Land is the foundation of human survival, but do you know the soil as an important part of the land? Leonardo da Vinci once sighed: “We know more about the motion of celestial bodies than we know about the soil under our feet.” Although this sentence is exaggerated, the soil is indeed very complex, and it is not so simple to understand it.
Earth, it’s not that simple
It is estimated that about 45% of the soil is minerals, the combined content of air and water is about 50%, and the rest is the remains or discharge of living things, as well as microorganisms such as fungi and bacteria. However, this ratio is only available in healthy soils. If the soil is specially affected, its composition may change. For example, in soils that are compacted by heavy equipment, air and water content can be greatly reduced. For another example, continuous high temperature and no rain will dry the soil and affect the survival of soil microorganisms.
We often hear the term “soil fertility”. Soil fertility refers to the ability of the soil to provide the nutrients needed for crop growth. Some people may think that “fertility” can be judged simply by the amount of nutrients in the soil, but this understanding is not entirely correct. NPK content, humidity, temperature, porosity, pH, salinity, toxic content, microbial species and activity… Fertility is a comprehensive reflection of these dazzling physical, chemical and biological properties.
Open the world map, the most fertile soil in the world – black soil is mainly distributed in four major regions, namely the Mississippi River Basin in the United States, the Great Plains of Ukraine and Russia, the Great Plains of Argentina and Uruguay, and Northeast China. Black soil is a clay soil with strong expansion, contraction and disturbance characteristics, which is very suitable for crop growth. Due to the existence of black soil, these regions are the main production areas of corn, soybean, rice, wheat and other crops in the world, and shoulder the heavy task of stabilizing the world’s food production.
precious black soil
peasants working on black soil
However, years of over-cultivation have led to the degradation of black soil in many places around the world, and the barren black soil is highly vulnerable to external influences and completely lost. In 1928, a huge storm swept through almost the entire Ukraine, and some places suffered damage to a 5-12 cm thick black soil layer, and it took 200 to 400 years to form a 1 cm thick black soil layer under natural conditions. In 1934, another storm hit the eastern United States and western Canada. Due to the exposed surface, the storm swept away 300 million cubic meters of surface black soil with high organic matter content, resulting in a decline in soil fertility and a reduction of 5.1 million tons of winter wheat in the United States that year. The loss of black soil is a serious threat to world food security, and countries have put the protection of black soil into the agenda. my country is taking various measures to strengthen the protection of black soil, “refueling” the black soil, consolidating the foundation for stable grain production, and contributing to the “Chinese plan” for the protection of black soil in the world.
A lot of important things happen quietly in the soil
Regardless of the low proportion of microorganisms in the soil composition, the powerful functions of the soil are inseparable from these small things.
The most important role of soil microorganisms is to decompose animal and plant debris and help nature recycle materials. Without these microbes, our planet would be a mountain of wreckage. It’s not just a matter of aesthetics: matter in nature is conserved, neither increasing nor decreasing, and if matter keeps accumulating in the remains without being released, there will be less and less matter available to the living, until life becomes extinct. Microorganisms decompose the organic matter that composes the organism into inorganic matter, and the inorganic matter can be reabsorbed and utilized by plants, etc., which realizes the ecological material closed loop.
Plant growth is inseparable from nutrients and microorganisms in the soil
The decomposition of microorganisms is also an important factor affecting soil water seepage and water retention capacity. Some organic substances can be converted into colloidal substances after being decomposed by microorganisms. These gelatinous substances are excellent soil binders and help promote the formation of clumps – soil aggregates. There are a lot of voids between soil aggregates, and these voids are both channels for water delivery and storage for water. In addition, the mycelium formed by the fungus can also help the formation of soil aggregates by entangling the soil particles. During the busy farming season, farmers work diligently to cultivate the land, use hoes, rakes and other tools to chop and squeeze the soil, supplemented by the “work” of microorganisms, which can avoid the reduction of soil aggregates and keep the soil loose.
Climate change is one of the challenges facing the world today, and maintaining the high water permeability of soils is of great significance to addressing this challenge. If the rainwater cannot be absorbed on the spot, but flows downstream, it will inevitably wash away some of the nutrients in the soil and affect the soil quality; in severe cases, it will directly swept away the soil, causing soil erosion. This damage to the soil is called “soil erosion”.
The content of organic matter (including microorganisms) in the surface soil is much higher than that in the deep soil, and the density of organic matter is smaller than that of inorganic matter (take a little soil and put it in a bottle, add water and shake, after a few hours, the inorganic particles will sink to the bottom of the bottle, while Organic particles float on the water surface) and tend to “go with the flow”. Therefore, of all soil layers, the topsoil is the most susceptible to erosion.
Once the microbial-rich topsoil is heavily eroded, the healthy growth of plants cannot be guaranteed. Photosynthesis of plants is a powerful driving force for absorbing carbon dioxide, and flowers and trees are the vanguards of absorbing greenhouse gases. Therefore, the positive significance of healthy soil in combating climate warming is self-evident.
Soil also makes cities safer
Most urban roads are impervious to water. Urban precipitation cannot penetrate into the ground in time, but can only be discharged along the sewers. If the drainage ditches and other facilities are not properly designed, it will be difficult to deal with the large amount of stagnant water formed in a short period of time. Therefore, in some cities, a little heavy rain is prone to waterlogging. To make matters worse, if the rainfall exceeds the capacity of the drainage system, the water in the sewers is very likely to back up. If the city does not separate the rainwater drainage system from the domestic sewage drainage system, in other words, the water used for flushing toilets and rainwater share the same pipe, and once the water overflows, the negative impact on our daily life can be imagined.
Urban flooding plagues residents
It is one of the effective means to solve the problem of urban waterlogging to make more land in urban areas have the ability to seep water and avoid the accumulation of water on the surface. Healthy soil is like a sponge. With the help of plants, rainwater gardens (naturally formed or artificially excavated shallow green spaces) and ecological wetlands can be easily stored underground through the soil, reducing the burden on urban drainage systems. Since the seepage capacity of the soil is closely related to the type and quality of the soil, urban construction personnel often “dig three feet” to judge the seepage status of the area by observing the color of the soil layer. At present, the urban construction department has opened up green spaces in many areas that have been inspected and qualified for water absorption. These green spaces are not only beautiful scenery in the city, but also efficient facilities for controlling rainwater inundation and utilizing rainwater.
95% of human food comes directly or indirectly from soil. Soil also makes a huge contribution to global biodiversity. The survival of 1/4 species is closely related to soil.
However, soil loss is like a sword hanging over the heads of all mankind. According to statistics, on average every 5 seconds around the world, soil the size of a football field is eroded or lost. According to the United Nations Food and Agriculture Organization, it takes an average of thousands of years to form 2 to 3 cm thick soil on the earth’s surface, but as much as 25 billion to 40 billion tons of topsoil is lost every year.
The overexploitation of the western part of the United States has led to black sandstorms in the grasslands, which made locals realize that a large amount of loose bare soil was blown up by the wind or washed away by water due to the ploughing of agricultural machinery. China has faced similar problems in recent years. In order to protect the important arable soil in my country’s agricultural production areas, Chinese scientists have begun to carry out relevant research by introducing “conservation tillage” (the core requirement is to carry out less/no-tillage sowing without ploughing the soil and covering the surface with straw) The mechanism allows harvesting and planting to be carried out at the same time, which largely avoids soil loss. It can be said that protecting the soil is to protect our rice bowls.