Eggplants grown in greenhouses typically show strong growth and high yields during the first year. However, in the spring of the second year, their growth becomes weak and yield drops significantly. This is a common issue known as premature aging of the plant’s growth and development.
The main causes of this early decline include several factors. First, seedlings are often raised between June and July when temperatures are high and humidity is high. Without proper shading or cooling, the seedlings tend to become leggy, with weak root systems that struggle to absorb nutrients effectively. Second, excessive use of nitrogen-rich chemical fertilizers during the seedling stage can worsen this problem by promoting leafy growth at the expense of root development.
After planting, many growers apply large amounts of chemical fertilizers in greenhouses. A typical base fertilizer might be 100–150 kg of compound fertilizer per acre, with additional top-dressing. Over the course of a year, more than 300 kg of chemical fertilizers may be used, which can hinder the development of a deep and extensive root system. Poor root growth limits nutrient uptake, leading to weaker plants over time.
Soil preparation is another key factor. Some greenhouse farmers use shallow tilling methods, such as rotary plows that only go 10 cm deep or manual plowing that doesn't exceed 20 cm. This shallow tilling, combined with heavy fertilizer use, leads to compacted soil and poor structure. Eggplants require deep, loose soil for healthy root growth, and shallow, hard-packed soil restricts root expansion, reducing the plant's ability to absorb water and nutrients.
Another contributing factor is pruning practices. In greenhouses, growers often use a double-pruning method to increase early yield, which differs from the multi-pruning approach used in open fields. This aggressive pruning reduces shoot and leaf growth, which in turn limits root development. As the plant grows taller, the distance for water and nutrient transport increases, affecting overall growth and yield later on.
Mulching is also a factor. While mulch helps maintain surface soil moisture, it can prevent roots from growing deeper. Shallow roots absorb most of the available nutrients, leading to deficiencies later in the season. This can negatively impact the plant's health and productivity.
To prevent this premature decline, several measures can be taken. Shade and cooling should be used during the seedling stage to avoid legginess and encourage strong root development. Fertilizer application should be reduced, especially nitrogen, and organic matter should be sufficient to support growth without synthetic inputs.
When planting, the amount of chemical fertilizer used as a base should be limited—around 30–50 kg of compound fertilizer per acre. After planting, root-stimulating treatments can help promote healthy root growth. Before planting, applying a soil conditioner can improve soil structure up to 30–50 cm deep, making it easier for roots to grow and increasing water retention.
During the second year, regular foliar feeding with essential nutrients like potassium, boron, calcium, magnesium, iron, and zinc can help address deficiencies. Spraying these nutrients every 5–10 days at a concentration of about 0.3% can support plant health. Additionally, using a natural plant growth regulator like Alfalfa Shuofeng 481 every 10–20 days can enhance photosynthesis and overall vegetative growth.
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