Greenhouse moisture management involves the effective control of humidity levels within the greenhouse environment. The primary indicator used to measure and evaluate environmental moisture is air relative humidity. Maintaining optimal humidity levels is crucial for plant health, especially in tomato cultivation.
In a greenhouse, air humidity tends to be high, particularly during winter when ventilation is limited. Relative humidity can often exceed 80%–90%, reaching 100% at night when the air becomes saturated. This high humidity is influenced by several factors, including soil moisture, greenhouse structure, and weather conditions. For instance, higher soil moisture increases air humidity, while better-ventilated greenhouses tend to have lower humidity levels. Smaller greenhouses generally have higher humidity compared to larger ones, and sunny days usually result in lower humidity levels.
Irrigation plays a key role in controlling air humidity. Traditional surface irrigation methods like furrow or basin irrigation increase humidity, whereas modern techniques such as drip, sub-surface, or infiltration irrigation help maintain stable humidity levels. These methods not only reduce the risk of pests and diseases but also improve water use efficiency.
To manage humidity effectively, several strategies are employed:
1. **Scientific Irrigation**: Minimize the amount and frequency of irrigation to control soil moisture, thereby reducing the source of moisture that contributes to high air humidity.
2. **Ventilation**: Proper ventilation helps reduce temperature and humidity. During warmer seasons, longer and more frequent ventilation is recommended, while in colder months, it should be done briefly and during midday when temperatures are higher.
3. **Plastic Film Mulching**: This practice reduces evaporation, lowers indoor humidity, and increases ground temperature, which benefits root development.
4. **Insulation and Dehumidification**: Increasing greenhouse temperature can significantly reduce relative humidity. For every 1°C rise in temperature, humidity can decrease by approximately 5%.
Soil moisture control is equally important. Tomatoes require a soil moisture content between 60% and 85%, with ideal air humidity ranging from 50% to 65%. Different growth stages have varying moisture needs: germination requires around 80% soil moisture, seedlings and flowering need about 65%, and fruiting stages demand 75%–80%.
Excessive or insufficient moisture can hinder plant growth. Overwatering may lead to root rot and reduced oxygen availability, while underwatering causes wilting and leaf damage. Therefore, proper irrigation scheduling is essential.
**Irrigation Methods**: Drip irrigation under mulch is highly efficient, saving water and maintaining soil structure. Furrow irrigation, when combined with mulching, also helps reduce evaporation. Sprinkler systems are suitable for young plants, while controlled watering is needed during flowering and fruiting.
**Watering Schedule**: Watering frequency depends on the growth stage and environmental conditions. In general, watering is less frequent during cooler months and more frequent during warmer periods. It’s important to avoid overwatering, especially after planting, to prevent flower and fruit drop.
**Determining Watering Time**: The best time to water is early morning when temperatures are cooler. Avoid watering on cloudy or windy days, as this can increase humidity and disease risk. Monitoring seedling behavior and soil temperature helps determine when to irrigate.
By implementing these practices, growers can maintain optimal humidity and moisture levels, leading to healthier plants and higher yields.
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