Deciphering the black land

The fragrance of rice flowers in black soil

There is a saying in the geological industry that "look at the color and recognize the composition". The black soil is black because it contains more dark black humus. Humus can not only provide rich nutrients such as nitrogen, phosphorus and sulfur for plant growth, but also make black soil have a unique structure-aggregate structure. Humus, like glue, binds soil particles into aggregates of several millimeters, which are called small reservoirs and small fertilizer reservoirs of plant roots, which are unmatched by clay, sand and other properties. Therefore, the black soil has high fertility and good character, which is worthy of the reputation of the king of the soil.

When we usually mention the black land, we can think of the northeast, so why is the black land only distributed in the northeast? the answer is most directly related to the climate of the four distinct seasons in the northeast. With the coming of summer, the rain and heat are in the same season, the vegetation grows vigorously, and the accumulation of organic matter on the surface is very large. In autumn and winter, the temperature drops suddenly, and the organic matter is covered with snow before it has time to decompose. When the temperature rises in the second year, microbes convert plant residues into humus and accumulate in the soil. Day after day, year after year, today's black land is formed! Studies have shown that it takes at least 200 years to form a 1 cm thick black soil layer.

Black soil profile in Hailun City, Heilongjiang Province

In the 4.6 billion years since the formation of the earth, only four major black soil belts have been created for us. In addition to the northeast plain of China, the black land is also distributed in the Mississippi Plain of the United States, the Great Plain of Ukraine and the Pampas grassland of South America. From the geographical location, it is not difficult to find that four pieces of black land are distributed in the middle latitudes, it is due to similar climatic conditions, as well as biological, hydrological and other joint action, created these black land. Because the black soil is fertile, it is an important agricultural base in the country. However, due to excessive reclamation and predatory management, black soil has been degraded to varying degrees.

Both the United States and the Great Plains of Ukraine have experienced "black storms" due to large-scale destruction of grass and reclamation of wasteland. On May 12, 1934, a huge storm swept across the vast expanse of the eastern United States and western Canada. The storm began in the most severely damaged arid areas of the western United States, and strong winds swept the dust, blocking the sun, and swept eastward. The storm lasted three days and more than 300 million tons of soil was blown away by the storm. Where the storm passed, wells and streams dried up, cattle and sheep died in large numbers, people were displaced and displaced, and the North American continent was desolate. This was the North American black storm that shocked the world at that time. North American black storm is listed as one of the top ten natural disasters of the 20th century.

Every time human beings win over nature, nature has to respond accordingly. After the black storm in North America, the Soviet Union failed to learn the lesson of the United States, and the tragedy happened again. In March and April 1960, the newly reclaimed areas of the Soviet Union (including the Great Plains of Ukraine) were eroded by black storms twice, and the farms that had been operated for many years were destroyed in a few days. Until the mid-1960s, on the basis of summarizing the large-scale reclamation, the Soviet Union took a series of measures to bring the black storm under control.

Soil sampling

Of the three black lands in the northern hemisphere, two have been damaged by black storms due to overreclamation. Can the black land in northeast China survive? the black land in the northeast is slightly different from the black land in the United States and Ukraine, the latter is mainly plain, flat, less sloping land, mainly eroded by the wind, easy to produce storms. While the northeast black land is sheltered by small and Daxing'an Mountains on the east and west sides respectively, and the most typical black land is distributed on the platform and hilly land in the east of Songliao Plain, with undulating topography, weak wind erosion and strong water erosion, so the probability of black storm in the black soil area is relatively small. However, the development of the northeast black land was much later than the other two black lands, and the large-scale reclamation began in the 1950s. In recent years, the black soil has also been seriously degraded, and there are many ecological problems, such as fertility decline, saline-alkali consolidation, soil erosion and so on.

So, what is the "physical" condition of the black land in the northeast of China?

The report shows that the black land in Northeast China is clean and basically free of heavy metal pollution, which can produce safe and secure food for us. What is more gratifying is that geological engineers have also found a large number of natural green and selenium-rich black land in Hailun City, Fujin City and other areas of Heilongjiang Province. Changfa Village in Hailun City has also made use of precious selenium-rich black soil resources to create "the first selenium-rich village in Longjiang". It promotes agricultural development and increases farmers' income, turning black soil into "black gold".

However, the northeast black land is also a little sick! The condition of the black land can be seen as "thin", "thin" and "hard". First, the black land has "lost weight". Compared with the data in the 1980s, the content of soil organic matter in the Northeast Plain has decreased by about 13%. The low content of organic matter leads to the decrease of soil fertility and the weakening of water and fertilizer conservation capacity. Farmers say that now the black land is becoming more and more "greedy" and there are more and more chemical fertilizers. Second, the black land is "thin". There are many sloping farmland on the black land in Northeast China, and it is easy to form surface runoff after rain, resulting in soil and water loss. According to the statistics of relevant departments, the area of soil and water loss in the northeast black soil area is more than 270000 square kilometers, forming more than 290000 large-scale erosion ditches. At present, the average thickness of the black soil layer of cultivated land in the northeast black soil region is only about 30 cm, which is about 40 cm less than that at the beginning of reclamation. Some areas have become thin black soil with low fertility, and some even reveal the loess at the bottom, which is commonly known as "broken skin yellow" black soil by farmers. Third, the black land has become "hard". Under the influence of water erosion, wind erosion and rolling of agricultural machinery, the aggregate structure of black soil is degraded, the soil is hardened and hardened, and it is difficult for crop roots to make use of deep soil water and nutrients, which reduces the coordination ability of soil, water, fertilizer, air and heat.

Rice paddy field in Sanjiang Plain

Know the disease, explore the cause, and the ultimate goal is to cure the black land and return the black land to health.

The CPC Central Committee and the State Council attach great importance to black land protection in Northeast China, and have successively implemented fertile soil projects, soil testing and formula fertilization projects. In 2017, the Ministry of Agriculture, together with the National Development and Reform Commission, the Ministry of Finance, the former Ministry of Land and Resources, the former Ministry of Environmental Protection, and the Ministry of Water Resources, formulate