Greenhouse Vegetable Cultivation Techniques

In recent years, the development of greenhouse vegetables has been rapid, playing an important role in promoting efficient agriculture. Greenhouse vegetable cultivation is a high-input, high-output production method under specific environmental conditions. Due to the unique microclimate in greenhouses, poor ventilation and light transmission, high temperature, and humidity inside the greenhouse, excessive or improper fertilization can lead to soil compaction, imbalance of nutrients, and excessive nitrate and nitrite content in vegetables, posing health risks to consumers. Therefore, when cultivating greenhouse vegetables, the temperature inside the greenhouse should be maintained 2°C to 3°C higher than the upper limit of the crop’s optimum temperature, especially during the deep winter season. How to manage greenhouse vegetable cultivation techniques:

1. Strengthen insulation and prevent cold and freezing. As the climate becomes colder, low temperatures and strong winds often occur, so it is essential to do well in cold protection and insulation to prevent vegetable damage from low temperatures during winter greenhouse management.
2. Multiple covering cultivation techniques are commonly used in production. This includes covering the ground with plastic film to increase soil heat capacity and using grass curtains on the greenhouse film, covered with an additional layer of plastic film to prevent rain from wetting the grass curtains, effectively increasing indoor temperatures. Through multiple covering, the temperature inside the greenhouse can be increased by 3°C to 5°C, effectively preventing cold and maintaining warmth. In the case of severe cold weather, temporary heating measures should be taken (attention should be paid to controlling the temperature, ensuring that the temperature does not rise too high, especially controlling the night temperature).
3. Scientifically hang thermometers. Thermometers in the greenhouse are often hung on the upper part of the plants. During the day, the air temperature at different heights is directly proportional, especially when the plants are dense and tall. Due to the shading effect of branches and leaves, the temperature gradient decreases significantly from the growing point to the ground. Measures to increase light include:
   • Replace old films and keep them clean. High-transmittance agricultural films such as green bamboo EVA film, Taiguang, and Xifeng should be used, and the film surface should be wiped frequently to ensure cleanliness.
   • Cover the ground with white plastic film, not black plastic film, as white plastic film reflects light, increasing the light intensity in the lower part of the plants, while black plastic film absorbs light.
   • Hang reflective curtains on the back wall.
   • Prune and remove leaves in a timely manner to increase light transmission in the field.
4. Reduce humidity. High humidity inside the greenhouse is the main cause of pathogen induction, so it is necessary to reduce humidity inside the greenhouse through the following two methods:
   • Cover the ground with plastic film and cover the operation rows with straw or cover the entire greenhouse with plastic film to reduce soil moisture evaporation and lower greenhouse humidity.
   • Use the method of two-stage ventilation to exhaust moisture from the greenhouse and harmful gases, while increasing the concentration of carbon dioxide in the greenhouse.

There are many types of greenhouse vegetables, but they share common characteristics in terms of fertilization requirements:

1. Requires a large amount of fertilizer and has special nutrient requirements. Greenhouse vegetables prefer nitrate nitrogen, have a high demand for potassium and calcium, and are sensitive to boron and molybdenum. Generally, greenhouse vegetables have a long growth period and high yields, requiring a large amount of fertilizer, several times that of cereal crops. For example, the average nitrogen uptake of vegetables is 5.4 times that of wheat, phosphorus uptake is 1.2 times that of wheat, potassium uptake is 2.9 times that of wheat, calcium uptake is 5.3 times that of wheat, and magnesium uptake is 1.5 times that of wheat.
2. High soil solution concentration. The relatively closed environment of the greenhouse is rarely affected by rainwater and irrigation water leaching. Most of the fertilizer applied remains in the soil. Over time, the soil solution concentration becomes too high, causing nutrients and moisture to move outward from the roots, leading to physiological diseases such as nutrient deficiencies.
3. Heavy root burden. Greenhouse vegetable root systems are small, shallowly distributed, and have a small absorption range. In addition, greenhouse vegetables grow quickly and absorb nutrients intensively. When the soil temperature is low, the root absorption capacity is weak, so sufficient soil nutrient supply is required to meet the growth and development needs of greenhouse vegetables.

Misconceptions about greenhouse vegetable fertilization include:

1. Applying unripe organic fertilizer. Organic fertilizers have a low carbon-nitrogen ratio, decompose quickly, and can locally produce high temperatures and high concentrations of ammonia and organic acids, which can easily cause root burns. Therefore, organic fertilizers should be used after high-temperature fermentation.
2. Excessive application of nitrogen fertilizer. Relying solely on nitrogen fertilizer supplementation can cause soil phosphorus and potassium fertilizers and micronutrients to decrease as the greenhouse ages, leading to an imbalance in soil nutrient proportions and various diseases, such as celery stem cracking and tomato blossom-end rot.
3. Excessive fertilizer application. Greenhouse vegetables often apply excessive amounts of fertilizer, especially high doses of chemical fertilizers, which can easily cause fertilizer damage. This results in difficulty for crop roots to absorb water, seedling wilting, leaf deformities, and even crop death.
4. Biased application of chemical fertilizers reduces nutrient utilization. Excessive amounts of certain nutrients can produce antagonistic effects, causing crops to exhibit deficiency symptoms. For example, excessive nitrogen can lead to calcium deficiency, causing cabbage to have heartburn; high soil salt concentrations inhibit strawberry calcium absorption, leading to physiological calcium deficiency; excessive potassium reduces the effectiveness of calcium, zinc, and boron fertilizers; excessive phosphorus reduces the effectiveness of calcium, zinc, and boron fertilizers.
5. Long-term application of chloride-containing fertilizers. Chloride can reduce starch content in vegetables, deteriorate vegetable quality, reduce yield, and remain in the soil, leading to soil acidification and calcium loss, resulting in compaction.
6. Improper fertilization methods can also harm plants. For example, when applying high-concentration compound fertilizer, it should be applied near the roots to prevent scorching of vegetable seedlings.

Scientific fertilization is the key to achieving high-quality and high-yield greenhouse vegetables.

The principles of greenhouse vegetable fertilization are: main base fertilizer, supplementary topdressing; main organic fertilizer, supplementary chemical fertilizer; rational application of nitrogen, phosphorus, and potassium fertilizers, supplemented with micronutrients.

1. Mainly apply base fertilizer, supplemented with topdressing. Base fertilizer is best applied a week before planting vegetables, mixed evenly with the soil. Topdressing should follow the principles of thin application and frequent application. It can be applied in trenches or pits 7-10 cm away from the plants. After topdressing, cover the soil and water it in time. Avoid directly sprinkling fertilizer on the ground or plants to prevent fertilizer volatilization or burning of vegetable seedlings.
2. Organic fertilizer is the mainstay, supplemented with chemical fertilizer. Increasing organic fertilizer can improve soil structure and increase soil water and fertilizer retention capacity. At the same time, the decomposition of organic fertilizers produces carbon dioxide, which can compensate for the lack of carbon dioxide in the greenhouse.
3. Apply nitrogen, phosphorus, and potassium fertilizers reasonably and supplement with micronutrients.