to about -0.5 MPa from mid- or late September to encourage fruit enlargement and reduce acid concentration resulted in the production of fruit with Brix value of 12.0 degrees and citric acid concentration of about 1.00%. 2. As guidelines when implemented this water management, time-based reference values for Brix increase, fruit enlargement and daily fruit enlargement were calculated. As a result, it was indicated that the following values can be used as yardsticks to maintain water stress at about -0.7 MPa (ψmax) in the 50-day restricted irrigation period from July 20 to September 10: increase in Brix value of 2.9 degrees, enlargement of fruit diameters of 15.2 mm, and daily enlargement of fruit diameters of 0.26 to 0.29 mm from late July to end of August or 0.34 mm in early September. 3. Integral water stress until late September, when next irrigation period is terminated was estimated with Brix increase and fruit enlargement from July 20. It was determined that this predicted value of integral water stress can be used to estimate ψmax for 10-day periods within the restricted irrigation period (late July to early September, until water stress is eased).
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