Comparing with open filed cultivation, greenhouse vegetable has stricter requirement for fertilizer. Improper fertilization can not only cause soil hardening, but also make the nitrate and nitrite content in vegetable become superstandard, which is detrimental to human health. Therefore, we must know what should be noted as far as scientific greenhouse fertilizing.
1. Farmyard manure should be thoroughly decomposed.
Farm manure like crop straw, human waste, livestock and poultry manure should be decomposed before applied, or the germs and insect eggs in them will make disease spread. Chicken manure, especially, should have a high degree of decomposition and be applied in advance. Non-decomposed manure will produce ammonia, polluting air and burning the vegetable seedling.
2. Adopt rational fertilizing method.
Base fertilizer should be early applied and mixed evenly with soil. By deep placement, the using efficiency is raised. Meanwhile, in the deep soil, the air is in anaerobic conditions, the volatilization and nitrification of nitrogen fertilizer is slow, preventing ammonia pollution and reducing nitrate accumulation in vegetables. Dressing should be of more time and small amount each. Foliage spray is highly encouraged, which doesn’t increase soil salinization and acidification.
3. The chemical fertilizer applied should be in proper amount.
Usually vegetables need large amount of nitrogen and potassium. The demand for phosphorus is small. We should control the amount of nitrogen and phosphate fertilizer, increasing potash fertilizer.
High nitrogen content can increase soil solution concentration, basify the soil, slow the growth of crops, and even result in seedling and leaves burning. Overmuch nitrogen fertilizer will also restrain the soil’s absorption for potassium, calcium, magnesium, ferrum, zinc and so on.
Diammonium phosphorus should not be much, otherwise overabundant rapid available phosphorus will restrain the absorption of potash fertilizer. Phosphate is hard to utilize as it can be fixed by reacting with calcium, ferrum and aluminium.
Nitrate nitrogen, chloride, ammonium carbonate and ammonium sulfate should be limited or forbidden to use.
4. Apply appropriate amount of trace element fertilizer.
For vegetables, trace element fertilizer is in small demand but has large impact on its metabolism. The soil in newly-built greenhouse usually lacks trace elements, dehiscent fruit and soft rot is thus easily brought about. So we suggest applying trace element fertilizer in the middle and later stage of vegetables, especially fruit vegetables. Mainly choose calcium, boron and magnesium fertilizer. Foliage sprayed trace element fertilizer should be controlled in amount and not to be applied on leafy vegetables to avoid increasing nitrate content. Besides, vegetables also need Fe, Mn, Zn, Cu, Mo, Cl, etc.
5. Apply ecological organic fertilizer.
Ecological organic fertilizer has rich content of organic matter. It has the effect of nitrogen fixation, phosphate-solubilizing and potassium-solubilizing, and can resolve the pesticide and fertilizer residue. Besides, applying biological-organic compound fertilizer and humic fertilizer can improve soil and increase fertility,creating a favorable environment for the growth of pollution-free vegetable.
6. Apply fertilizer special for vegetable.
Appropriative fertilizer is made according to the characteristics of vegetable and fertilizer. It can significantly increase the yield and quality of greenhouse vegetable.
7. Combining irrigation with fertilizing.
Fertilizing vegetable during soil drought will not give full play to fertilizer efficiency. Meanwhile, the sudden increase in soil solution concentration easily leads up to roots burning phenomenon. So fertilizing for vegetable should be combined with irrigation, more time and small amount each, for flood irrigation would carry away fertilizer applied and nutrients in surface soil, accelerating soil acidification and hardening.