I can't give you a specific time for your question. Let's just say that foliar topdressing should be used flexibly, because foliar topdressing is an auxiliary emergency measure, which is often used when maize element deficiency occurs or root function declines. Then element deficiency may occur in all growth stages of corn. Once the elements are lacking, the yield of horse corn will be affected. Then you have to spray different nutrients according to the principle of supplementing what is lacking, so the time and fertilizer types will be different. The possible element deficiency of corn and the method and time of spraying fertilizer are analyzed below.
First, there is a lack of nitrogen
Nitrogen fertilizer mainly affects the photosynthesis of maize, which is a sensitive crop. When nitrogen is lacking, the plants will be short and thin, the lower leaves will start to turn yellow, and gradually develop upwards, and the leaves will become thinner and yellow.
Corn may be short of nitrogen at that time. In addition to foliar spraying 1% urea solution, it is necessary to do a good job of nitrogen topdressing, otherwise it is difficult to stop the sustainable development of nitrogen deficiency by foliar topdressing alone.
Second, phosphorus deficiency.
Phosphorus can enhance the drought resistance and lodging resistance of maize, a tall crop. When phosphorus is slightly deficient, plants will be dwarfed. When phosphorus is seriously deficient, the leaves turn purple or red in the early stage, and the tip of the leaf dies and turns dark brown. Phosphorus deficiency is most obvious in maize seedlings. If phosphorus is deficient at this time, the ear of corn will bend, the grain rows will be irregular and the baldness will be serious in the later stage. Adequate phosphorus can improve the yield and quality of corn.
Used to control phosphorus deficiency in maize, 0. 1? 0.2% potassium dihydrogen phosphate for remediation, and at the same time do a good job of topdressing phosphorus fertilizer in the soil.
Third, potassium deficiency.
When potassium fertilizer is sufficient, it can promote photosynthesis, promote the absorption of nitrogen and phosphorus by plants, make the leaves strong, make the straw lignified and stout, not prone to lodging, and enhance the disease resistance.
When maize is deficient in potassium, the lower leaves turn yellow from the tip of the leaf along the leaf edge in the early stage, are burnt, the photosynthesis is obviously reduced, the stem is thin, the root growth is inhibited, and it is easy to lodging in the later stage, with small ears, especially sharp tips and severe baldness.
For the prevention and treatment of potassium deficiency in maize, the best method is to prepare sufficient base fertilizer, spray potassium dihydrogen phosphate and other potassium fertilizers in time at seedling stage, and topdressing potassium fertilizers in the soil as soon as possible, otherwise it will be difficult to recover once potassium deficiency occurs.
Fourth, magnesium deficiency
Magnesium plays an important role in photosynthesis, which can promote plant metabolism and respiration. Magnesium deficiency will first appear in maize seedling stage, the upper leaves of seedlings will turn yellow, and even yellow-white stripes will appear between veins, and the tips and edges of old leaves will be purple.
To prevent magnesium deficiency in maize, magnesium fertilizer such as magnesium sulfate should be sprayed in time when seedlings show symptoms. Then applying organic fertilizer or calcium magnesium phosphate fertilizer to the soil can fundamentally solve the problem.
Fifth, iron deficiency.
When plants are deficient in iron, chlorophyll cannot be synthesized, leading to yellowing. The lower leaves of plants often remain green, and the veins of upper leaves lose green or even white, or the whole leaves lose green.
Prevention and treatment of iron deficiency, when symptoms appear and when ferrous sulfate is sprayed, the available concentration is 0. 1? 0.5% or 0.05% citric acid solution? Ferrous sulfate. But because citric acid is acidic, it must be separated from nitrogen fertilizer spraying. Eight days.
Sixth, manganese deficiency
Manganese can participate in photosynthesis. When maize is moderately deficient in manganese, the leaves will appear less obvious stripes and the color of the leaves will become lighter. When maize is seriously deficient in manganese, the leaves will have a long white striped temperature, the center will turn brown, and then die.
Used to prevent and control manganese deficiency in corn, spraying 0.05? 0. 1% manganese sulfate, good benefit.
Seven. Boron deficiency
Boron can promote the normal development of reproductive organs and make corn grains full. Boron deficiency is first manifested in the most tender leaves, and there are irregular white spots between veins, which affect flower bud differentiation and lead to stem cracking.
The prevention and treatment of corn boron deficiency can be started by spraying boric acid or borax when the disease is found at seedling stage, and the concentration of boric acid is 0.025? 0. 1%, borax concentration is 0.05? 0.2%。
Eight, zinc deficiency
Zinc can promote the synthesis of auxin, which is called "zinc" force. Zinc-deficient maize plants usually show symptoms within two weeks after the seedlings are unearthed, with light stripes on the leaves, and then a broadband white flower tissue appears on both sides of the midvein, while the midvein and edge are still green.
Used to prevent zinc deficiency in corn, it can be used from seedling stage to jointing stage. If albinism is serious, the dosage is 0.5? 1% urea solution? Spraying zinc sulfate or dipotassium zinc sulfate twice every 10 day can solve the problem.
Lack of molybdenum and copper
When maize lacks molybdenum, its young leaves wither and its edges die. When copper is deficient, the young leaves turn yellow and lose their green symptoms, and finally the leaves dry and fall off.
0.0 1% ammonium molybdate and 0.0 1? 0.5% copper sulfate has a remarkable effect.
In short, when there are different element deficiencies in corn, different fertilizers should be sprayed in time to avoid reducing production. But after all, foliar spraying can only remedy it. In order to fundamentally solve the problem of soil nutrient deficiency, a variety of fertilizers should be mixed. Manure and crop straw are good trace element fertilizers, so more manure should be applied before sowing corn. If the amount of zinc, boron and manganese base fertilizers per mu is 1 kg, 0.5 kg and 1.5 kg, respectively, the problem can be solved. The plot with normal corn growth and development, 0.2? 0.3% potassium dihydrogen phosphate 2? Three times, the corn yield can be increased by more than 10%, 0. 1? 0.3% zinc sulfate solution can prevent albino seedlings of corn. When spraying foliar fertilizer, brassinolide and other substances can be added appropriately, and the yield increase effect is obvious.