Fertilizer acid and alkaline knowledge Daquan
Many farmers buy chemical fertilizers and apply chemical fertilizers. They basically do not consider the acidity and alkalinity of cultivated soil, and do not consider the acidity and alkalinity of chemical fertilizers. They only consider the nutrient content of chemical fertilizers and the ratio of N, P, K, which results in poor fertilization. In fact, mastering the acidity and alkalinity of fertilizers is very helpful for rational fertilization.
Acid-base reaction characteristics of fertilizers
Commonly used fertilizers are salts composed of bases and acid radicals and basically have chemically specific properties. On the other hand, after fertilization, it is influenced by soil environmental factors such as selective absorption of nutrients by root groups and microorganisms, decomposition and transformation of microbial secretases, molecular adsorption of cations and anions of soil particles, and desalination of water by rain. And so on, will have a clear influence on the vegetative growth of plants and changes in soil chemistry.
Fertilizers in chemical acid-base reactions
After the fertilizer is dissolved in the water, due to the relative strength of the base and the acid radical, the pH of the aqueous solution of the fertilizer has the difference of acidic or alkaline reaction. According to the level of pH, the fertilizer can be divided into acidic fertilizers, neutral fertilizers and alkaline fertilizers. The strength and weakness of bases and acid radicals from the composition of the fertilizer can also be used to judge whether the chemical properties of fertilizers are neutral, acidic or alkaline. For example, ammonium sulfate is composed of strong acid and weak base, so its aqueous solution is slightly acidic; potassium sulfate is composed of strong acid and strong base, so its aqueous solution is neutral; potassium carbonate is composed of weak acid and strong base, so its aqueous solution is microscopic. Alkaline. Some fertilizers have residual free acid in the manufacturing process. For example, superphosphate often contains free sulfuric acid, and its aqueous solution is also slightly acidic. The chemical-acid-base reactions of fertilizers are summarized in Table 1.
Fertilizer has the characteristics of chemical acid-base reaction, so pay attention to the mixture of acid and alkali will have a fever, alkali and alkali will cause deamination and other situations.
Physiological acid-base reaction of fertilizers in plants
After the fertilizer is applied to the soil, the acid-base reaction in the soil solution is slightly different from the acid-base reaction of the simple fertilizer solution. The chemical acid-base reaction of fertilizers is affected by the buffering ability of soil colloidal particles, and the effect on the acid-base changes of soil solution in a short period of time is not very large. Instead, the absorption of fertilizer salt ions by plant roots is not balanced. Afterwards, the pH of the soil solution changed more significantly.
In general, after the cations in the fertilizer component are absorbed by the root system, residual nitrate (NO3-), chloride (Cl-), sulfate (SO42-), etc. are loaded with the same load as the soil colloid, making it easy. With the soil gravity water is discharged out of the soil, but at the same time, the base cations such as calcium ion (Ca2+), magnesium ion (Mg2+), and potassium ion (K+) adsorbed by the soil will also be dragged along with the loss. To the soil acidification.
In addition, ammonium nitrogen fertilizers, such as ammonium sulfate, are applied to the soil. The ammonium nitrogen is absorbed by the plant and the rest is converted to nitric acid by the action of nitrifying bacteria. From then on, the process in the soil is like Normal nitrate fertilizers also cause soil acidification.
The acidity of the fertilizer is lost in the soil with the water, resulting in the loss of bases and the severity of the acidification of the soil, with hydrochloric acid and sulfate as 1 and nitrate as 1/2 and phosphate as 1/3. According to the above, after the fertilizer is applied, according to the change of the acidity and alkalinity of the soil, it can be classified into the physiological acidic fertilizer, physiological neutral fertilizer and physiological alkaline fertilizer of Table 2.
Note 1. When calcium superphosphate is applied to acidic soils, it has little effect on pH, but in alkaline soils, due to the presence of paraglycidants, it behaves like a physiological acid fertilizer.
Note 2. The performance of urea in dry fields is an acidic fertilizer, the main reason being due to nitrification. The performance of urea in paddy fields is due to the dilution of the base water and the amount of water brought in by irrigation water, so the response to soil acid and alkali is attributed to the neutral fertilizer.
Nitrogen fertilizer and potash fertilizer are two kinds of fertilizers that require the largest amount of fertilizers and the three most important fertilizers. In particular, ammonium sulfate, ammonium chloride, and potassium chloride are all physiological acid fertilizers. These fertilizers are used to cause soil acidification in successive years. main reason.
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