Key Technical Points for Citrus Cultivation to Increase Sugar and Reduce Acid

Implementing the citrus “increase sugar and reduce acid” technology is an important measure for creating high-grade branded citrus. Through the promotion and application of “increase sugar and reduce acid” technology, citrus quality can be effectively improved, achieving industrial efficiency and increasing farmers' income.

I. Main Technical Measures

1. Promote optimal transformation of citrus orchards. Comprehensively implement tree thinning, large branch thinning and fruit thinning techniques. For densely planted citrus orchards with closed and shaded canopies, adopt tree thinning measures by either completing thinning in one step or gradually reducing the canopy of thinned trees year by year, so that the number of permanent trees per mu is controlled at around 40. Erect and shading large branches on permanent trees should also be removed to form an open-center canopy.

2. Carry out soil improvement in citrus orchards. Rotate and turn the soil in citrus orchards year by year, and around the end of June each year, deeply apply barn manure, livestock manure, citrus straw and other farmyard fertilizers. In spring, spread lime at 100-200 kg/mu on the citrus orchard and then cultivate. In summer and autumn, combine with drought resistance by covering the orchard floor with grass. In winter, apply fertilizer mud, pond mud and other foreign soil to build up the orchard. Adopt various forms of soil improvement to change the conditions of poor soil quality and high acidity of low-hill red soil.

3. Promote scientific fertilization techniques. Currently, citrus fertilization is mostly based on chemical fertilizers, especially in the middle and late stages with emphasis on nitrogen and potassium fertilizers, which increases the acid content of the fruit. It should be advocated to carry out three fertilizations throughout the year: in spring (around the Awakening of Insects), apply nitrogen fertilizer plus organic compound fertilizer or bone meal, fish fertilizer and other fertilizers with high organic matter content; in summer (after citrus fruit set), mainly apply phosphorus and calcium fertilizer plus cake fertilizer. In winter (after fruit picking), apply ternary compound fertilizer. At the same time, pay attention to foliar spraying to promote sugar increase and acid reduction in citrus fruit, while also strengthening tree vigor and improving tree resistance.

4. Strengthen water management in citrus orchards. Drain immediately when waterlogged, and fight drought immediately when dry. Keep the orchard floor moist in spring, drain and irrigate in summer, and irrigate for protection in autumn and winter. If long-term drought occurs one month before citrus harvest, timely irrigation should be carried out for drought resistance; if rainy weather occurs, water should be controlled in time.

5. Promote timely harvesting techniques for fruit. The citrus in our city is mainly Ponkan, and citrus farmers are accustomed to picking early, generally harvesting in early to mid-November. Fruit picked at this time has poor external coloration, and the sugar content inside has not been fully converted, which significantly affects the appearance and internal quality of the fruit. To achieve optimal internal quality, Ponkan fruit should be harvested around November 20, making full use of the large temperature difference between day and night in mid-November to promote natural color change of the fruit appearance and sugar conversion in the internal quality. When picking, select yellow ones and leave green ones, harvesting in batches, which can significantly improve fruit quality.

6. Carry out variety top-grafting and replacement. Introduce Ponkan varieties with fast acid reduction and excellent quality, and carry out top-grafting replacement for inferior varieties.

II. Main Technical Indicators

The technical indicators that should be achieved in the promotion of “increase sugar and reduce acid” technology are:

1. After transformation, the number of trees per mu in the citrus orchard is around 40, the canopy presents a natural open-center shape, with compact structure, full inner canopy, and good ventilation and light penetration.

2. Through deep plowing and soil improvement, increased application of organic fertilizer, spreading lime and other techniques, effectively reduce soil acidity and increase soil organic content to 1.5%-2%.

3. Carry out fruit thinning twice a year in the orchard, stabilize yield at 2500 kg per mu, and achieve a high-quality fruit rate of over 80%.

4. After the promotion of “reduce acid and increase sugar” technology, the external quality of citrus fruit achieves natural coloration with good glossiness, the soluble solids content of the fruit interior reaches over 12%, and the acidity is reduced to within 1%.