Detailed Explanation of Key Techniques for Early-Maturing Protected Grape Cultivation

Protected grape cultivation is divided into early-maturing cultivation, delayed cultivation and rain-shelter cultivation. In Hengshui, early-maturing cultivation for an earlier market is dominant, and because of many years of experience in growing protected vegetables, protected grapes have developed very rapidly.

I. Variety Selection

Generally, early-maturing varieties suitable for short-spur pruning, with low chilling requirements, easy flower bud formation, and tolerance to high temperature and high humidity in the greenhouse are chosen, such as Victoria, Fujiminori, Golden Finger, Centennial Seedless, and Red Seedless.

II. Selection of Site and Cultivation Method

To facilitate light exposure, the site should be sheltered from wind and facing the sun, with no tall obstructing objects. The soil should preferably be well-aerated sandy loam, and the terrain flat. Never establish a vineyard on heavily saline-alkali land, low-lying land or replanted land. Cultivation methods include plastic greenhouses and solar greenhouses; in the Hengshui area, plastic greenhouses are mostly used.

III. Environmental Control Requirements

1. Dormancy period.

Greenhouse covering and pre-cooling: After leaf fall, grapes must undergo a certain period of low temperature to break dormancy. Early-maturing varieties generally need 800-1000 hours at 0°C-7°C to successfully complete natural dormancy and then sprout, grow, flower and set fruit normally. To make grapes sprout earlier, the greenhouse must be covered earlier; covering should be done when the outside minimum temperature stays below 7°C for 7 consecutive days. In the Hengshui area, covering is generally done from late October to early November, with straw curtains laid over the greenhouse film. At night, uncover the straw curtains and open the ventilation openings to let cold air in; during the day, cover the straw curtains and close the ventilation openings to maintain low temperature inside the greenhouse, keeping the air temperature at 2°C-7°C and air humidity at 75%-80%, so as to satisfy the chilling requirement of the grapes and pass through dormancy as quickly as possible; natural dormancy can be completed after about 35 days.

Chemical dormancy breaking: To make grape plants sprout uniformly, chemical dormancy breaking is generally carried out in mid-December. Common agents include calcium cyanamide and hydrogen cyanamide. The concentration for calcium cyanamide is 15%-18%, and for hydrogen cyanamide 1.8%. Use a brush or cotton ball dipped in the solution to apply it to the winter buds; do not apply it to the top 1-2 buds of the shoot, to avoid the influence of apical dominance. After 20 days, the buds begin to sprout.

2. Growth period.

Temperature regulation: 10-15 days after winter pruning is completed, start raising the temperature to force buds, and add a second greenhouse layer for heating. Temperature should be raised slowly in the early stage; otherwise the shoots will dry out or flower bud differentiation will be affected, leading to reduced yield. During the bud-forcing period, in early December, uncover the straw curtains during the day and cover them at night. Inside the greenhouse, the temperature in the first week should be 15°C-18°C during the day and 5°C-8°C at night; in the second week, 15°C-20°C during the day and 6°C-10°C at night; from the third week until sprouting, 20°C-23°C during the day and 12°C-15°C at night. During the new shoot growth period, the daytime temperature should be controlled at 25°C-27°C, and at night 14°C, not lower than 10°C. If the temperature is too high at noon, cover with straw curtains to shade and cool down; if the temperature is too low at night, use heating to raise the temperature. During the flowering period, avoid excessively high daytime temperatures and excessively low nighttime temperatures. Keep it at 24°C-25°C during the day, with a maximum not exceeding 30°C. If the daytime temperature is too high, pollen viability decreases and the metabolic rate accelerates, making fruit set difficult and causing severe flower and fruit drop. At night, 15°C-18°C. During the fruit development period, starting from the young fruit stage, 25°C-28°C during the day and 20°C-23°C at night, preferably not below 20°C. During the coloring and ripening period, 18°C-30°C during the day and 15°C-17°C at night. A large day-night temperature difference favors sugar accumulation.

Humidity regulation: During the bud-forcing period, the relative air humidity should be above 85%, and the relative soil humidity 75%. During the new shoot growth period, the relative air humidity should be 65%, and the relative soil humidity 70%. During the flowering period, the relative air humidity should be 60%, and the relative soil humidity 70%. If humidity is too high during flowering, nutrients are consumed, flower bud differentiation is affected, and leaf transpiration is hindered, affecting root uptake and utilization of mineral elements; if too low, the stigma dries out, affecting pollination, fertilization and fruit set. During the berry development period, the relative air humidity should be 65%, and the relative soil humidity 75%; during the coloring and ripening period, the relative air humidity should be 55%, and the relative soil humidity 60%. The measure to reduce air humidity in the protected facility is ventilation. After sprouting, once the soil temperature rises during the bud emergence period, cover with black drip-free plastic film, which can reduce water evaporation from the soil surface and effectively lower indoor air humidity.

Light regulation: The blocking of light by the greenhouse film causes insufficient light, which becomes a bottleneck constraining greenhouse cultivation. Choosing blue drip-free plastic film and laying silver reflective film on the walls inside the greenhouse can increase the illuminated area.

Carbon dioxide regulation: In a closed greenhouse, the carbon dioxide concentration in the air is significantly lower than in the natural environment, which is unfavorable for photosynthesis. Starting when new shoots grow to 20 cm, a carbon dioxide generator can be used to release carbon dioxide, supplementing 1000-1200 grams per mu per day for 25 consecutive days, which can significantly increase the soluble solids content of the fruit and raise fruit yield. The method of artificially applying carbon dioxide gas fertilizer is to use the reaction of ammonium bicarbonate with dilute sulfuric acid to produce carbon dioxide directly applied in the facility; the ammonium sulfate produced at the same time can also be used as chemical fertilizer. Inside the greenhouse, every 10 m, hang 1 plastic bucket at a height of 2 m, pour in an appropriate amount of dilute sulfuric acid, and add ammonium bicarbonate at any time to release carbon dioxide gas. Carbon dioxide should especially be applied before and after flowering, during young fruit swelling, and during the berry coloring and ripening period.

IV. Training and Pruning

Generally, a trellis or hedge system is used. Pruning time is from after leaf fall to before bleeding, that is, from late November to the end of January of the following year. After winter pruning, leave 3600 fruiting canes per mu, and regulate the number of shoots and clusters retained through bud thinning and shoot selection. Pinch the growing point of fruiting shoots after 10 leaves, and pinch vegetative shoots after 15 leaves; pinch the top secondary shoots of fruiting shoots and vegetative shoots after 8 leaves, and pinch other secondary shoots after 5 leaves. Girdling before and after flowering can increase the fruit set rate; girdling before fruit ripening and coloring can promote fruit ripening and improve quality; girdling before fruit ripening is best done 15 days before harvest.