High-Yield Cultivation Techniques for Blackberry in Solar Greenhouses

The blackberry is native to the United States and belongs to the Rosaceae family; it is a perennial vine fruit tree. Its fruit clusters are large, the fruit is conical, the skin is black, the average cluster weight is 500g, the average single fruit weight is 10.8g, the largest single fruit weight is 16.9g, the soluble solids content is 12.8%, the titratable acidity is 1.4%, vitamin C 140.7υg/g. The berries are sweet and sour, pleasant to the taste, with a slight aroma, of extremely high quality, high-yielding and disease-resistant, and of relatively high commercial value. It was introduced to Laiwu, Shandong in 2001, and from 2003 to 2006, cultivation trials were conducted in solar greenhouses at the core demonstration orchard of the Laiwu Municipal Institute of Agricultural Sciences of Shandong Province and the Forestry Science and Technology Demonstration Orchard in Niuquan Town, Laicheng District, where it performed well. The trial results are summarized as follows.

Test Site Conditions and Greenhouse Structure

The average annual temperature of the test site is 12.5°C, the average January temperature is -2.8°C, the annual precipitation is 760mm, the frost-free period is 203 days, the average annual effective accumulated temperature is 4264.5°C, and the average annual sunshine duration is 2629.2h. The soil is plain sandy loam with a thick soil layer, organic matter content of 0.65%-0.90%, and pH 6.5-7.0. The greenhouse has a steel frame structure, facing north and south, extending in an east-west direction, with an east-west length of 85m, a north-south width of 9m, a front height of 1.5m, a ridge height of 3.5m, and a rear wall height of 2.5m. The wall thickness is 1.0m and it is of a brick-and-earth composite structure. The rear wall has 16 ventilation windows measuring 60cm square. The greenhouse film is polyethylene anti-drip film, covered with straw curtains, with an automatic curtain-rolling machine installed on the roof. Inside the greenhouse are drip irrigation equipment, fluorescent lamps (for supplemental lighting), a coal-fired heating system (for heating), and a carbon dioxide gas fertilizer generator.

Yield and Benefits of the Test Greenhouse In the spring of 2003, strong blackberry seedlings were planted, and the greenhouse was covered that same year. In mid-May of the following year, the yield reached 1000kg per 667 square meters; in 2005, the average yield reached 1500kg per 667 square meters; in 2006, the average yield reached 1900kg per 667 square meters. The average price over 3 years was 26 yuan, and the output value per 667 square meters in the 2nd, 3rd, and 4th years after planting was 26000 yuan, 39000 yuan, and 49400 yuan respectively. The total gross income per 667 square meters of the test greenhouse over the first 4 years was 114400 yuan, and the economic benefits were quite significant.

Main Cultivation Techniques

Planting

Plant in a north-south direction, with a plant spacing of 1m×1.5m. Before planting, dig a planting trench 1m wide and 60-70cm deep, fill the bottom of the trench with 15-20cm of corn stalks, sprinkle a small amount of urea on top, then calculate the amount of fertilizer according to the standard of 2500kg of high-quality chicken manure per 667 square meters, mix thoroughly with the topsoil and backfill, then water to settle. In early April, dig planting holes 30cm wide and 30cm deep in the planting trench. Soak the roots of the seedlings in 50mg/L ABT No. 3 rooting powder for 5min before planting. After planting, water and cover with black plastic film.

Fertilizer and Water Management

In early to mid-September each year, apply 2500kg of high-quality chicken manure and 50kg of nitrogen-phosphorus-potassium compound fertilizer per 667 square meters. During the rapid growth period of new shoots, apply 50kg of urea per 667 square meters as a top dressing, and spray 0.2% urea once every 10 days, for 3 consecutive sprays. Spray 0.3% borax 3-5 days before flowering, and then spray 0.2%-0.3% zinc sulfate 1-2 days later, which can greatly reduce the proportion of small fruits. During the fruit expansion period, apply 50kg of diammonium phosphate. In addition, combined with pesticide spraying, spray 0.3% monopotassium phosphate or 500 times photosynthetic micro-fertilizer or 800-1000 times vitality essence once every 10 days, for 3 consecutive sprays, to supplement tree nutrition.

Irrigation is carried out in conjunction with fertilization, generally including the following times. Winter water: this irrigation can use the flood irrigation method to keep the 60-80cm soil layer moist, so as to supply the water needs of the tree during dormancy; the time is after the tree leaves fall and before the greenhouse film is covered. Early new shoot growth period: if the soil is severely short of water, irrigate once heavily to make up for it; never irrigate lightly and frequently. Pre-flowering irrigation: use drip irrigation; this irrigation makes the flower buds plump and full, maintains a certain amount of nutrients and moisture in the flower buds, and lays a good foundation for good pollination and improved fruit set rate. Young fruit irrigation: use drip irrigation, at the time when the young fruits are set after flower drop; this period is a stage of rapid young fruit development, requiring a lot of nutrients and water. In order to reduce fruit drop and stabilize yield, irrigation is key; irrigate lightly and frequently, with 15-20mm of water once a week. Berry coloring and ripening period: generally do not irrigate.

Training and Pruning

Blackberry training techniques generally follow the trellis training method used for grapes. In the year of planting, when the young seedlings sprout, keep 3-4 vigorously growing new shoots. When the canes grow to 30-40cm, tie them upward, and prune the rest from the base; in the future they will form 3-4 main branches. Cultivate 2-3 side branches on each main branch. Main branches are generally pinched at 1.0-1.2m, side branches are generally pinched when they reach 50cm, and vegetative branches are generally pinched after leaving 5-7 leaves. At the beginning of flowering, vegetative branches should be heavily pinched to reduce the consumption of tree nutrients, ensure uniform flowering, and make flowering neat. After fruit harvest, remove the fruiting branches from the base and cultivate new main branches and fruiting branches for the following year. During winter pruning, cut off senescent main trunk branches, diseased and pest-infested branches, thin and weak branches, and excessively dense branches. The following year, keep main branches again; generally 9-12 vigorous side branches can be kept per plant, with branch length controlled within 1.0-1.2m.

Temperature and Humidity Management

Blackberry requires 1000h at temperatures below 7.2°C to pass natural dormancy. Therefore, in mid-November, the film should be covered and straw curtains put on, so that no light enters the greenhouse, and all ventilation openings should be opened at night, regulating the greenhouse temperature at -2 to 7.2°C. This can both increase the amount of low temperature and protect the plants from freezing damage. After about 30 days, that is, in mid-December, the temperature can be gradually raised. During the day, first lift 1/3 of the straw curtains; after 5 days, lift 2/3 of the straw curtains during the day; after another 5 days, lift them all during the day.

Starting from the beginning of heating to promote bud break, low-temperature management should be implemented in the first week, maintaining about 20°C during the day and 10-15°C at night. After that, gradually raise the temperature until bud break and sprouting, when it can rise to 28-30°C during the day and remain 15-20°C at night, with a minimum not lower than 5°C. This period is the one with the greatest water demand in the blackberry growth cycle, requiring sufficient irrigation, generally irrigating twice with 30mm of water, and keeping the greenhouse doors and windows tightly closed to maintain relative air humidity above 80%. If daytime humidity is low, spray water onto the canes to keep them under conditions of a certain degree of high temperature and high humidity, promoting early bud emergence.

In the early stage of new shoot growth, implement low-temperature and low-humidity management. Control the daytime temperature at 25-28°C and keep it at 15°C at night, with a minimum not lower than 10°C. While strictly controlling irrigation, also strictly control air humidity, maintaining it at about 60%.

Before and after flowering, a relatively high temperature is needed. Maintain about 28°C during the day and 16-18°C at night, with a minimum not lower than 15°C, and keep air humidity at about 50%.

During the young fruit expansion period, maintain the daytime temperature at 25-28°C, not exceeding 30°C; the night temperature can be kept at 18-20°C, but not exceeding 20°C. Humidity management can be left to nature.

During the berry coloring and ripening period, increase the day-night temperature difference to enhance sugar accumulation, with 28-30°C during the day and 16-18°C or lower at night. Supplemental Lighting and Increased Application of Carbon Dioxide Gas Fertilizer

Insufficient light and poor light quality are common problems in the cultivation of blackberry in winter warm solar greenhouses. Therefore, supplemental lighting is needed: supplement 1h per day before fruit set, and 2h per day after fruit set. Fluorescent lamps can be used for supplemental lighting, with the lamps about 50cm away from the tree.

Supplementing carbon dioxide gas fertilizer is a technique with extremely significant yield-increasing effects in protected cultivation of blackberry, generally increasing yield by 25%-30%, and the effect is even more obvious for solar greenhouse production. The best time to apply carbon dioxide gas fertilizer is generally shortly after sunrise, that is, 8 o'clock from late January to late February, 6:30 to 7 o'clock in March to April, and around 6 o'clock in May. The application period is most effective during the rapid fruit expansion period. The application concentration is generally about 1000υL/L. Excessive release will harm the leaves, causing leaf margin scorch, which is unfavorable for photosynthesis and harmful to human health. In addition, in greenhouses where carbon dioxide fertilization is carried out, the daytime temperature should be correspondingly increased by 3-4°C, and the nighttime temperature variation range should be slightly increased, slightly higher in the first half of the night and slightly lower in the second half, to improve the fertilization effect. On cloudy, cold wave, and rainy (snowy) days, because the temperature is low, light is poor, and photosynthesis is weak, carbon dioxide fertilization is generally not carried out.

Flower and Fruit Management

Two days before blackberry flowering, place bees in the greenhouse to prepare for pollination during the flowering period and improve the fruit set rate. Spray 0.5% borax plus 0.2% urea at the early flowering stage; spray 5-10mg/L gibberellin plus 0.2% monopotassium phosphate at the full flowering stage; both can improve the fruit set rate. At the same time, during the flowering period, remove excessive flower clusters; one week after flower drop, thin the fruit, leaving 20-30 fruits per cluster, with no more than 40 at most. To prevent pre-harvest fruit drop, spray 70mg naphthaleneacetic acid twice 30 days before harvest, which can effectively reduce fruit drop. During the fruit turning black stage, lay reflective film on the entire greenhouse floor, which helps increase soil temperature, reduce humidity in the greenhouse, promote fruit development, improve coloring, and make the fruit mature 6-8 days earlier. Spraying 0.5% glucose solution during the fruit expansion period can significantly increase fruit sugar content, reduce acidity, and improve fruit quality. 10 days before fruit ripening, remove vigorous new shoots in the upper canopy that seriously shade the fruit, to facilitate fruit coloring. Fruit clusters treated this way have large fruits, good color, and excellent quality. Control the yield per 667 square meters within 2000kg to achieve high and stable yields every year.

Pest and Disease Control

Pests and diseases are relatively mild in greenhouse cultivation of blackberry. Spray 5°Be lime sulfur mixture once before sprouting. If gray mold and root rot occur, use 1000 times procymidone or 50% carbendazim 500-800 times solution for control.