Foliar Application of Biostimulants to Improve Growth, Yield and Fruit Quality of ʻValenciaʼ Orange Trees Under Deficit Irrigation Conditions

Abstract

Water is one of the most important components that affect plant growth and productivity. Foliar application of some biostimulants may reduce the amount of used water. New agricultural practices intended to enhance water use efficiency, require careful study to determine their effects on optimal irrigation levels. To examine the effect of irrigation and biostimulants spray on tree growth, yield and fruit quality, this research was carried out on seventy-two ‘Valencia’ orange ( Citrus sinensis, Osbeck) trees grown at 5×5 m spacing in a private orchard at Badr district, Behaira Governorate, Egypt during 2017/2018 and 2018/2019 seasons. Trees were budded on ‘Volkamer’ lemon rootstock and grown in sandy soil under drip irrigation system. Three drip irrigation regimes were applied at 25,866; 19,240; and 12,933 L/tree/year, which represent about 100, 75, and 50% of tree water requirement using 16, 12, and 8 drippers/tree, respectively. Each irrigation regime was combined with the foliar application of tap water (control), seaweed extract (2.5g/L), fishmeal extract (10g/L) or compost tea extract (65ml/L). Foliar treatments were applied three times; three weeks before flowering, at full bloom and two months after full bloom. Results indicated that as irrigation volume increased, there was significant improvement in the vegetative growth, fruit set percentage, but the percentage of June fruit drop and preharvest fruit drop was negatively related to water volume. The greatest incremental effect between treatments generally occurred with the intermediate level of irrigation, which actually had significantly higher yield and fruit quality than the full irrigation treatment in both years. Foliar application of seaweed, fishmeal, or compost tea extracts enhanced tree growth, fruit set, total yield, and fruit physical and chemical characteristics. Compost tea had the most pronounced effect in this regard. Overall, the best results were obtained with the combination of 19,240 tree/year plus compost tea (65ml/L) for tree vegetative growth, fruit set, less fruit drop, total yield and most of fruit quality aspects. Furthermore, this combination saved about 25% of the total used water, and increased total yield per tree by 40.7% over the control.