High-Yield Facility Cultivation Techniques for Moving Pomelo (Citrus maxima) from the South to the North

I. Field Establishment and Orchard Construction The cultivation technique for moving pomelo from the south to the north is carried out by combining open-field management with plastic-film-covered greenhouse management. The entire growth period is divided into open-field cultivation management and protected cultivation management, that is, from early October each year to early May of the following year, local conventional winter-warm greenhouse cultivation management is used, which belongs to protected cultivation management; at other times, the film can be removed and the plants grow in the open field, which belongs to open-field cultivation management. The planting time is February to March each year. At planting, the spacing between plants and rows is 3×2 m, with 111 plants per mu; ditching or digging planting holes is adopted, with deep plowing to 60 cm; then high-quality farmyard manure or pen manure is applied, generally 5000 kg per mu, mixed with 100 kg of compound fertilizer. After planting, water thoroughly and cover with plastic film.

II. Fertilizer and Water Management In the year of planting, the comprehensive management of soil, fertilizer and water in the greenhouse should be strengthened. Pomelo can be top-dressed 1 month after planting and surviving, and then top-dressed again every 1.5-2 months, with 0.1-0.3 kg of urea or compound fertilizer per plant each time. Mature pomelo trees should be fertilized 3-5 times per year, that is, one basal fertilizer application and multiple top-dressings. Basal fertilizer is generally applied after fruit harvest, with 30-50 kg of high-quality organic fertilizer per plant, plus 0.5-1 kg of calcium magnesium phosphate. This application should account for 60% of the total annual fertilizer amount. Fruit-preserving fertilizer is applied in June-July, accounting for 10% of the annual total, with increased use of phosphorus and potassium fertilizers. Flower-promoting fertilizer is applied in September-October, accounting for 20% of the annual total, with a combination of nitrogen, phosphorus and potassium. Fruit-strengthening fertilizer is applied from December to January of the following year, accounting for 10% of the annual total, mainly potassium fertilizer. In addition to normal soil fertilization, attention should also be paid to multiple foliar top-dressings. Special attention should be paid to spraying a 400-fold borax solution at the flowering stage to promote pollination and fertilization and improve fruit set. Spraying 0.3% urea plus 0.2% monopotassium phosphate at the young fruit stage can reduce fruit drop and promote fruit enlargement. Spraying a 0.2% monopotassium phosphate solution at the flower bud differentiation stage can promote nutrient transformation and make flower buds plump and full. Watering should be carried out together with fertilization. Pomelo likes a humid environment, and the relative soil water content should be maintained at 60%-80%; when irrigating, apply small amounts but frequently.

III. Training and Pruning The main methods are natural open-center or “V” shaping. The trunk height is generally about 50 cm, the number of main branches is 2-3, and side branches are left on both sides of the main branches in staggered distribution, in a horizontal or curved state. During pruning, different methods such as heading back, leaving unpruned, thinning out and renewal pruning are mainly adopted, so that new shoots can achieve the purpose of bearing fruit. In addition, after fruit harvest, the fruiting branches should be renewed. This can promote earlier flowering of the plant and lay the foundation for a high yield the following year.

IV. Regulation of Temperature and Humidity From early October each year to early May of the following year is the growth period under artificially controlled greenhouse conditions, and at other times the plants can grow completely under open-field conditions. Therefore, whether the temperature and humidity regulation under facility cultivation conditions is reasonable and appropriate is crucial. The temperature and humidity regulation for facility cultivation of pomelo moved from the south to the north is: during the fruit enlargement stage, daytime temperature 28-32℃, nighttime 10-15℃, relative humidity 60%-80%; during the near-ripening stage, daytime 26-30℃, nighttime 8-13℃, relative humidity 60%-80%; during the young shoot growth stage, daytime 17-22℃, nighttime >5℃, relative humidity <80%; during the flowering stage (April), daytime 22-25℃, nighttime >12℃, relative humidity about 60%.

V. Disease and Pest Control Adhere to the principle of “prevention first, integrated control” on the basis of strengthening comprehensive management and improving the disease resistance of the tree, rationally spray biological agents and high-efficiency, low-residue pesticides. In cultivation observations, the main diseases and pests of pomelo are, first, powdery mildew, and second, leafminer. For powdery mildew, spray 5 degrees Baume lime sulfur mixture before bud break; during the growing season, use 20% triadimefon emulsifiable concentrate at 3000-fold dilution or 30% triflumizole at 2000-fold dilution. For leafminer, spray 1.8% avermectin emulsifiable concentrate at 3000-fold dilution during the occurrence period.

VI. Picking and Harvesting Pomelo is marketed successively from late December to February of the following year, with a picking period as long as 2 months, and its main ripening period is controlled around the Spring Festival. Because of picking in stages and marketing while picking, a high yield of 1000 kg per mu for one-year-old trees, 2200 kg per mu for two-year-old trees, and 4100 kg per mu for three-year-old trees can be achieved.