Fruit yield and quality response of Newhall navel orange to different irrigation regimes and ground cover in Chongqing Three Gorges Reservoir area

In order to reduce unwanted negative effect of frequent rainfall in spring and high-temperature in summer on fruit yield and quality of Newhall navel orange trees in Chongqing Three-Gorges Reservoir area. In this study, the influence of Tyvek® nonwoven materials ground cover (TC) and with different irrigation density 110% (ID110), 60% (ID60), and 0 (ID0) of the local evapotranspiration (ETc) on yield and fruit quality were evaluated during three consecutive years (2015-2017) in a commercial Newhall navel orange drip irrigated orchard. During spring frequent rainfall period, all TC treatments had a significant higher in leaf sucrose content and leaf starch content during flower bloom period due to their significantly increased the leaf ACO2 exchange parameter compared to CK group. As a result, the highest in the number of fruit bearing (FBN) was obtained in TC+ID60 group due to its 84.6% and 13.5% higher the total flower number (TFN) than CK and TC+ID110 groups, respectively. However, the TC+ID110 and TC+ID0 groups had a significantly lower FBN due to their significantly 38.3% and 19.9% rate of dropped flowers (FLDR) compared to TC+ID60 group. During summer high-temperature period, the leaf water potential significantly decreased in order: TC+ID110, TC+ID60 and CK, TC+ID0, which resulted in the significant higher ACO2 and transpiration rate in TC+ID110 and TC+ID60 groups, and significant lower ACO2 and transpiration rate in TC+ID0 group. Consequently, there was a significant increase of total soluble solids, titratable acid, vitamin C in fruit internal quality and “a”, “b”, “a/b” value in fruit external quality, and a significant decrease of juice yield in fruit internal quality and fruit shape index, and weight per fruit with increasing water stress as compared to TC+ID110 group. In conclusion, TC+ID60 treatment can reduce the negative effect of frequent rainfall spring and high summer temperatures and improve the fruit yield and quality of Newhall navel oranges.