From "the emperor who sells dung" to "the place where grains are reincarnated", why do we apply fertilizer?

For most of the long time, agriculture, especially food production, has been the absolute priority in human society: if enough food cannot be produced, famine will occur, which will lead to population shrinkage and social unrest, posing a great threat to the continuation of civilization. In order to ensure food production, in addition to expanding the total area of ​​cultivation (that is, reclaiming land for farming), efforts to increase food production per unit area have become an important task that cannot be ignored in every period.

Why fertilize?

The two most common and important measures to increase the unit yield of grain are fertilization and irrigation. We all know that chemical reactions follow the "law of conservation of mass", and a seed, from seedling to flowering and heading, and finally producing a large amount of rice, must also follow this law: the various elements contained in rice cannot be produced out of thin air, but can only be obtained from air, water and soil. To be precise, they are obtained from organic matter (mainly humus) in the soil.

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Of course, the humus in the soil is limited. When it is exhausted, the land will become barren. There are two solutions: implement crop rotation to give the land a rest; and apply fertilizer properly to replenish the nutrients absorbed by the plants. This is the fundamental reason for fertilization.

The evolution of fertilizers

Ancient

It is very likely that the value of fertilization was discovered in several ancient civilizations. Unearthed artifacts show that in the Huxiu culture about 4,000 years ago, there was a practice of "using mud as fertilizer" (scooping up silt from rivers and lakes, transporting it back in small boats, and then using it as fertilizer). Later, it should be a very common practice to use human and animal feces as fertilizer. The ancient toilet was jokingly called "the place where grains are reincarnated", which comes from this. During the reign of Emperor Taizong of Tang, there was also a joke about "the emperor selling feces", which is enough to prove that the understanding of fertilizer at that time was already very profound.

Modern times

The disadvantages of manure are obvious: limited production, odor that attracts flies, bacteria, parasite eggs, viruses and other pathogenic microorganisms in manure that breed and spread in the land and irrigation water, and may cause various human and animal diseases. Therefore, in modern times, my country's agriculture generally composts manure first, that is, piles it tightly together, uses microorganisms to ferment and decompose it, and generates high temperatures to kill pathogenic microorganisms. A more reliable way is to put them into a biogas digester to produce biogas, and then use the waste residue as fertilizer.

Later, with the support of the chemical industry, humans gradually found a substitute for manure: chemical fertilizers (referred to as fertilizers). As artificially synthesized inorganic compounds, fertilizers can be used separately for nitrogen, phosphorus, and potassium fertilizers, or they can be mixed in advance (called "compound fertilizers"), so that only one application is needed to meet the needs.

After World War I, in order to solve the shortage of raw materials for ammonium nitrate explosives, German Fritz Haber invented a practical method of synthesizing ammonia in 1909, which indirectly promoted the explosive production of fertilizers.

In 1978, my country established the Chitianhua Company, then the largest company in the country, in Chishui, marking a solid step towards self-sufficiency in fertilizers.

What does the future hold?

The extensive use of chemical fertilizers has also brought many problems: its nutrient composition is relatively single, and if only one type of chemical fertilizer is used for a long time, it is easy to cause the nutrient composition of the soil to be unbalanced, or even the soil to become compacted; when irrigation water flows through the fields, it will carry away some of the chemical fertilizers, which can easily lead to eutrophication of the water body and cause serious environmental pollution. At the same time, you still have to pay for the purchase of chemical fertilizers, which also raises the cost of growing crops and affects farmers' income.

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In recent years, countries have begun to pay attention to the negative impact of excessive use of fertilizers on the ecological environment. In 2015, my country's Ministry of Agriculture issued the "Action Plan for Zero Growth in Fertilizer Use by 2020", which proposed the idea of ​​reducing the use of pesticides and fertilizers. Specifically, it is to reduce the use of pesticides and fertilizers while ensuring that grain production does not decrease.

To achieve this, the key is precise fertilization: agricultural technicians first analyze and test the soil of a specific plot of land to find out its demand for nitrogen, phosphorus and potassium, and then apply fertilizers in a targeted manner to ensure that "what is lacking is replenished".

Secondly, we should vigorously promote the use of green manure. No matter what kind of food crop, only part of it can be eaten, and the rest cannot be eaten, such as the stems, leaves, vines, and straw of the plant. However, these things also contain rich organic matter. If they are thrown away or burned as waste, it is really a waste. Therefore, after simply processing them (such as crushing, composting), burying them in the soil, or covering them on the soil, they can be used as fertilizers to return some nutrients to the soil.

Another application is the application of slow-release fertilizers. This type of fertilizer is like a small dumpling, with a waterproof film completely wrapping the compound fertilizer inside, so that the fertilizer will not be released into the soil all at once; and there are tiny holes on the film, which can slowly dissolve and release the fertilizer under the action of moisture and pressure in the soil. There are also some slow-release fertilizers that use organic polymers such as urea formaldehyde, which are insoluble in water, but can slowly decompose in the soil, while releasing ammonia salts for plants to use, achieving the effect of "one-time fertilization, long-term effect".

By the end of 2020, the Action Plan for Zero Growth in Fertilizer Use by 2020 had been successfully completed.

Of course, to achieve the dual goals of increasing agricultural production and protecting the environment, we must fundamentally adhere to the guiding ideology of "both mountains of gold and silver and green mountains and clear waters", not over-demand from nature, and promote the harmonious development of man and the environment.

Source: Chongqing Science Writers Association

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