Key technical points for promoting flowering, retaining fruit and improving quality in ponkan
Promoting flowering and retaining fruit and improving quality in ponkan
I. Promoting flowering and retaining fruit
Under conditions of good nutrient accumulation in citrus, proper water control leads to good flower bud differentiation. As a result, ponkan produces many flowers, but also drops many flowers and fruits. Usually a fruiting mature tree has 10,000 to 50,000 flowers, while the fruit-setting rate is only 2% to 8%, and in low-yielding ponkan orchards the fruit-setting rate is less than 1%. Fruit drop in ponkan occurs mainly during the first physiological fruit drop period, with fruits dropping together with their stalks; this is mainly caused by incomplete flower organ development, deformed flowers and poor pollination and fertilization. There is less fruit drop during the second physiological fruit drop period, and its causes are insufficient nutrition, conflict between fruit and shoots, and endogenous hormone imbalance. In addition, weak tree vigor, slender bearing mother branches and bearing branches, rainy and low-temperature weather with little sunshine during the flowering period, weak photosynthesis, abnormally high temperatures and drought during the young fruit stage, as well as wind damage and insect damage, also cause fruit drop in ponkan.
The following measures should be taken to promote flowering and retain fruit:
1. Fertilize and control water to promote flower bud differentiation
Before flower bud formation, in early to mid-November, apply well-rotted organic fertilizer; when flower bud differentiation begins, control water appropriately to increase the cell sap concentration of the tree, which favors flower bud differentiation. For fertilizer, use composted and rotted wheat bran cake (oil cake) or pig and cattle pen manure applied to the soil, or spray the leaves 2 to 3 times with 0.3% potassium dihydrogen phosphate or 1% compound fertilizer.
2. Increase leaves and protect leaves through winter
Ponkan generally has many fruits when it has many leaves, so in cultivation, building strong tree vigor, increasing leaves and preventing leaf drop favor flower bud differentiation and increase yield. Summer and autumn drought can cause abnormal leaf drop, so irrigate or mulch in time. In production areas with freezing damage in winter, protect against cold and preserve leaves; apply organic fertilizer before and after fruit harvest to restore tree vigor, and at the same time carry out pest and disease control well.
3. Regulate flower quantity and improve flower quality
For trees that flower excessively, apply more nitrogen fertilizer before flower bud differentiation to reduce flower quantity and improve flower quality. In addition, rational pruning and thinning out excessively weak and some excessive flower branches can also reduce flower quantity.
4. Apply supplemental fertilizer skillfully to promote flowering and retain fruit
Spring shoot growth and flowering consume large amounts of nutrients, while the carbohydrates produced by new leaves that have not yet turned green are only enough for their own growth; by the time flowers fade, the leaves contain very little nitrogen and phosphorus. Therefore, about 15 days before bud emergence, apply a flowering-promoting fertilizer mainly of nitrogen, and after flowers fade apply phosphorus and potassium fertilizer appropriately, to help reduce fruit drop and allow normal fruit development. However, fertilizer must not be applied too much, to the extent that it does not cause summer shoots to sprout. Fertilization according to the tree is often adopted, that is, trees with few fruits are given little or no fertilizer, while trees with many fruits are fertilized appropriately.
Spraying 0.3% to 0.5% urea during the period when spring shoots turn green can promote spring shoots to turn green; in early to mid-July, apply organic fertilizer heavily to strengthen fruits and promote autumn shoots; from flowering to the young fruit drop period, if there is continuous rain and fertilizer cannot be applied to the root zone in time, foliar fertilization can be used.
5. Control summer shoots and regulate the conflict between shoots and fruits
The sprouting of summer shoots leads to a large amount of fruit drop, so at this time, fertilizer control is used in cultivation to suppress early summer shoots. Besides fertilizing according to the tree after flowers fade, summer shoots that have already sprouted should be removed in time.
6. Use growth regulators and micro-fertilizers for regulation
According to a 1987 experiment by Xu Jiankai and others of South China Agricultural University, in mid-October, when ponkan autumn shoots turn green and mature, spray 500 mg/kg of P333 (paclobutrazol) on all autumn shoots in the middle and upper part of the canopy until dripping; the next year the flower quantity of these autumn shoots was 211% of the control. It should be noted that P333 has an inhibitory effect on citrus growth and must not be used on weak trees. When 3/4 of the flowers have faded, spray 50 mg/kg GA3 plus 0.3% to 0.5% urea or 0.2% potassium dihydrogen phosphate or 0.15% borax, and spray once more after 15 days (0.15% borax may be changed to 0.15% to 0.25% magnesium sulfate); this significantly improves the fruit-setting rate of ponkan.
II. Improving quality
To improve ponkan fruit quality, in addition to selecting and planting superior new varieties and choosing the most suitable ecological zones for planting, measures can be taken in fertilizer, water and fruit thinning.
First, increase the application of organic fertilizer and pay attention to the combination of nitrogen, phosphorus and potassium. Production shows that applying an appropriate amount of phosphate fertilizer can reduce the acid content of the fruit; spraying 0.2% potassium dihydrogen phosphate or 2% calcium superphosphate extract in autumn can significantly increase the sugar content of the fruit and give good coloring. Second, irrigate in autumn and winter, that is, irrigate an appropriate amount before the fruit colors, which can promote fruit expansion and improve quality. Third, thin fruits. After the second physiological fruit drop period ends, a leaf-to-fruit ratio of (40 to 50):1 can enlarge the fruit and improve quality. Fruit thinning also helps promote autumn shoots and reduce off-year fruiting.
Under conditions of good nutrient accumulation in citrus, proper water control leads to good flower bud differentiation. As a result, ponkan produces many flowers, but also drops many flowers and fruits. Usually a fruiting mature tree has 10,000 to 50,000 flowers, while the fruit-setting rate is only 2% to 8%, and in low-yielding ponkan orchards the fruit-setting rate is less than 1%. Fruit drop in ponkan occurs mainly during the first physiological fruit drop period, with fruits dropping together with their stalks; this is mainly caused by incomplete flower organ development, deformed flowers and poor pollination and fertilization. There is less fruit drop during the second physiological fruit drop period, and its causes are insufficient nutrition, conflict between fruit and shoots, and endogenous hormone imbalance. In addition, weak tree vigor, slender bearing mother branches and bearing branches, rainy and low-temperature weather with little sunshine during the flowering period, weak photosynthesis, abnormally high temperatures and drought during the young fruit stage, as well as wind damage and insect damage, also cause fruit drop in ponkan.
The following measures should be taken to promote flowering and retain fruit:
1. Fertilize and control water to promote flower bud differentiation
Before flower bud formation, in early to mid-November, apply well-rotted organic fertilizer; when flower bud differentiation begins, control water appropriately to increase the cell sap concentration of the tree, which favors flower bud differentiation. For fertilizer, use composted and rotted wheat bran cake (oil cake) or pig and cattle pen manure applied to the soil, or spray the leaves 2 to 3 times with 0.3% potassium dihydrogen phosphate or 1% compound fertilizer.
2. Increase leaves and protect leaves through winter
Ponkan generally has many fruits when it has many leaves, so in cultivation, building strong tree vigor, increasing leaves and preventing leaf drop favor flower bud differentiation and increase yield. Summer and autumn drought can cause abnormal leaf drop, so irrigate or mulch in time. In production areas with freezing damage in winter, protect against cold and preserve leaves; apply organic fertilizer before and after fruit harvest to restore tree vigor, and at the same time carry out pest and disease control well.
3. Regulate flower quantity and improve flower quality
For trees that flower excessively, apply more nitrogen fertilizer before flower bud differentiation to reduce flower quantity and improve flower quality. In addition, rational pruning and thinning out excessively weak and some excessive flower branches can also reduce flower quantity.
4. Apply supplemental fertilizer skillfully to promote flowering and retain fruit
Spring shoot growth and flowering consume large amounts of nutrients, while the carbohydrates produced by new leaves that have not yet turned green are only enough for their own growth; by the time flowers fade, the leaves contain very little nitrogen and phosphorus. Therefore, about 15 days before bud emergence, apply a flowering-promoting fertilizer mainly of nitrogen, and after flowers fade apply phosphorus and potassium fertilizer appropriately, to help reduce fruit drop and allow normal fruit development. However, fertilizer must not be applied too much, to the extent that it does not cause summer shoots to sprout. Fertilization according to the tree is often adopted, that is, trees with few fruits are given little or no fertilizer, while trees with many fruits are fertilized appropriately.
Spraying 0.3% to 0.5% urea during the period when spring shoots turn green can promote spring shoots to turn green; in early to mid-July, apply organic fertilizer heavily to strengthen fruits and promote autumn shoots; from flowering to the young fruit drop period, if there is continuous rain and fertilizer cannot be applied to the root zone in time, foliar fertilization can be used.
5. Control summer shoots and regulate the conflict between shoots and fruits
The sprouting of summer shoots leads to a large amount of fruit drop, so at this time, fertilizer control is used in cultivation to suppress early summer shoots. Besides fertilizing according to the tree after flowers fade, summer shoots that have already sprouted should be removed in time.
6. Use growth regulators and micro-fertilizers for regulation
According to a 1987 experiment by Xu Jiankai and others of South China Agricultural University, in mid-October, when ponkan autumn shoots turn green and mature, spray 500 mg/kg of P333 (paclobutrazol) on all autumn shoots in the middle and upper part of the canopy until dripping; the next year the flower quantity of these autumn shoots was 211% of the control. It should be noted that P333 has an inhibitory effect on citrus growth and must not be used on weak trees. When 3/4 of the flowers have faded, spray 50 mg/kg GA3 plus 0.3% to 0.5% urea or 0.2% potassium dihydrogen phosphate or 0.15% borax, and spray once more after 15 days (0.15% borax may be changed to 0.15% to 0.25% magnesium sulfate); this significantly improves the fruit-setting rate of ponkan.
II. Improving quality
To improve ponkan fruit quality, in addition to selecting and planting superior new varieties and choosing the most suitable ecological zones for planting, measures can be taken in fertilizer, water and fruit thinning.
First, increase the application of organic fertilizer and pay attention to the combination of nitrogen, phosphorus and potassium. Production shows that applying an appropriate amount of phosphate fertilizer can reduce the acid content of the fruit; spraying 0.2% potassium dihydrogen phosphate or 2% calcium superphosphate extract in autumn can significantly increase the sugar content of the fruit and give good coloring. Second, irrigate in autumn and winter, that is, irrigate an appropriate amount before the fruit colors, which can promote fruit expansion and improve quality. Third, thin fruits. After the second physiological fruit drop period ends, a leaf-to-fruit ratio of (40 to 50):1 can enlarge the fruit and improve quality. Fruit thinning also helps promote autumn shoots and reduce off-year fruiting.