What potassium fertilizer products are there? Master application methods and the timing of potassium supplementation
Some farmer friends, when it comes time to supplement potassium fertilizer, still do not understand the importance of potassium fertilizer, what potassium fertilizer products there are, and how they should be applied, causing them to miss the timing for potassium supplementation. Potassium is one of the three essential fertilizer elements. Potassium in plants generally accounts for 0.2%-4.1% of dry matter weight, second only to nitrogen. During plant growth and development, potassium participates in all kinds of life activities of plants, and can also enhance crop stress resistance and improve crop quality. In short, potassium occupies an important position in agricultural production.
1. Types of potassium fertilizer
Potassium-bearing minerals, especially soluble potassium mineral salts, are the main raw materials for producing potassium fertilizer. Potassium fertilizer can also be extracted from salt lake water, salt well water and brine.
(1) On the naming of potassium fertilizer
Potassium fertilizer belongs to a strong-base salt of a certain acid. Its naming depends on the corresponding acid radical: the one corresponding to nitrate radical is called potassium nitrate, the one corresponding to sulfate radical is called potassium sulfate, the one corresponding to hydrochloride radical (also called hydrochloric acid) is called potassium chloride, the one corresponding to carbonate radical is called potassium carbonate, the one corresponding to phosphate radical is called potassium phosphate (monopotassium phosphate, dipotassium phosphate, tripotassium phosphate, potassium polyphosphate, potassium polymetaphosphate, etc.), the one corresponding to organic acid radicals is called organic potassium (potassium formate, potassium acetate, potassium citrate, etc.), and the one corresponding to silicate radical is called potassium silicate……
(2) Main products
Plant ash——mainly contains potassium, phosphorus, calcium, magnesium, sulfur, silicon and various trace elements, but is dominated by potassium and calcium. It is a quick-acting alkaline potassium fertilizer. During storage, avoid rain and soaking in water. It should not be mixed and used at the same time with ammonium nitrogen fertilizer, water-soluble phosphate fertilizer and fully decomposed organic fertilizer (such as human and livestock urine). It is rich in calcium and cannot be stored or mixed with superphosphate. It is suitable for various soils except saline-alkali soil, especially suitable for acidic soil. Plant ash can be used as base fertilizer, topdressing and seed-covering fertilizer, and can also be used for foliar topdressing. The dosage is 50-100kg/mu, and a small amount of water should be added to moisten it before application. When used as base fertilizer, it should be applied in a concentrated way, by furrow application or hole application, and covered with soil after application. When used as topdressing, it can be sprayed on the leaves. When used as seed-covering fertilizer, it is used as a covering material for vegetable seedbeds. Using a 1% plant ash water extract as foliar topdressing can also control aphids.
Potassium chloride——potassium content 60%, commercial fertilizer content 50%-60%, suitable for various soils except saline-alkali soil. On acidic soil or soil where potassium chloride has been applied heavily for a long time, attention should be paid to the combined application of organic fertilizer, calcium magnesium phosphate fertilizer, phosphate rock powder or other alkaline fertilizers. On neutral soil, when potassium chloride is applied for a long time, calcium fertilizer should be applied together. On melon and fruit vegetables and under protected cultivation conditions, potassium chloride should be applied reasonably or in small amounts according to crop and soil conditions. It is strictly forbidden to apply double-chloride fertilizer made from potassium chloride and ammonium chloride. In dry seasons, the amount of potassium applied to the soil needs to be appropriately increased. It can be used as base fertilizer and topdressing, but not as seed fertilizer. When used as base fertilizer on neutral and acidic soils, it should be used together with organic fertilizer, phosphate rock powder, etc. When used as topdressing, it should be applied earlier, and the application rate is generally 5-15kg/mu. The application rate as base fertilizer can be slightly more than that as topdressing. Chlorine-sensitive crops such as potatoes should not be treated with it; potassium fertilizers that do not contain chloride ions, such as potassium sulfate, can be used. The advantages are low price, high potassium content, good quick solubility, and it is a neutral fertilizer. The disadvantages are that dissolution absorbs heat, it easily absorbs moisture, contains chlorine, and long-term heavy application has certain side effects.
Potassium sulfate——contains 48%-52% potassium and 18% sulfur, light gray or slightly yellow, easily soluble in water, is a high-concentration quick-acting potassium fertilizer, suitable for various crops and soils, especially suitable for chlorine-avoiding and sulfur-loving crops, such as tuber crops, onions and garlic, etc. On acidic soil or when applied for a long time, it should be applied together with calcium magnesium phosphate fertilizer, phosphate rock powder or other alkaline fertilizers to prevent soil acidification and compaction. When applied on sulfur-deficient soil and on vegetables with a relatively high sulfur requirement such as onions, Chinese chives and garlic, the effect is good, so it should first be used on chlorine-sensitive and potassium-loving and sulfur-loving crops. It should not be applied to aquatic vegetables. When applied on neutral and calcareous soil, it should be combined with organic fertilizer. For sandy soil with poor water and fertilizer retention capacity, base fertilizer and topdressing should be combined and applied separately. It can be used as base fertilizer, topdressing, seed fertilizer and foliar fertilizer. When used as topdressing, it should be applied early. When used as base fertilizer and topdressing, concentrated fertilization methods such as band application, furrow application and hole application should be adopted, with an application rate of 7.5-15kg/mu. The application rate as seed fertilizer is 1.5-2.5kg/mu. The concentration for foliar fertilization is 2%-3%. The advantages are relatively low price, high potassium content, not easy to absorb moisture, and it can provide sulfur. The disadvantages are that dissolution absorbs heat, it is weakly acidic itself, belongs to physiologically acidic fertilizer, and the sulfur it contains easily combines with calcium to form slightly soluble calcium sulfate, which can cause soil acidification and compaction after application.
Potassium dihydrogen phosphate——contains 52% phosphorus and about 34% potassium. It is a chemically neutral and physiologically neutral fertilizer with good water solubility. Generally, before and after flowering, it can be used to promote root germination and flower bud differentiation, providing energy for flowering and fruit setting; use during the coloring stage can promote powder formation and coloring and increase fruit sweetness; use after fruit harvest can promote branch maturity and increase the degree of fruit lignification. It can be used for seed soaking, seed dressing, root dipping, root irrigation, foliar spraying and root application. Using it at key crop growth stages is both economical and more effective. For example, seed soaking and seed dressing before sowing; the jointing stage, booting stage and heading stage of grain crops; and the seedling stage and full flowering stage of cotton, rapeseed, peanut, vegetables and tuber crops give the best results. The advantages are that it is not easy to absorb moisture and has a high total phosphorus and potassium content, and it is currently an essential raw material in high-content powder water-soluble fertilizers. It supplements phosphorus and potassium elements at the same time, with a small dosage and obvious effect. If its disadvantages must be mentioned, it is that there are somewhat many counterfeit products, so when purchasing, please look for regular manufacturers
Potassium nitrate——contains 13.5% nitrate nitrogen and 46% potassium; it is a chemically neutral and physiologically neutral fertilizer with good water solubility. Long-term application will not cause soil acidification. It is suitable for the young fruit expansion stage to the early coloring stage of fruit trees, and can promote the expansion of fruit flesh cells. Because it contains nitrate nitrogen, it is not recommended for use in the late coloring stage, as it easily causes regreening. It moves easily in the soil, making it suitable for crop topdressing, especially for topdressing at the middle and late stages. The advantages are moderate price, good quick solubility, not easy to absorb moisture, neutral fertilizer, and the nitrate nitrogen it provides is absorbed quickly. The disadvantages are that dissolution absorbs heat and lowers soil temperature, under adverse conditions it easily causes the accumulation of nitrite in crops (prohibited in organic agriculture), and it belongs to nitrate, which has certain safety hazards during storage and processing.
2. Effective application of potassium fertilizer
The effective application technology of potassium fertilizer is affected by many factors, among which soil type, fertility level, crop type, fertilization method and other factors have a relatively large influence.
(1) Applying potassium according to soil
The degree of soil potassium deficiency is the prerequisite for effective potassium fertilizer application. First, the effect of soil available potassium content on potassium fertilizer efficiency should be considered. The size of potassium fertilizer efficiency is closely related to whether soil available potassium is abundant or deficient, that is, under otherwise identical conditions, the lower the soil available potassium content, the better the fertilizer efficiency of potassium fertilizer in the current season.
Soil with available potassium content less than 40 mg/kg is soil extremely deficient in potassium, and potassium has become a limiting factor for crop yield increase, so it should be applied first, with a rate of 5-10 kg per mu, equivalent to 10-20 kg of potassium chloride or potassium sulfate. No matter what soil and crop, the yield increase effect is very significant. When soil available potassium content is 40-80 mg/kg, it is potassium-deficient soil, and the potassium fertilizer rate per mu is about 5 kg, and the yield increase effect is also very significant. When soil available potassium content is greater than 80 mg/kg, except for some potassium-loving cash crops, grain crops can be given less or no potassium. At the same time, soil slowly available potassium content, soil texture and degree of maturation, etc. should also be considered.
Soil slowly available potassium cannot be directly absorbed and used by crops. It is the source and reserve of soil available potassium. When soil available potassium content is similar, the lower the soil slowly available potassium content, the slower the speed of conversion into available potassium. The fertilizer efficiency of applying potassium fertilizer is often better. However, as a guide for potassium application in the current season, soil available potassium content is the main basis.
In coarse-textured sandy soil, because the potassium level is low and the available potassium in the soil is also easily lost through leaching, the effect of potassium application on this type of soil is often better than on clayey soil. The fertilizer efficiency of adding potassium fertilizer to highly matured soil is generally not as good as that on soil with a low degree of maturation. This is because the former is relatively rich in potassium and has good soil physical and chemical properties, with strong potassium supply capacity. Soils in southern China have low potassium content, so the focus of potassium fertilizer application should be in the south; however, the area of potassium-deficient soil in the north is gradually expanding, especially in some high-yield soils, where potassium deficiency is becoming increasingly serious.
(2) Applying potassium according to crop
When the soil potassium deficiency situation is the same, potassium fertilizer should be applied first to potassium-loving crops. The order of potassium-loving crops is legume crops > tuber crops, sugar beet, sugarcane, watermelon, fruit trees > cotton, bast fiber crops, tobacco > corn > rice, wheat. Potassium-loving crops are relative. On severely potassium-deficient soil, no matter what crop is planted, the yield increase effect of potassium application is significant. On soil rich in potassium, adding potassium fertilizer to potassium-loving crops often does not increase yield.
Different varieties of the same crop also respond differently to potassium fertilizer. Taking rice as an example, hybrid rice and dwarf high-yield improved japonica rice have better fertilizer efficiency from added potassium fertilizer than tall-stalk varieties, indica rice and conventional rice.
For crops such as soybean, rapeseed, wheat, fruit trees and rice under harsh environments such as cold, drought and insufficient sunlight, adding or applying potassium fertilizer early can enhance cold resistance, reduce frost damage, and the yield increase effect is very good. For example, the black soil in Northeast China has relatively high soil available potassium and slowly available potassium content, but in recent years tests on soybean on black soil have shown that applying potassium fertilizer in cold and dry years has the effect of enhancing soybean cold resistance and drought resistance, and the fertilizer efficiency is also relatively obvious.
(3) Application rate of potassium fertilizer
The amount of potassium fertilizer also follows the law of diminishing returns. On potassium-deficient soil, crop yield increases with increasing potassium application, while the yield increase per kg of potassium fertilizer decreases with increasing dosage. When the dosage exceeds a certain range, yield cannot be further increased.
The suitable amount of potassium fertilizer should be determined by the level of soil available potassium, crop type and the mutual balance of various nutrient elements. Under the current situation of relatively scarce potassium fertilizer, it is generally still impossible to fully meet crop demand, so a potassium fertilizer rate of 3-6 kg per mu is appropriate. On potassium-deficient soil, generally each kg can increase rice yield by 5-10 kg. The current-season utilization rate of potassium fertilizer is 40%-50%. For potassium-loving crops on severely potassium-deficient soil, such as soybean, sweet potato, tobacco and sugarcane, the potassium fertilizer rate can be appropriately increased. For plots where soil potassium deficiency is not serious and the amount of farmyard manure is sufficient, potassium fertilizer can be applied less or not at all.
(4) Application period of potassium fertilizer
Potassium fertilizer can be used as base fertilizer, seed fertilizer or topdressing. Like phosphate fertilizer, potassium fertilizer has a better effect as base fertilizer or early topdressing, because the seedling stage of crops is often the critical period for potassium, and the response to potassium is very sensitive. Although potassium uptake by crops at the seedling stage is less than 1% of the whole growth period, the individual plants at the seedling stage are small and the relative amount is relatively large.
(5) Application methods of potassium fertilizer
Broadcast application followed by plowing into the soil with a plow; band fertilization with seeds or near the seeds at sowing; shallow cultivation after broadcast application (harrowing or paddy field harrowing); hole application; surface broadcast application; foliar spraying, etc.