Summary of Experimental Trials on Delayed Cultivation Techniques for Hongxue Peach in Plastic Greenhouses

Hongxue peach is an extremely late-maturing peach variety. When cultivated in the open field in our county, the fruit is difficult to ripen due to late-autumn rainfall and frost. Therefore, starting in 2001, we conducted delayed cultivation trials in plastic greenhouses using technical measures such as early promotion followed by later control, delayed flowering, bagging to protect against rain, and covering the greenhouse to regulate temperature, prevent frost, and protect leaves. The results showed that facility-grown Hongxue peach bore fruit in the second year after planting, entered full production in the third year, could delay fruit ripening by about 20 days, and markedly improved fruit maturity and the rate of high-quality fruit.

1 Basic Information on the Trial Greenhouses

The trial greenhouses were located in Sangchuan Village, Lianhua Town. The local altitude is 1456 m, the average annual temperature is 9.8°C, the average annual rainfall is about 380 mm, the sunshine duration is 2138 h, and the frost-free period is 166 days. The soil is loessal soil with a deep soil layer, an organic matter content of 0.89%, and a pH value of 8.1, irrigated with well water. The trial trees were planted in 2 plastic greenhouses. The plastic greenhouses have a circular-arched plastic-steel frame structure, run east-west, are 50 m long, 7.0 m wide, 3.8 m high at the ridge, and 1.5 m high at the shoulder. A 60 cm-wide roll-up film ventilation strip is installed at the shoulder, and each end of the greenhouse has one working door. The arched frame is covered with drip-free film.

2 Delayed Cultivation Technical Measures

2.1 Planting was carried out using high-yield pits. In early March, pits of 60×60 cm were dug in the greenhouse, and 20 kg of organic fertilizer and 0.5 kg of special fertilizer for fruit trees were applied, mixed with topsoil, backfilled, compacted, watered, and then covered with soil. After the high-yield pits were dug, the greenhouse was covered to raise soil temperature. In mid-March, finished Hongxue peach seedlings were planted at a spacing of 1 m × 2 m, with Laishanmi configured as the pollinizer at a ratio of 4:1. Each greenhouse was planted with 3 rows, 50 plants per row. Before planting, dead fibrous roots were cut off, and the roots were dipped in mud slurry. After frost, water was applied in time, the tree rows were covered with plastic film, and the trunks were headed at a height of 25-30 cm.

2.2 Tree promotion and control: In April, May, and June, fertilizer, water, and greenhouse temperature management were strengthened to promote rapid canopy growth, while in July and August, canopy growth was controlled and flower formation was promoted. At the end of February of the planting year, one thawing irrigation was applied; in early March, the greenhouse was covered and the tree disks were covered with plastic film. After covering, the greenhouse temperature was controlled at 16-20°C. In mid-March, the temperature was raised and controlled at 18-28°C, with humidity at 75%-85%. In early May, the greenhouse film was removed. During the rapid shoot growth period, 0.1 kg of potassium sulfate compound fertilizer was applied per plant, followed by under-film irrigation, and 0.3% urea + 0.5% monopotassium phosphate was sprayed on the leaves 2-3 times every 15 days to promote vigorous early growth of the tree. In mid-May, when new shoots reached 30 cm, branches were bent to about 85°, and pinching was carried out at the same time to promote secondary shoots. At the end of July and beginning of August, 15% PP333 at 200 times dilution was sprayed on the leaves, and 10 days later, 200 times PP333 + 300 times monopotassium phosphate was sprayed again. For individual trees with excessive growth, in mid-August, according to tree vigor, 0.5-1 g per plant of PP333 was applied to the soil to control excessive vegetative growth and promote flower bud formation.

2.3 Fertilizer and water management: For mature trees, 8000 kg of organic fertilizer was applied per mu each autumn, mainly decomposed human and livestock manure, barnyard manure, and cake fertilizer, with additional topdressing during the growing season. Before bud break, 0.5 kg per plant of potassium sulfate compound fertilizer was applied; at the beginning of new shoot growth, 0.5% monopotassium phosphate + 0.3% photosynthetic microfertilizer was sprayed on the leaves; during fruit enlargement, 0.5 kg per plant of diammonium phosphate was applied as topdressing; during the pit-hardening stage, 0.5 kg per plant of potassium phosphate compound fertilizer or special fertilizer for fruit trees was applied. Once a year before the soil froze, one winter irrigation was applied, and after each soil fertilization, under-film irrigation was carried out.

2.4 Flower and Fruit Management

2.4.1 Delayed flowering: Starting from the second year after planting, a method of covering the greenhouse twice a year was used. The first covering was in early February. After covering, straw mats and 70% shade netting were laid over the greenhouse, and the greenhouse temperature was controlled at 3-16°C. At the same time, in mid-March, ditches 60 cm deep and 20 cm wide were dug around the greenhouse and filled with insulation boards to block soil heat conduction, lower the greenhouse temperature, and achieve the purpose of delaying flowering. In early April, the greenhouse film was removed. From 7 to 10 days before film removal, the greenhouse temperature was controlled at 15-26°C.

2.4.2 Flower and fruit thinning and bagging: Flower and fruit thinning was carried out strictly to control the fruit load. When flower buds showed red, upper-position flowers, deformed flowers, diseased and insect-damaged flowers, and pruning-cut flowers were removed, while flower buds on both sides of the middle part of the branch were retained. A 0.2%-0.3% borax spray was applied to increase fruit set. During the rapid new shoot growth period, fruit thinning was carried out, leaving one single fruit every 20-25 cm, or leaving 1-2 fruits on short fruiting branches, 2-3 fruits on medium fruiting branches, 3-4 fruits on long fruiting branches, and 1 or no fruit on flower-bundle fruiting branches. The yield per tree at full production was controlled at 5-7 kg. In early to mid-June, double-layer paper bags were applied, and the bags were removed 7-10 days before fruit ripening.

2.5 Training and Pruning

The tree form adopted was the spindle shape. Mature trees were 2-2.5 m tall with a trunk height of 30-40 cm. After heading, one shoot was tied straight as the central leader extension. About 10 scaffold fruiting branches were arranged alternately at intervals of 20-30 cm along the central leader. During summer pruning, 3-4 were heavily renewed and 5-6 branch groups were retained to maintain the leaf area of the tree, rotating them year by year to develop fruiting branch groups. For trees in the early fruiting stage, scaffold branches were bent and pinched. When scaffold branches reached 25-30 cm, pinching was carried out continuously to promote secondary short shoots. At the same time, combined with branch bending, PP333 was sprayed to strictly control excessive vegetative growth. During winter pruning, excess long fruiting branches, overlapping branches, and diseased and insect-damaged branches were removed. For trees in full production, pruning methods mainly included heading back extension branches, heavily cutting water sprouts, leaving vigorous shoots unpruned, and renewing or removing aged fruiting branches to prevent the fruiting zone from moving upward and outward.

2.6 Greenhouse covering, temperature regulation, frost prevention, and leaf protection management

In early September, the greenhouse was covered for the second time to prevent early frost damage to the trees, without covering straw mats. After covering, the greenhouse temperature was comparable to the outside temperature, maintained at 21-27°C during the day and 16-20°C at night, with relative humidity of 60%-65%. After 3-5 days, the greenhouse temperature needed to be lower than the outside temperature in order to extend the fruit-holding time, with daytime temperature at 20-24°C, nighttime temperature at 12-18°C, and relative humidity at 65%-70%. The greenhouse surface was cleaned to increase light inside. During 3 consecutive cloudy days, greenhouse supplemental lights were used at 100 W per square meter to increase light for 4 h per day, and 0.3% photosynthetic microfertilizer was sprayed on the leaves to promote normal photosynthesis and improve photosynthetic efficiency. At the same time, the plastic film was removed, and 1000 kg per mu of decomposed chicken manure was applied, then turned and raked once every 5 days to increase the carbon dioxide concentration in the greenhouse.

2.7 Harvesting and film removal

Late October was the harvest period. According to market demand, temperature was lowered and humidity increased at the appropriate time to maintain the fruit-holding time. After harvesting ended, ventilation was carried out day and night, and the film was removed after 5 days. After film removal, fertilization, irrigation, pruning, and pest and disease control were carried out to strengthen tree vigor and develop new fruiting branches.

2.8 Pest and disease control

Before bud break, 3-5 degrees Baume lime sulfur mixture was sprayed for prevention. After petal fall, 10% imidacloprid wettable powder at 800 times dilution was sprayed to control aphids, leaf miners, and leaf-rolling insects. During the new shoot growth period, 80% Dacotech M45 at 800 times dilution + 1% abamectin emulsifiable concentrate at 5000 times dilution + 25% diflubenzuron at 1000 times dilution was sprayed to control shot hole disease, aphids, oriental fruit moth, leaf-rolling insects, spider mites, and other pests and diseases. Before bagging, 80% Dacotech M45 at 800 times dilution + 85% abamectin-diflubenzuron at 1000 times dilution + amino acid calcium was sprayed for insect control, disease control, and calcium supplementation. During the period when new shoot growth stopped, 65% zineb at 500 times dilution + BT emulsion at 800 times dilution + 10% polyoxin at 1000 times dilution was sprayed over the whole tree to control anthracnose, brown rot, shot hole disease, and others. For individual chlorotic trees, 6% Rui'en No. 1 (Yelüling) was applied as a root drench at 15-20 g per plant.