Fertilizer damage can occur in various forms, depending on the type and method of application. Understanding these issues is crucial for preventing harm to crops, especially tomatoes.
First, there are several types of fertilizer-related injuries:
1. **Ammonia Toxicity**: Excessive use of ammonium-based fertilizers can lead to ammonia buildup. When ammonia concentration exceeds 5 ml/l, it causes water-soaked spots on leaves, leading to cell dehydration and death. At higher levels, such as 40 ml/l, severe damage occurs—tissue necrosis, disintegration of mesophyll, and brown lesions between leaf veins.
2. **High Salt Concentration**: Applying too much fertilizer or manure can raise soil salt levels beyond 3000 ml/l. This makes it difficult for plants to absorb water and nutrients, increasing their resistance to cell penetration and causing stress.
3. **Dry Fertilizer Application**: Directly applying dry fertilizer to plant roots can be harmful. The root zone, particularly the root hairs, has the strongest absorption capacity. However, chemical fertilizers with high concentrations act quickly but can cause serious damage when applied directly.
4. **Uncomposted Organic Manure**: Using fresh animal waste without proper decomposition can release organic acids and heat during breakdown, which harms plant roots and affects growth.
5. **Excess Fertilization**: Over-application of fertilizers or human urine often leads to excessive ammonia, creating a "salt barrier" in the soil. This can burn roots, kill seeds, and reduce crop yield.
Second, **physiological fertilizer injury** occurs due to imbalances in ion uptake. Common cases include:
1. **Ammonia Poisoning**: Excess ammonium in the soil can cause plants to absorb too much ammonia, disrupting photosynthesis and leading to yellowing leaves and stunted growth.
2. **Nitrite Accumulation**: Overuse of nitrogenous fertilizers may result in nitrite buildup, causing nitrous acid poisoning. Roots turn brown, leaves yellow, and calcium deficiency may develop in tomatoes.
3. **Ion Antagonism**: Excessive phosphate can interfere with calcium and trace element absorption, leading to problems like tomato blossom end rot. Similarly, potassium can block calcium and magnesium uptake, causing physiological disorders.
To prevent fertilizer damage:
1. Conduct **soil testing** and apply fertilizers based on plant needs and soil conditions.
2. Use **balanced fertilization**, combining nitrogen, phosphorus, and potassium according to the growth stage of the tomato.
3. Increase **organic matter** in the soil. Composting improves soil structure, increases cation exchange capacity, and reduces the risk of fertilizer burn.
4. Improve **fertilizer application techniques**, such as layering or deep placement, to avoid surface exposure. Watering after fertilization helps dissolve the nutrients and lower concentration.
5. Consider using **bio-fertilizers** alongside organic materials to enhance nutrient availability and improve crop quality.
These practices help maintain soil health, promote sustainable farming, and ensure better yields and fruit quality.
Author unit: Agricultural Service Station, Taitai Township, Taitai County
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