Although the area of cultivated land in China is less than 10% of the world total, the amount of chemical fertilizer application is close to 1/3 of the world total, which has become the main cause of agricultural non-point source pollution. At the end of autumn harvest and the beginning of wheat sowing, we should listen to the experts about the phenomenon of excessive application of chemical fertilizers in China.
"The problem of excessive application of chemical fertilizers does exist. It leads to serious soil acidification. The most obvious problem is the increase of heavy metals in the soil and the single organic matter. In general, it is soil malnutrition." Shi Weiming, a researcher at the Nanjing Soil Research Institute of the Chinese Academy of Sciences and director of the Research and Development Center for Non-point Source Pollution Control Technology, said.
Compared with the farmers who grow grain sporadically, the large farmers who grow grain use fewer chemical fertilizers because they take more into account the cost of agriculture. According to preliminary statistics, 80 kg of urea is needed for each mu of rice planted by large grain-growing households. However, scattered grain-growing farmers do not pay much attention to agricultural input, and some even double the amount of urea used by large households, resulting in about 70% of nitrogen fertilizer not being utilized, which not only improves the agricultural cost, but also makes agricultural non-point source pollution more serious.
Shi Weiming is worried about this phenomenon. Soil also has life and needs rest, he said. The overuse of chemical fertilizers, which is prevalent nowadays, actually makes the soil work very hard. Soil is very tired and will collapse over a long period of time. We can't just pay attention to yield, regardless of soil fertility and environment. Otherwise, it will be very difficult for grain to continue to increase production. "The collapse of soil fertility is not alarmist." Shi Weiming said that many vegetable fields in a major vegetable producing county in Shandong Province have been replaced in recent years because of large input of fertilizers for many years in order to achieve large output of vegetables. In European and American countries, in order to maintain soil fertility, fallow measures are often taken to restore the land. This is not very realistic in our country. Japan can continue to increase its grain output by controlling the amount of chemical fertilizer, but for the sake of food quality and environmental safety, it intends to reduce the use of chemical fertilizer and give the land a certain degree of rest, which we can learn from.
Another way to balance soil nutrients is to apply organic fertilizer. Wu Longhua, a researcher at the Center for Soil and Environmental Bioremediation, Nanjing Institute of Soil Sciences, Chinese Academy of Sciences, said the tests found that most of the cultivated land in China now has too much phosphorus and nitrogen fertilizer. Undigested phosphorus and nitrogen fertilizers can Eutrophicate nearby water bodies and cause water pollution such as cyanobacteria. Most cultivated land has less potassium fertilizer. In recent years, the application of straw returning to the field has improved the potassium fertilizer content. Among organic fertilizers, the content of potassium fertilizer is relatively high.
In the early years, the grass-roots agricultural technicians were relatively neat and the soil testing formula was better. In recent years, the brain drain was obvious. In a large agricultural county, there were often few people who knew soil nutrition. Farmers do not know much about fertility balance and what is missing in the soil. In order to increase yield, they often blindly increase the amount of chemical fertilizer. In fact, on the premise of balanced soil nutrition, if the use of 20% less chemical fertilizer, grain output will only decrease by 1%-2%. The cost saved is higher than the value of grain output. To make this clear to farmers, farmers will definitely reduce the use of chemical fertilizer. It is very important to have a professional agricultural technology team to help farmers apply fertilizer accurately and maintain soil fertility, which is related to the sustainability of increasing grain production in China. (Zhu Xinfa)