The Beginning of Autumn should pay more attention to the extra-root topdressing of cotton.

Extra-root topdressing of cotton is commonly known as foliar spraying, that is, spraying fertilizer solution on the stems and leaves of cotton plants to make the stems and leaves absorb nutrients and achieve the purpose of nourishing the whole plant (including root system). It has the advantages of saving fertilizer, quick effect and not restricted by soil conditions. it is an important yield-increasing measure to replenish nutrients to cotton plants in the later growth stage, especially after "the Beginning of Autumn". Why do you say so?

Many studies have proved that the nutrients absorbed by leaves can be transported and assimilated in vivo as those absorbed by roots, and extra-root topdressing is a way for plants to obtain nutrients, so foliar fertilizer spraying in the later stage can also slow down root senescence. Further studies show that there are many fine structures on the outer wall of the foliar epidermal cells, such as the pore cells, the base and periphery of the leaf hairs and the upper and lower epidermal cells of the leaf veins. these fiber pores connect the cell protoplast directly with the outside world, which is a channel for nutrients to enter the cell protoplast, and it is an active absorption process.

After "the Beginning of Autumn" solar terms, cotton has entered the late stage of flower and boll, and the ability of root system to absorb nutrients is weakening day by day, while the upper cotton buds are still growing and developing continuously, in fertilizer-deficient cotton fields with little fertilization, or in cotton fields with more bolls in the middle and lower parts and malnutrition in the upper parts, it is an important period for foliar fertilizer spraying. In the cotton fields without potash fertilizer or Rain Water in the early stage, obvious symptoms of potassium deficiency have appeared in the lower old leaves at present. With the increase of bolls and rainfall, potassium deficiency will be further aggravated. If available potassium is not replenished in time, it will cause premature senility, less bolls, poor boll opening, decreased lint percentage, and even cotton plant death. Therefore, foliar potassium spraying is a necessary yield-increasing technique in most cotton fields in the later stage.

First, spraying potash fertilizer varieties, high-quality potassium sulfate is the most suitable for high-quality potassium sulfate, also known as first-grade potassium sulfate, which contains more than 50% potassium oxide (K2O). The dosage form should choose powder or microcrystal which is soluble in water. No other foliar fertilizer containing potassium can reach the potassium content of potassium sulfate. Therefore, potassium sulfate is the most affordable and safest variety of foliar fertilizer spraying. For example, Russian-made "Epp" potassium sulfate contains up to 52% K2O and is easily soluble in water (13 grams of potassium sulfate per 100g of water at 30 ℃). According to the calculation of spraying 3 times per mu, 0.6kg / mu of fertilizer per mu and 70% utilization rate, K2O0.66 kg / mu can be absorbed and utilized, and these potassium can meet the needs of increasing seed cotton by 15 kg per mu.

Second, cotton leaves should be sprayed wet on both sides when spraying fertilizer. From the leaf structure, there is spongy tissue under the epidermis on the back of the leaf, which is relatively loose, the cell gap is larger, and there are more pore cells, while the palisade tissue of the front epidermis of the leaf is denser and absorbs less nutrients than the back of the leaf. And slow, so spray should strive for both sides of the leaf to be fully covered with solution. Do not spray less than 30 kg per mu, of which 0.6 kg of potassium sulfate (2% concentration) is mainly sprayed on both sides of the leaves of the upper half of the cotton plant.

Third, in the windless weather in the evening, it is best to spray fertilizer solution to wet leaves for a long time, the better the fertilizer effect. It is generally required that the wet time can be maintained for 0.5 hours, so it is best to spray it in windless or cloudy days in the evening.