This article comes from the WeChat public account: Earth Knowledge Bureau (ID: diqiuzhishiju) , author: Tim is the one, from the title figure: vision China
Recently, Heilongjiang ’s open burning of straw has caused heavy air pollution in Northeast China , which has aroused widespread concern among locals.
The red warning indicates that the air quality index in the area has been above 500 for 24 consecutive hours (picture from: Harbin Meteorology / weibo)
Every day is bathed in the gray air, and indeed no one can stand it, and whoever encounters it is unlucky.
In fact, it’s not just the Northeast. Every season, it’s time to burn straw in the open air. Farmers stole the fire at night, and the patrol went to the house during the dayCha has become a cat-and-mouse game with repeated bans. And the citizens living in the city, who do n’t know what happened, only to see a black air floating above their heads …
Straw is not straw?
The term “straw” is a high-frequency vocabulary in the field of environmental protection. Speaking of farming, Village pollution always can’t get around this kind of substance that emits thick smoke when it burns . But few people actually know how big the “straw” family is and how difficult it is to manage.
Taking the word “straw” for example, most people have no idea about the word “straw”, and most of them fall on the word “straw”. Mistakenly think that straw is a variety of stalks , That is, the rod-shaped waste left after the crops are harvested. The most common thing I usually see is the stalk represented by corn.
However, corn stalks are only a small category of straw, and they do not even represent corn stalks. In fact, the concept of straw is very complicated. It is the general term for stem leaves, vines, or ears of the remaining aerial parts of the crops after harvesting their mature seeds. Therefore, the wastes such as leaves and cobs after peeling corn are regarded as corn stalks.
Naturally, straw is not limited to corn waste. At present, the crops in China are classified according to usage and botany system and can be divided into three major crops and eight major categories , respectively: food crops, including cereal crops and legume crops; economic crops, including fiber crops , Oil crops, sugar crops, etc .; green manure and feed crops.
Among them, because the green manure and feed crops can be harvested and used, the utilization rate is 100%, and no waste is generated, so they are not included in the category of straw. So the scope of straw is just under the two major crops of food and economy , but as many as more than 20 kinds of ground wastes including rice, wheat, potato, sorghum, sugarcane and other crops belong to straw.
It can be said that as long as there are places where crops are produced, such as the North China Plain, the Northeast Plain, and the middle and lower reaches of the Yangtze River in several major grain-producing regions of China, straw will be produced.
The properly used straw is a resource, and the total amount in China is relatively abundant. However, due to factors such as geography, climatic environment and planting system, its distribution is also regionally different . Generally speaking, crop straw productionThe grain output is positively correlated, so the areas with high grain output are also relatively rich in straw resources.
The approximate area of land used for planting in China
You can see the clues from the total straw resource data in 2014, and there are only 3 provinces (于 黑 鲁) span> The straw output exceeds 50 million tons, which is actually the main body of the North China Plain and the Northeast Plain; as many as 13 provinces with 20 million to 50 million tons; 6 provinces with 10 million to 20 million tons There are also 9 provinces below 10 million tons, accounting for nearly one-third of the first-level administrative regions in mainland China, including Beijing, Tianjin, Shanghai, Nanjing and Tibet.
What are the consequences of burning straw?
With such a large number of straws, if not handled properly, it will have a series of undesirable consequences. Incineration is the most unscientific type of treatment. Although it can achieve the effect of adding fertilizer to the land and saving space, the negative effects are also endless.
The first is to pollute the air environment. Due to the burning of straw by villagers around the urban area, the ambient air quality of the city is seriously reduced The content of the substance has increased significantly, especially the night air pollution has increased, and people in the relevant areas must have a deep experience. Once in the “season burning season”, a strange smell will always be smelled at night, which is “suffocating” .
Going further, according to the data released by the official environmental testing departments in various regions, when straws are burned, the sulfur dioxide, nitrogen dioxide, and respirable particulate matter in the atmosphere The three pollution indexes can usually reach high peaks , Several times more than usual.
When the concentration of respirable particulates in the air reaches a certain level, it will cause people to cough, chest tightness, and tears. In severe cases, it may cause multiple complications such as bronchitis , “suffocating “That’s how it came from.
Furthermore, the risk of fire is also a problem that has to be paid attention to. China has a large cultivated area. Due to the relatively open field, when the straw is burned, the air convection accelerates, and the wind speed increases, changing the wind direction from time to time. There will also be a “fire mass” floating in the air , which is difficult to control artificially , Easy to rush to the courtyard and fields.
The fires of houses, crops and forests caused by burning straw in recent years are endless. This will not only cause losses to crops and property, but also cause death and injury to humans and animals in severe cases . The front-line firefighters are undisturbed. Every year when the straw season comes, it is necessary to publicize the ban on burning straw, but with little success.
The billowing smoke produced during the burning of straw is also a big problem. When convection is slow, it will directly affect the normal operation of civil aviation, railways, and highways , posing a potential threat to traffic safety. In the sparsely populated Northeast China, roads, railways, and airports often have large amounts of farmland. These smogs will cause reduced air visibility and reduced visibility, which may affect the normal operation of traffic. May cause traffic accidents.
Additionally, even the addition of fertilizer, one of the good results of burning straw, can have side effects. When the straw is burned in the farmland, the surface temperature of the farmland will rise sharply, and some beneficial microorganisms in the soil will be directly burned to death, but the underground pests will accelerate the hatching, affecting the microcirculation of the farmland biosphere . The grass ash left over from incineration has the effect of transporting potassium fertilizer, but because it is alkaline, it will increase the soil alkalinity and greatly reduce the natural fertility and water retention performance.
After soil moisture loss is 65% ~ 80%, consolidation is not drought-tolerant , which affects the full absorption of soil nutrients by crops and directly affects the yield and quality of crops.
Actually, farmers have always believed that fertilization of grass and ash is a pre-modern backward option . During the incineration process, the organic matter and nitrogen nutrients in the straw will be lost, leaving only some potassium and mostly insoluble phosphorus, that is, the nutrients will be converted into gaseous state and only inorganic salts will be left, which is difficult to be absorbed by crops.
Using straw? Difficult!
In fact, people who are engaged in agriculture are not ignorant of this, and they even have some research achievements. After all, they are the frontline of agriculture.
Such as mechanized straw return to the field, straw biodegradation return to the field, straw cultivation of edible fungus, straw breeding livestock to return to the field, straw gasification, biological power generation, ethanol production, etc., Development of these industrial raw materials using straw Various forms of comprehensive utilization of technology and high-tech engineering Daoli are estimated that farmers have listened to it hundreds of times, but the actual implementation is still few.
First is the transformation of rural energy structure . Today, cooking with electricity and gas is convenient and hygienic, so straw is rarely used as fuel for cooking. The commodity value of straw is also low, few people buy it, and recycling is not profitable.
In terms of technology, the straw returning to the field must be mixed with the soil of the tillage layer or buried under the topsoil, otherwise it cannot be sown at all. Most of them are planted by direct seeding of rice, and the land must be flat and not leaking. Straw cannot be flattened on the ground , and when it is time to grab the farm, you cannot wait for the straw to rot before planting. Even if the seedlings are planted, it must be ensured that there is no large amount of straw residue in the shallow surface layer of the soil.
Operation is so troublesome, which has resulted in many farmers not mastering the method of returning straw to the field. The time and amount of returning the field are not yet clear. The effect of the operation is not only not obvious, but straw is easy to appear. The phenomenon that microorganisms and crops compete for nutrients during the rot process.
The quantity of agricultural machinery is difficult to meet the needs of straw treatment is also a big reasonBecause, especially the mechanical gap between the baler and the straw returning field is large . In addition, as straw returning to the field requires a variety of procedures and corresponding mechanical supporting operations, operation costs have also increased . The large increase in the cost of returning machinery to fields has objectively affected farmers’ enthusiasm for applying machinery to return straw to the fields.
In addition to the fact that most of the young and middle-aged people in rural areas now go out to work, the rural labor force is lacking. The time for harvesting and sowing is tight, and the time and labor for returning fields is not economically feasible.
Although there are so many objective disadvantages, people are still exploring and promoting the use of straw .
In addition to some early “ancient methods” of straw utilization technology, new straw utilization technology has gradually appeared in the public’s field of vision.
Green straw building materials have been used in many countries for nearly 30 years. In some countries, the utilization rate of straw building materials is as high as 80%. Recognized as high-tech green environmental protection building materials in the new century by various countries Materials are promising in China, where large-scale construction is underway today.
Stalk honeycomb coal can also replace coal and gas as high-quality fuel for civil and industrial applications. They can be used for domestic heating. It is indispensable in the usual barbecue and stew cooking.
The technology of straw microbial additive fermented feed can be used for breeding earthworms, insects, etc., and they can also be used as feed for farming chickens, ducks, fish and shrimps, and the excrement of animals such as chickens and ducks can be used to return to the field. Forming a closed-loop ecological circular economy technology is far better than burning it directly.
Technology has gradually matured, and perhaps all we need is the patience to change our concepts.
Reference:
Xu Shuli. Current status and utilization of straw resources in China [J]. Animal Husbandry and Feed Science (11).
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