Detailed explanation of plastic greenhouse cultivation techniques for large-fruited sweet carambola
Large-fruited sweet carambola is a tropical and subtropical evergreen fruit tree that grows fast, bears fruit early, flowers and fruits multiple times a year, and produces excellent fruit that is crisp and juicy, making it deeply loved by people. However, for a long time, carambola cultivation has been managed extensively, with low per-unit yield, poor quality, and relatively weak market competitiveness and economic benefits. Therefore, in April 2001, our institute began cultivating large-fruited sweet carambola in plastic greenhouses, with an area of 0.43 hm2. Fruit was set in the same year of planting. The yield per hectare was 5700 kg in the first year, 27000 kg in the second year, and 63000 kg in the third year, maturing 30-40 d earlier or 50-60 d later than open-field cultivation, with an annual fruiting period of 8-10 months. At the same time, it improved quality, avoided wind and rain disasters during the ripening period and low-temperature frost damage in winter, and greatly improved market competitiveness and economic benefits.
1 Building a plastic greenhouse orchard
1.1 Orchard establishment: Choose level land with deep soil, loose soil texture, and convenient drainage to establish the orchard. The orchard is built with a multi-span greenhouse supported by steel pipe frames. Each greenhouse is 6 m wide, and the height and length depend on the terrain. Insect-proof netting is installed around the greenhouse, and a shade net plus polyethylene anti-drip film covers the top. Drainage ditches are opened around the perimeter. Appropriate close planting is adopted, with a plant-row spacing of 2.5 m x 3.5 m. Dig large holes 0.8 m long and wide and 1 m deep. Apply 50 kg of farmyard manure, 30 kg of poultry and livestock manure, 1 kg of superphosphate, and 0.5 kg of lime powder per hole, mix thoroughly with the hole soil as base fertilizer, and backfill the hole to 10 cm above the ground.
1.2 Variety selection: Choose high-quality varieties such as Malaysian red carambola and Taiwan large-fruited sweet carambola.
1.3 Planting: Plant from March to May in spring. When planting, compact the soil around the roots, form a mound, trim the tree basin, water thoroughly to settle the roots, and cover the tree basin with grass.
2 Soil and water management
Large-fruited sweet carambola prefers high temperature and humidity, but its root system is not tolerant of waterlogging, and the root mass is relatively shallow and easily affected by drought. Therefore, drainage ditches must be cleared around the orchard to lower the groundwater level. Before the rainy season arrives, carry out one full-orchard tillage and loosening of the soil, preferably to 6-8 cm without injuring too many roots, to improve soil drainage and aeration and prevent compaction after rain. In long droughts without rain, irrigate in time to keep the soil consistently moist. Before the autumn drought, from September to October, carry out another full-orchard tillage and loosening of the soil to reduce water evaporation from the orchard and increase soil temperature. During the frost period, irrigate more to prevent freezing damage and drought-induced leaf drop and maintain tree vigor.
3 Nutrition and fertilization: After young large-fruited sweet carambola trees are planted and survive, apply diluted decomposed human and livestock manure urine water or fermented bran water 1-2 times per month, and the concentration and amount can be appropriately increased each time. Stop application after November, and instead spray 0.2% potassium dihydrogen phosphate 2-3 times. At the end of December, apply decomposed poultry and livestock manure mixed with superphosphate, 5-10 kg per plant.
From the second year onward, fertilize according to the shoot flush, flowering, small-fruit turning stage, and fruit development period of large-fruited sweet carambola [1], generally 4-5 times per year. 1 Shoot-strengthening and flower-promoting fertilizer: Apply in April to May, preferably quick-acting nitrogen fertilizer, with 2.5 kg of peanut bran and 0.5 kg of urea per plant; 2 Fruit-strengthening and fruit-retention fertilizer: Apply in June to July when the main crop fruit is as large as a thumb and begins to turn and hang down. Use superphosphate, peanut bran, and human manure urine in a ratio of 1:2:100, fermented and applied, 25 kg per plant; 3 Flower-strengthening and fruit-strengthening fertilizer: Around August, when the fruit has set its shape and is growing rapidly while flowering continues, apply according to the amount and type of fertilizer used for fruit retention, and pay attention to combining it with irrigation; 4 Fruit-ripening fertilizer: Apply when the fruit has set its shape, mainly urea, 50 g per plant, which can promote early ripening of the fruit and improve quality. At this time, water should be appropriately controlled; 5 Overwintering and cold-prevention fertilizer: After December, apply heavy fertilizer, mainly organic fertilizer, with 30-50 kg of poultry and livestock manure per plant, and cover with soil after application.
4 Pruning and training
After the seedlings are planted and survive, cut the top high at 40-50 cm above the ground to set the trunk, prompting buds on the main trunk to sprout, and select and retain 3-5 strong buds to train as main branches to form the crown framework. When the first-layer branches arising from the main branches each reach 50 cm, remove the terminal buds to promote the sprouting of second-layer branches. Keep 2-3 lateral buds on the second-layer branches and remove all the rest. After that, allow natural branching and appropriately guide the growth direction so that branches at all levels are evenly distributed [2]. Bearing trees are generally pruned once from after fruit harvest in autumn and winter to before spring buds break, mainly to remove dead branches and fallen leaves on the tree and promote the sprouting of spring shoots. Large-fruited sweet carambola trees generally grow vigorously at the top and have many water sprouts, so from late May to early June, timely heading back or thinning should be carried out to suppress growth at the upper part of the crown and promote more fruiting in the middle and lower parts. When pruning, attention should be paid to retaining the drooping, mature "horsewhip branches" around the crown, because these are the best fruiting branches of large-fruited sweet carambola. In addition, when cutting off shade-grown branches inside the crown, leave 1-2 cm branch stubs so that more flower branches or leafy fruiting branches can emerge and more fruit can set at the branch tips.
5 Flower and fruit retention
5.1 Configure pollinizer trees: Mixed planting of Malaysian red carambola and Taiwan large-fruited sweet carambola can increase the fruit-setting rate.
5.2 Prevent drought, typhoons, and frost damage If the flowering period encounters dry, high-temperature, and strong-sunny weather, spray water to protect the flowers. In typhoon and rainstorm seasons, support the tree crown around its perimeter with bamboo or wooden poles and tie and secure the branches to reduce fruit drop caused by typhoons and storms. Before frost arrives, cover with film for protection, irrigate in time, and increase the application of organic fertilizer.
5.3 Hormone-assisted fruit retention: Spraying a 50 mg/L GA3 solution on the leaves at full bloom and the small-fruit stage has an obvious fruit-retention effect.
5.4 Girdling or wire girdling to promote flowering and retain fruit: For young trees with excessive vegetative growth, in mid-to-late June, girdle the bark of the main trunk in 1 ring at 10-15 cm above the ground, with a depth just past the phloem without injuring the xylem, or use No. 10 iron wire to girdle 2 rings, until mid-August when the wire has not completely sunk into the bark, then loosen it [2].
6 Fruit thinning and bagging
Fruit thinning is carried out twice. The first time is within 20-30 d after fruit set, when the fruit turns and hangs down, remove diseased and insect-damaged fruit, deformed fruit, and overly dense small fruit growing in clusters; the second time is when the fruit reaches 4-5 cm in transverse diameter, and before bagging, remove diseased and insect-damaged fruit, deformed fruit, and small fruit in the same batch that cannot keep up with the growth rate. In addition, to improve fruit quality, obtain a good fruit appearance, and increase commercial value, single-fruit bagging is recommended. The method is, after the final fruit thinning and after spraying once comprehensively with fungicides such as 50% thiophanate-methyl or carbendazim, bag individual fruits with waxed paper bags the next morning after the dew has dried, and mark the bagging date so as to distinguish the times of successive batches and facilitate harvesting.
7 Pest and disease control
Because plastic greenhouses plus insect-proof netting are used for cultivation, large-fruited sweet carambola has fewer insect pests, but attention should still be paid to preventing pests such as bird-feather moths, aphids, black-spotted brown tortrix moths, and fruit flies. Focus on applying pesticides during two periods: first, spray 800-fold 90% trichlorfon solution before flowering; second, after the fruit turns, use black light traps to kill black-spotted brown tortrix moths, and during peak outbreak periods spray 800-fold 90% trichlorfon solution plus 4000-fold deltamethrin solution. The main diseases include branch blight, bald-top disease, leaf spot, and anthracnose, so cultivation management should be strengthened to improve the disease resistance of the tree. For diseased plants, pesticides such as Bordeaux mixture or copper hydroxide can be sprayed for control.
8 Regulation of temperature, humidity, gases, and light
Large-fruited sweet carambola likes a high-temperature and high-humidity climate and is relatively shade-tolerant. It avoids strong sunlight and the cold northwest wind, and especially during flowering and the young-fruit stage it is most afraid of dry wind and strong sunlight. It grows poorly below 10°C, and when approaching 0°C the branches and leaves are damaged, and young trees are easily frozen to death. Entering the flowering stage, temperatures above 27°C are needed for good pollination and fruit set. Therefore, properly regulating temperature, humidity, light, and ventilation is the key to successfully cultivating large-fruited sweet carambola in greenhouses.
8.1 Temperature regulation: Regulate greenhouse temperature according to meteorological data. The main methods of raising temperature are covering and irrigation, and water spraying [3]. When the winter temperature drops to 10°C, cover the greenhouse top with polyethylene anti-drip film, and also surround the perimeter with film, keep the greenhouse door tightly closed day and night, and raise the temperature inside the greenhouse and the soil temperature. If hot sunny weather occurs and the temperature inside the greenhouse reaches above 30°C, open the greenhouse door for ventilation and temperature control, irrigate, and spray water. When summer temperatures rise above 30°C, promptly remove the surrounding film, top film, and greenhouse top, and add a shade net. Cover with film; cooling methods are removing the film and ventilation.
8.2 Humidity regulation: During the new shoot growth period, keep the relative humidity inside the greenhouse at 70%; from flowering to the fruit enlargement stage, 50%-60%; during the coloring stage, 50%. If humidity is insufficient, irrigate and spray water; if humidity is too high, carry out ventilation, aeration, and tillage.
8.3 Gas regulation: When cultivating large-fruited sweet carambola in greenhouses, because the air does not flow or flows little, respiration produces CO2 and photosynthesis consumes CO2, so the CO2 concentration inside the greenhouse changes considerably. The leaf photosynthetic rate of large-fruited sweet carambola often decreases at midday, forming a "midday depression phenomenon," which is caused by the relatively low CO2 concentration inside the greenhouse. The main ways to increase CO2 content inside the greenhouse are: first, applying organic fertilizer, which continuously produces CO2 gas during decomposition; second, ventilation and air exchange, so that CO2 in the atmosphere is supplemented into the greenhouse; third, applying CO2 gas fertilizer. In addition, because the air inside the greenhouse circulates little, harmful gases such as NH3, NO2, SO2, and CO are easily produced, so in cultivation too much nitrogen fertilizer should not be applied at one time, and after application water should be given. When the concentration of harmful gases is relatively high, ventilation and air exchange should be carried out.
8.4 Light regulation: When cultivating large-fruited sweet carambola in greenhouses, insufficient light is generally likely to occur, so measures to increase light should be adopted. The methods are to correctly choose the orientation of the greenhouse and design it scientifically so that the interior receives stronger light for a longer time as much as possible. At the same time, choose anti-drip film with good light transmittance and replace old film every year. Laying white plastic film on the ground can increase reflected light.