The wider the color and gray bars, the higher the absorption efficiency of the nutrient; the thinner, the lower the absorption efficiency. The figure is the soil pH (pH).
Not long ago, the "Agricultural Resources Guide" published the article "Severe Acidification of Farmland Soils in China" by Professor Zhang Fusuo from the College of Resources and Environment, China Agricultural University. The article discusses that since the 1980s, China's farmland soil has experienced significant acidification, which has uncovered the severe facts that China's high-input and intensive agricultural production has accelerated the acidification of farmland soil in the past 20 years, which has aroused people's high attention.
Why is there good acidification in farmland? Which areas are currently acidified more seriously? What problems will soil acidification bring to agricultural production? How should agricultural workers deal with soil acidification? In response to the above problems, the author has found a large amount of information. Understand the status of soil acidification in the southern region.
The pH is generally lower than 5.5. The acidity of the southern soil is severe.
As we all know, from 2004 to 2015, China's grain production achieved "twelve consecutive increases" and created a miracle in the history of food in China and the world. As the “food†of food, fertilizer has made a major contribution to ensuring food security and agricultural production. However, in the long-term intensive production process, excessive use of chemical fertilizers and fertilization methods are unscientific, causing serious damage to the soil structure, leading to acidification and compaction of the soil.
According to incomplete statistics, as of 2015, China's acidic soil area reached 200 million hectares, accounting for 21% of the country's cultivated land area. The southern provinces represented by Guangdong, Guangxi, Hunan, Jiangxi, Fujian, Hainan, and Yunnan have serious soil acidification. “Red soil is the most important soil type in the south of the Yangtze River, and the pH value is below 5.5.†Xu Minggang of the Chinese Academy of Agricultural Sciences mentioned in the article “Red Soil Acidification and Integrated Control Technology in the Southern Region†that he found a lot of samples and found that Hunan Red Soil The pH value of dryland soil ranged from 4.5 to 6.1. Among them, acidic soil with pH≤5.5 accounted for 70.2% of the total sample; for 151 soil samples of citrus, litchi, longan and mango, the pH value of Guangxi was less than 4.5. Strong acid orchard, acidic orchard red soil with pH between 4.5 and 5.5, accounting for 34% and 49% of the total sample respectively; in addition, soil sampling pH values ​​in Guangdong, Fujian and Hainan are generally lower than 5.5, and acidification is very serious. .
Soil acidification caused by excessive fertilizer and unscientific
The root cause of soil acidification is: on the one hand, it is a natural factor. For example, strong precipitation will cause a large loss of alkaline salts such as potassium, calcium and magnesium in the soil, leading to acidification of the soil; on the other hand, human factors, the most important is long-term The application of acid fertilizers and nitrogen fertilizers, as well as the fertilization method, are unscientific, leading to acidification of the soil. Long-term use of physiological acid fertilizer for a long time, after the crop absorbs nutrients, the remaining acid roots combine with the hydrogen ions in the soil to form acid, which leads to soil compaction, enhanced acidity and destruction of soil structure. Taking potassium chloride and potassium sulfate commonly used in banana planting as an example, when potassium chloride is applied to the soil, potassium chloride is ionized into K+ and Cl-, and the banana absorbs the nutrient K+, so that the dissociation of potassium chloride proceeds to the right. The soil is enriched in a large amount of Cl-, and Cl- and H combine to form HCl, resulting in an increasingly higher degree of soil acidification.
The conversion of nitrogen fertilizer into the soil produces protons and is converted into nitrates. When nitrates are lost, they will take away alkaline ions such as calcium and magnesium. The large use of nitrogen fertilizer is also one of the important reasons for the increase of soil acidification.
Scientific fertilization
Soil acidification needs improvement
The pH of the soil solution affects the availability of soil nutrients, and the pH of the soil is critical for plant growth. Most nutrients have the highest or near highest efficacy at pH values ​​between 6.5 and 7.0, so most crops thrive in neutral or slightly acidic environments. When the soil is acidic or severely acidified, it will have a serious impact on crop growth.
Experiments have shown that soil acidification changes the micro-environment of the whole soil, resulting in an imbalance of micro-ecological environment for microbial survival, leading to soil diseases. Soil acidification also activates heavy metals in the soil. For example, when the pH of the soil drops by one unit, the activity of cadmium increases by 100 times. Therefore, the production of cadmium is not because the soil is completely contaminated, but because of the soil. Acidification greatly increases the activity of cadmium. In addition, soil acidification will also increase the loss of trace elements, resulting in imbalance of soil nutrients.
Professor Zhang Fusuo once experimented on crops such as wheat, corn, and legumes. The pH values ​​of the two adjacent plots were 6.1 and 4.2, respectively. The other conditions for wheat growth were the same. As a result, the yield of acidified fields was very low.
At present, the acidification situation of farmland in China is very serious. As the degree of intensive production of farmland increases and the demand for food increases further, the degree of acidification will increase. Therefore, it is urgent to improve soil acidity.
The author believes that in order to improve the trend of soil acidification, we must change the current production methods, starting from the following three aspects: First, we can not apply too much nitrogen fertilizer, can not only talk about high yield and then high yield, but also pay attention to weight loss and efficiency; Fertilizer, improve the soil through good fertilizer products, and gradually restore the acidic soil to a healthy state; third, improve agricultural production technology, use a small number of multiple fertilization methods or introduce integrated water and fertilizer technology to improve fertilizer utilization.
(Xi Yang)
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