In early July, Huang Daoyou, a researcher at the Institute of Subtropical Agriculture and Ecology, Chinese Academy of Sciences, flew to Yunnan with his team ’s research results to explain how to use the “VIP + N technology model†to realize the vision of producing rice safely in farmland with heavy metals exceeding the standard. .
This team, which has been committed to farmland pollution and food security since the 1990s, has slowly integrated millions of acres of contaminated farmland to produce food with more than 10 years of technology integration in Hunan and other places.
Contaminated land
In April 2014, the then Ministry of Environmental Protection and the Ministry of Land and Resources jointly issued the "National Bulletin on Soil Pollution Survey" (hereinafter referred to as the "Bulletin").
The “Communicationsâ€, which was made public after eight years of investigation, said that the 6.3 million square kilometers of soil surveyed on the spot showed that the national soil environment is generally not optimistic. The soil pollution in some areas is relatively heavy. The quality of the cultivated soil environment is worrying. Environmental problems are outstanding. The national soil over-standard rate is 16.1%, and the soil over-standard rate for cultivated land and forest land has reached double digits.
Many environmental protection experts in universities and business circles in Hunan pointed out that the pollution of cadmium, mercury, and arsenic heavy metals is more serious in the south of the Yangtze River, and Hunan is no exception. Chen Nengchang, a researcher at the Guangdong Institute of Eco-Environmental Technology, believes that China's soil cadmium content has increased from an arithmetic mean of 0.097 mg / kg in 1990 to 0.3 mg / kg in 2014, indicating that a large amount of pollutant cadmium has entered the soil.
Where does soil cadmium pollution come from? Chen Nengchang pointed out that for many years, as a "world factory" in China, metal smelting areas are extensive and large, coal is the main energy source, coupled with poor implementation of pollution prevention and control laws and measures, the rate of cadmium exceeding the standard of soil pollution has become protruding. From a spatial perspective, China ’s annual emission of cadmium into the atmosphere is as high as 2186 tons, and it is estimated that the annual amount of cadmium entering the farmland is as high as 1417 tons. Among them, 178 tons of cadmium is taken away by various channels every year, and the remaining 87% is retained In the soil of farmland.
It is understood that when the environment is contaminated with cadmium, cadmium can be enriched in the organism and enter the human body through the food chain to cause chronic poisoning. Patients with cadmium injury are prone to diabetes, proteinuria and amino acid urine. The absorption of cadmium will hinder the metabolism of bones, resulting in a series of symptoms such as osteoporosis, atrophy, deformation, etc., which will lead to osteomalacia and body pain, called "painful disease". In addition, chronic cadmium poisoning also has an impact on human fertility. It will seriously damage the Y factor, making the babies born mostly female.
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Seeking solutions
Huang Daoyou, the chief expert of the project "Safe Use of Heavy Metals in Farmland Exceeding Standards" of the National Science and Technology Support Program, told the China Youth Daily · China Youth Online reporter that as early as the 1990s, there were signs of heavy metal pollution in farmland. However, because the problem was not very prominent, and the domestic concern at that time was whether food was enough, the problem of pollution was not put on the agenda.
In the new century, the cadmium pollution incident in the Majia River in Zhuzhou, the cadmium and lead pollution incident in the Phoenix Pb-Zn mining area, the cadmium, lead and arsenic pollution incident in the Taojia River Basin in Chenzhou, and the cadmium pollution incident in Zhentou, Liuyang ... A series of agricultural product quality and safety issues have become the focus of public and government attention. Nationwide, heavy metal-contaminated food alone amounts to 12 million tons per year, causing direct economic losses of more than 20 billion yuan.
Guo Zhaohui, a researcher from the Hunan Provincial Institute of Microbiology, said that there are many cadmium and arsenic in heavy metals in Hunan Province, and the country attaches great importance to this. For more than three years, more than 4 billion yuan has been invested in Changzhutan area for research, hoping to find a way to control it. And promoted nationwide.
He pointed out that in the field of agriculture, for the treatment of heavy metal pollution, due to the high frequency of land cultivation and the pressure of food production, the soil cannot be idle for a long time for treatment. Therefore, the focus is to reduce the adsorption of metals to a certain degree of control. The existing cultivated land in China is divided into key protected areas, safe use areas and strictly controlled areas. The former is a safe and reliable main grain production area. Strictly controlled areas can only be managed by adjusting plant varieties. The safe use zone is the direction that the country expects to break through.
It is reported that the requirements of this plan are that priority must be given to adopting agronomic control under the "three unchanged" conditions of "keeping the current crop planting system unchanged, ensuring that farmers’ planting habits are not changed, and ensuring that farmland use is not changed. " , Passivation and other technical measures to reduce the effectiveness of heavy metals in the soil and reduce the content of heavy metals in edible agricultural products to ensure the production of edible agricultural products up to standard.
To this end, Hunan Provincial Agricultural Department organized domestic and foreign enterprises and scientific research institutes to establish dozens of test areas. "Everyone is showing their ability. The key is to reduce the cadmium content in rice." Guo Zhaohui said, the final result is that the comprehensive technology model of VIP + N stands out from the crowd.
VIP ＋ N
The chief expert of this technology, Huang Daoyou, introduced that the so-called VIP + N technology is: the research of polluted rice fields was jointly conducted by the Institute of Subtropical Agricultural Ecology, Chinese Academy of Sciences, Hunan Agricultural University, Hunan Academy of Agricultural Sciences, Hunan Agricultural Resources and Environmental Protection Management Station, etc. The characteristics of cadmium morphology changes constitute a rice cadmium pollution control technology system of "low cadmium varieties (Variety) + full growth period flooding irrigation (Irrigation) + application of quicklime to adjust soil pH (pH) + auxiliary measures (N)"
Initially, researchers focused on determining biological control methods—that is, using the differences between the types or varieties of heavy metals absorbed and accumulated by crops, using crops that have a low accumulation of heavy metals, and lightly to moderately polluted soils with heavy metals For agricultural production.
There are rice varieties with low cadmium accumulation, but in the face of cadmium-contaminated soil, researchers further consider experiments on irrigation and soil pH, hoping to explore effective empirical parameters.
"To absorb as little as possible, one is to passivate the activity of heavy metals. Just like pulling a rope to a cattle, let it run or slow down and lose vitality. The other is to do agronomic regulation, such as irrigation and PH regulation. To start, make the cadmium movement environment worse. "Huang Daoyou said that flooding irrigation during the whole growth period of rice can make cadmium react into a precipitate of cadmium sulfide. They selected the early rice variety Jiayu 948 and the late rice variety Zhongyou 218, respectively. They were combined with conventional treatment, flooding during the whole growth period, and re-flooding during the middle booting period after the sun, and found that the water management measures in different fields affected rice Cadmium accumulation has a great impact.
The researchers also found that when the soil pH is less than 6.5, for every increase in soil PH unit, the effective cadmium content in the soil can be reduced by 0.1 mg / kg. Soil pH was also significantly negatively correlated with the accumulation of cadmium in rice, that is, for every soil PH unit increased, the cadmium content in rice could be reduced by 0.12 mg / kg.
Foliar control technology through foliar application of certain substances (iron, zinc, silicon, etc.) to improve crop resistance to heavy metals and reduce or even block the transfer of heavy metals to the food chain has also been proven in practice to reduce Cadmium is partially transferred to the grain of rice.
According to reports, VIP + N technology can reduce the cadmium content of rice to less than 0.2mg / kg stipulated by national standards.
Huang Daoyou said that in the past, researchers mostly ran in low-accumulation crop breeding technology, agronomic regulation, in-situ passivation, etc., but this set of technical models has not been systematically refined.
At a research meeting in 2013, an expert from Hunan Agricultural University intercepted the first English letters of various technologies and condensed them into "VIP + N". This technology was named.
The widespread implementation of farmland depends on the ability and motivation of farmers
The reporter learned that the “Changzhutan Heavy Metal Contaminated Cultivated Land Rehabilitation and Industrial Structure Adjustment Pilot Project†initiated by the Ministry of Agriculture and the Ministry of Finance has been officially implemented since 2014. In that year, VIP + N test areas were established in various places in Hunan Province.
"In the beginning, it was a community trial. We experts went to the field to do it ourselves to control the effects." Huang Daoyou said that in 2015, this project began to be extended to 19 counties and districts in Changzhutan, and 50 100-mu demonstration fields were established; The area exceeds 600,000 mu. In 2016, the Hunan Provincial Agriculture Commission and the Hunan Provincial Department of Finance issued a document to promote this type of standardized demonstration film in the province. A total of 1.8 million mu was arranged in 26 counties and cities, of which 26 thousand mu demonstration film + 1 million mu demonstration film.
He said that the effect of many years of practice shows that the use of this technology can reduce the cadmium content of rice by more than 60% on average, especially in the application of acidic mild cadmium contaminated rice fields. The rice compliance rate is more than 90%.
Guo Shuai, president of Taigu Group, who undertook heavy metal-polluted farmland restoration and management projects in 19 project counties in the Changzhutan area and 7 projects in the upper, middle and lower reaches of the Xiangjiang River, told China Youth Daily · China Youth Online reporter that the State Council officially released in May 2016 The "Soil Pollution Prevention and Control Action Plan" proposed the safe use of polluted cultivated land, requiring the publication of a technical guide on the safe use of contaminated cultivated land by the end of 2017; by 2020, complete the safety of light and moderately polluted cultivated land of 40 million mu use. From their years of experience, this set of technical models has been applied on the basis of accurately clarifying the status of soil pollution and the over-standard situation of agricultural products, and the actual combat results have been excellent. If supplemented with soil conditioner and organic fertilizer, the effect can be further improved. However, during operation, it is also affected by factors such as a low number of low-cadmium accumulated varieties, uneven precipitation time of farmland, and severe seasonal drought.
Researcher Guo Zhaohui pointed out that the national standard for rice contains less than 0.2mg / kg of cadmium, and its requirements are much higher than the EU standard of 0.4mg / kg, which is also stronger than that of neighboring Japan.
It is reported that in the promotion of the Changzhutan area in 2015, the 100-mu demonstration field adopted the method of government purchasing services-that is, enterprises use technology to organize agricultural production, and the government pays after testing the effect.
Guo Zhaohui proposed that the VIP + N technology model is relatively mature and effective for the treatment of cadmium pollution in rice. However, it is widely implemented in farmland, and large experimental samples show that the effect depends on the ability and enthusiasm of the “responsible subject†farmers.
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