When the cotton plant lacks potassium, the potassium will be transferred from the old leaves to the young tissues. Therefore, the potassium deficiency in the cotton will be the first to appear in the lower old leaves, the veins will remain green, and the leaves will fade gradually. In particular, in the middle and early September, in the condition of continuous low-temperature and autumn rain, potassium-deficient cotton fields will effectively interrupt the supply of available potassium in the soil, and the cotton plant will suddenly fail. The cotton leaves will turn yellow or red quickly in 2-3 days, and then dry and fall off. The culm was dead and the cotton plant died (this symptom is also called "red stem blight"). If the potassium is not replenished beforehand, it will result in the reduction of bells on the upper part of the cotton plant or the absence of bolls, delayed bolls, poor bolling, reduced lint, leaf shedding, and even the death of the whole plant.
Therefore, the post-autumn period (usually in the middle and early August) is the critical period for applying potassium fertilizer to cotton. Potassium application after the autumn of cotton is usually carried out by applying fertilizers outside the roots. There are mainly the following methods.
Spray potassium sulfate. The potassium oxide in potassium sulfate is as high as 52%, and it dissolves quickly, with almost no precipitation. It is the first choice for potassium. In general, 0.5 kg of potassium sulfate is used to spray 100 kg of water per mu, sprayed once every 7 days, and sprayed twice.
Spray potassium chloride. Potassium oxide in potassium chloride up to 60%, but also more easily soluble, but the cotton leaf is more sensitive to chloride ions, such as foliar spray fertilizer, generally suitable concentration of 1%, that is, 1 kg of potassium chloride per acre of water 100 kg spray, spray once every 7 days, even spray 2 times.
Spray 1% of grass ash leaching solution. Plant ash is rich in potassium, commonly used as foliar fertilizer, generally per acre with 2 kg of plant ash to 100 kg of water filtration leachate spray, spray once every 5 days, and even spray 2 or 3 times.
Spray potassium dihydrogen phosphate. In general, 0.2 kg of potassium dihydrogen phosphate per acre is sprayed on 100 kg of water, sprayed once every 7 days, and sprayed twice. However, it should be noted that potassium dihydrogen phosphate is only suitable for use in cotton fields where vegetative growth is prosperous and has late maturation, premature aging, early maturing cotton fields, and cotton fields with prosperous reproductive growth and weak vegetative growth can no longer be sprayed with potassium dihydrogen phosphate. .