Factors Affecting Citrus Flower Bud Differentiation and Management During the Flower Bud Stage

Symptoms of Nutrient Deficiencies in Citrus and Their Control: Iron Deficiency

Iron‑deficiency symptoms: 1. Primarily affects young shoots. When iron is deficient, the leaves on new growth turn yellow, while the veins remain green and clearly visible, forming a reticulate pattern. 2. As deficiency worsens, the leaves become yellowish‑white except for the main veins, with margins sometimes turning scorched and drying out, leading to premature leaf drop. Autumn shoots are more severely affected than spring shoots, and yellowing is more pronounced on the outer canopy than in the interior. Correction methods: 1. Increase application of organic fertilizers—such as green manure, pig or cattle pen manure, and composted residues—which are the most effective remedies. For mature citrus trees showing iron‑induced chlorosis, applying 50–100 kg of organic fertilizer per tree annually can help restore normal growth and fruiting. 2. Foliar sprays of 0.2% ferrous citrate or ferrous sulfate can…

Symptoms of Magnesium Deficiency in Citrus and Methods of Prevention and Control

Magnesium deficiency characteristics: 1. It can appear on leaves in any season, but progresses more rapidly in late summer and autumn. 2. Leaves bearing abundant fruit, especially those close to the fruit, exhibit more pronounced magnesium deficiency. 3. Typical symptoms occur on older leaves, with irregular yellow spots along the main veins; these spots gradually expand until only the leaf tip and base remain green, forming an inverted “V” shape at the leaf base. Remedial measures: 1. Apply soil amendments to improve soil conditions. For acidic soils such as red and yellow soils with a pH below 6, apply 0.5–1.0 kg per tree of calcium‑magnesium phosphate, magnesium oxide, or magnesium hydroxide. It is best to compost these materials with organic fertilizers like pig manure or chicken manure, then incorporate the resulting compost into the soil in spring. For alkaline soils such as purple soils…

Symptoms of Calcium Deficiency in Citrus and Methods for Its Prevention and Control

Calcium deficiency symptoms: 1. Weak root growth and a reduced number of new roots. 2. Noticeable leaf drop in the upper canopy and widespread dieback; yellowing at the tips of spring shoots. 3. Increased susceptibility to sunscald, cracking, soft fruit skin, deformed fruits, and sour fruit flavor. Remedial measures: 1. Apply calcium fertilizer to the soil. For acidic soils, apply lime to adjust the soil pH to around 6.5—be sure to make gradual adjustments to avoid harming the root system. This lowers soil acidity and increases the exchangeable calcium content. Application rates depend on soil acidity: for citrus orchards just beginning to show calcium deficiency, apply 35–50 kg of lime per mu; for mature orchards with severe calcium deficiency, apply 1.0–2.5 kg of lime per tree. The method involves first spreading the lime between trees in the orchard or…

Symptoms of Potassium Deficiency in Citrus and Methods for Its Prevention and Control

Potassium deficiency characteristics: 1. Slow growth, few new shoots, small and sparse leaves, and dieback of young branches. Some leaves turn bronze‑colored or exhibit uneven chlorosis. 2. Yellowing of the midribs and lateral veins, with increased susceptibility to sunburn. 2. In severe cases, leaves become twisted and curled, taking on a cupped shape. Fruits show reduced size and thin skin. Correction methods: 1. For soils low in organic matter—such as red soils, red‑yellow soils, light sandy soils, and acidic soils—it is best, when establishing an orchard, to deeply till and incorporate green manure, or to apply additional organic fertilizers, thereby improving soil structure, increasing potassium content and cation exchange capacity, and enhancing overall fertility. 2. For established citrus orchards, adopt a combined approach of chemical and organic fertilization for correction. Organic matter should be thoroughly mixed into the soil, and potassium sulfate should be used as the chemical fertilizer.

Phosphorus Deficiency in Citrus: Symptoms and Control Measures

Phosphorus deficiency characteristics: 1. Spring shoots are few, thin, and sparse; leaves are small, narrow, dark green, with some tips turning brown and dying. 2. Significant impact on fruit: low yield, high incidence of misshapen fruits, and substantial pre-harvest fruit drop. Fruit skin is coarse, thick, and soft; juice content is low, acidity is high, and sugar levels are low. Fruits become soft, exhibit irregular shapes, and develop thicker, rougher skins. Correction methods: Phosphorus is easily fixed by the soil and is not suitable for broadcast application. Therefore, in phosphorus-deficient soils, from March to October, dig planting holes and apply concentrated deep‑burial fertilizers such as superphosphate, calcium‑magnesium phosphate, rock phosphate, and bone meal at a rate of 0.5–1.0 kg per tree. Since phosphorus has poor mobility in the soil and must come into direct contact with roots to be absorbed, when applying phosphate fertilizer, it should be placed directly around the citrus root zone.

Symptoms of Nitrogen Deficiency in Citrus and Methods of Prevention and Control

Nitrogen Deficiency Characteristics: 1. New leaves are small, thin, light green or pale yellow, with uniform coloration. 2. Branches become shorter and thinner, the number of leaves per branch decreases, young shoots die back, and the canopy becomes sparse. 3. Fruit set is low, fruits are small, the peel is smooth, acid content declines, and maturity is slightly advanced. Correction Methods: 1. Strengthen soil management by applying ample well‑rotted organic fertilizer to improve nutrient‑poor soils and increase soil nitrogen levels. 2. Based on the citrus tree’s nutrient requirements at different growth stages and fruit load, apply organic fertilizers or nitrogen‑based chemical fertilizers in a timely, appropriate, and balanced manner. Apply sufficient organic fertilizer or nitrogen‑rich chemical fertilizer 7–10 days before each flush of new shoot emergence and before flowering, as well as during the fruit‑expansion period. Fertilizer application rates depend on root…

Autumn Fertilization for Citrus to Boost Yield

After the beginning of autumn, citrus fruits enter a critical stage of development. To ensure an adequate flower set for the following year and mitigate alternate bearing, in addition to thinning fruit on heavily fruiting trees, it is essential to apply autumn fertilizer in a scientifically sound and well‑timed manner. The importance of autumn fertilization: Starting from the autumn shoot‑growth phase, citrus fruits undergo a second period of rapid enlargement, which demands substantial nutrients, while the emergence of new autumn shoots also requires ample nutrition. During this time, the root system must allocate these nutrients both to support new shoot growth and to fuel fruit expansion. If root vitality is insufficient—particularly as temperatures drop and dry conditions set in after the onset of autumn—the roots can easily decline, impairing their ability to absorb nutrients. This leads to yellowing of the autumn shoots, commonly referred to as “autumn yellowing.”