Fertilizer damage can occur in various forms, and understanding the different types is essential for proper prevention and management. Here's a comprehensive overview of fertilizer-related issues and how to address them.
First, let's explore the main types of fertilizer damage:
1. **Toxic Fertilizer Damage**
This occurs when excessive amounts of ammonium nitrogen are applied. When ammonium decomposes into ammonia, especially in poorly ventilated areas, it can cause water-soaked spots on leaves. At concentrations above 5 ml/l, the cells lose water and die, leading to necrotic spots. If ammonia levels reach 40 ml/l, severe damage to tomato plants can occur, including tissue necrosis in shoots, disintegration of mesophyll between stems and leaves, and chlorophyll breakdown, resulting in brown lesions between veins.
2. **High Salt Concentration Injury**
Applying too much fertilizer or human waste can lead to high soil salinity. When the total salt concentration exceeds 3000 ml/l, the plant’s ability to absorb nutrients and water is severely hindered. The increased osmotic pressure makes it difficult for roots to take up moisture, causing physiological stress.
3. **Dry Application of Fertilizers**
Directly applying dry fertilizers to plant roots can be harmful. The root zone, especially the root hairs, has the strongest absorption capacity. However, chemical fertilizers with high concentrations can cause immediate damage, leading to root burn and reduced growth.
4. **Uncomposted Organic Manure**
Fresh animal manure that hasn’t been properly composted releases organic acids and heat during decomposition. This can harm plant roots and negatively affect overall plant health.
5. **Excessive Fertilization**
Over-application of fertilizers or human urine often leads to salt buildup in the soil. This creates a concentration barrier, which can burn roots and even kill seeds in extreme cases.
Second, **physiological injury from fertilizer imbalance** is another common issue. This happens when the ion balance within the plant is disrupted due to improper fertilization. Common scenarios include:
1. **Ammonia Toxicity**
Excess ammonium in the soil can lead to ammonia poisoning, disrupting normal photosynthesis and causing leaf discoloration and stunted growth.
2. **Nitrogen Overload**
Too much nitrogen fertilizer can result in nitrite accumulation, leading to nitrous acid toxicity. Roots may turn brown, and leaves yellow. Excess nitrogen can also reduce calcium uptake, affecting fruit quality in tomatoes.
3. **Ion Antagonism**
Overuse of phosphate fertilizer can interfere with calcium and trace element absorption, especially in alkaline soils. This can lead to blossom end rot in tomatoes. Similarly, excess potassium can hinder calcium and magnesium uptake, contributing to various physiological disorders.
**Prevention and Treatment Measures:**
1. **Soil Testing and Balanced Fertilization**
Conduct regular soil tests to determine nutrient needs and apply fertilizers accordingly. Avoid over-fertilizing based on assumptions.
2. **Rational Use of Chemical Fertilizers**
Combine nitrogen, phosphorus, and potassium fertilizers as needed. Adjust application rates according to the growth stage of the tomato plant and avoid using single-nutrient fertilizers excessively.
3. **Increase Organic Matter**
Incorporating organic fertilizers improves soil structure and increases its buffering capacity. As organic matter decomposes, it forms colloids that help retain nutrients and prevent salt buildup. Combining with bio-fertilizers can further enhance nutrient availability and improve crop quality.
4. **Improve Fertilization Techniques**
Use methods like layered or deep placement to avoid surface exposure. Watering after fertilization helps dissolve the nutrients and reduce their concentration, making them more accessible to plants.
By adopting these practices, farmers can significantly reduce the risk of fertilizer damage and promote healthier, more productive crops.
Author unit: Taitai Township Agricultural Service Station, Taitai County.
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