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Across China, soil degradation and urban expansion have piled the pressure on farmland, threatening both quantity and quality

By Wang Yan , Liu Xiangnan Updated Sept.1

Soil conditioners are used to treat soil acidification in Yiqiao Village, Jiangxi Province, March 5, 2021

In 2018, farmer Liu Zhihua in Qiyang County, Hunan Province watched helplessly as the price for the rice he grows plunged. Since 2013, it had been hard to sell rice produced in parts of Hunan after the soil was found to contain excess levels of heavy metals, particularly cadmium, a result of industrial pollution and excessive use of fertilizers on already acidified soil.  

According to Zhang Huimin, a researcher at the Institute of Agricultural Resource Regional Planning, soil already contaminated with heavy metals by overuse of fertilizer can multiply soil acidification and pollution. “In some areas, they applied too much fertilizer, which caused nitrification of nitrogen compounds in fertilizer elements in the soil, and this process is acid-producing,” Zhang told China Central Television (CCTV) in June. If the soil already contains high levels of heavy metals and then becomes acidified, some of the dormant heavy metals become active, accumulate in crops and cause heavy metal pollution of the harvest, Zhang said.  
In the past 30 years, due to acid rain and excessive fertilization, farmland in large areas of southern China have become more acidic.  

At the same time, areas in northern China suffered from soil salinization. “Salinization and acidification are types of soil degradation,” said Li Baoguo, dean of the School of Land Science and Technology, China Agricultural University. “Degraded black soil lands in northeast China also face problems of salinization and desertification,” he told NewsChina.  

According to the CCTV report, areas of degraded black soil land in northeastern China, acidified soil in southern China and salinized soil in northern China total 660 million mu (440,000 square kilometers) of farmland, more than a third of China’s arable land. 

Acid and Salt 
In 2010, an article titled “Significant Acidification in Major Chinese Croplands” published in Nature by Chinese scientists evaluated changes in soil acidity after long-term monitoring and soil surveys. The article finds that “soil pH declined significantly from the 1980s to the 2000s in the major Chinese crop-production areas.”  

Weng Boqi, a researcher at the Fujian Provincial Academy of Agricultural Sciences, has researched soil acidification since 2016. Weng told NewsChina that 293 million mu (19.5 million hectares), of China’s arable land is acidic with a pH of less than 5.5. This accounts for nearly 20 percent of the country’s cropland. On the pH scale, 7 is neutral, readings below that indicate acid, and a reading of above 7 indicates a substance is alkali.  

Acidification has two major causes: natural and artificial acidification, Weng said. In terms of long-term soil development, conditions including high temperatures, high humidity and heavy precipitation speed up soil acidification, therefore due to prevailing climate and weather patterns, the acidic soils of southern China and the neutral to alkaline soils of northern China form naturally.  

However, artificial acidification has significantly accelerated this process due to the excessive use of nitrogen fertilizer.  

The southeastern Chinese province of Fujian faces serious soil acidification. Weng said that data released in 2015 by the National Agricultural Technology Promotion Service Center indicated that the average pH value of soil in Fujian is the lowest in the country, only 5.36, while most farmland has a pH value of below 5.5, accounting for about 74 percent of the arable land nationwide.  

Fujian is a subtropical region with a marine monsoon climate, high temperatures and year-round rains. Soils in high rainfall regions tend toward greater acidity. Weng said that when the amount of precipitation exceeds evaporation, soil leaching occurs. This means the soluble material becomes detached from the soil and is carried away by the runoff water. Buffer substances present in the soil, which have weak acidity and act to prevent changes in pH, are also washed away, which exacerbates soil acidification.  

Fujian is rich in agricultural and forestry resources, and a major producer of cash crops. As farmers try to increase yields and economic returns, they increasingly apply nitrogen fertilizers, which accelerates the process of soil acidification.  

Soil salinization mainly occurs in northern China, said Li Baoguo of China Agriculture University, who has been studying it since the 1980s. “Low-lying areas in northern China are all saline. Once you cross the Huaihe River to the south, there is almost no saline-alkali land,” Li said.  
Salinization is first a natural phenomenon, although human activities are major contributors. Chinese farmers expand irrigated areas to increase productivity. When moisture from irrigated fields evaporates, it leaves salt behind. In coastal or arid areas where soil is already prone to salinization, this process only makes it worse.  

“In the north, you need to control irrigation or you’ll get salinization,” Li said. “Irrigation water differs from natural precipitation. It contains 10 or even hundreds of times more salt. After irrigating farmland with water diverted from the Yellow River, some regions in Shandong and Henan provinces saw rapid soil salinization,” Li said. However, treatment measures for the previously widespread salination have improved the situation in the saline-alkali lands across northern China.  

Overuse of chemical fertilizers and pesticides has lowered the quality of farmland around the country. In 2016, in terms of the total land cultivated with crops, the use of chemical fertilizer per hectare was 360 kilograms, nearly 60 percent higher than the international safety limit of 225 kilograms per hectare. Long-term excessive use of chemical fertilizers and pesticides causes nutrient imbalances, the decline of soil fertility and soil organic matter, and environmental pollution. 

Bigger Cities, Less Farmland 
Urban construction and expansion of protected land challenges the already limited cultivated land resources. The situation worsened from 2009 to 2018. A policy to offset taking away agricultural land for construction around urban areas means finding an equivalent amount of land elsewhere, so previously uncultivated land is developed for farming.  

Also, the Grain for Green ecological restoration project, which encourages farmers on marginal land to swap farmland for trees to combat deforestation, along with agricultural adjustments and natural disasters, significantly changed the quantity, quality and distribution of China’s cultivated land.  

According to the third national land resource survey conducted from September 2018 to December 2019, the total area of farmland area fell from 2.031 billion mu (135.4 million hectares) in 2009 to 1.918 billion mu (127.9 million hectares).  

In January 2021, a paper titled “Regional Characteristics and Evolution of China’s Farmland Changes in the past 10 Years” published in the Journal of Agricultural Engineering analyzed changes in cultivated land from 2009 to 2018. The conclusion was that the overall amount of cultivated land area in China is stable, but regional changes vary significantly. 
Through analysis of the dynamics of cultivated land change, researchers found that cities, provinces and regions such as Beijing, Tianjin, Shanghai, Chongqing, Guangdong and Xinjiang Uygur Autonomous Region changed more significantly. Among the six regions, the amount of cultivated land in Beijing, Tianjin and Chongqing decreased most significantly, while the changing dynamics of cultivated land in Shanghai, Guangdong and Xinjiang increased significantly.  

Prior to 2010, experts thought the Pearl River Delta in Guangdong and the Yangtze River Delta near Shanghai faced the most serious farmland loss in China. But in the past decade, China’s central region has suffered the most serious farmland loss, and the cultivated areas in Guangdong and Shanghai have increased significantly.  

Researchers found that the decrease in cultivated land in China occurs mainly within 30 kilometers from central urban areas, while newly cultivated land mainly appears 40 kilometers from the urban center. They concluded this shows that urbanization is still the dominant factor in the decline of arable land.  

Arable land in 22 out of 31 provincial regions decreased by a combined 709,100 hectares. In the other nine provinces and regions, the arable land area increased by 315,400 hectares. “This shows that the policy goal of a dynamic aggregate balance is being basically achieved, but there are still regional differences,” Weng said.  

Wei Houkai, director of the Institute of Rural Development, Chinese Academy of Social Sciences (CASS), told NewsChina that industrial and urban construction is the main reason for the decline in crop land area. Comparing data from the country’s second national land resource survey from 2007 to 2009 with the third national land resource survey from 2017 to 2019, urban, industrial and mining areas increased by 22.9 percent, and the land used for transportation increased by 20.3 percent, and this took away arable land. The second cause is ecological projects such as Grain for Green. From 2009 to 2019, forest cover increased by 11.9 percent.  

Statistics indicate that per capital arable land has continued to decline over the past 40 years from 1.59 mu (1,060 square meters) per person in the 1980s to 1.36 mu (907 square meters) per person now. Li Baoguo said he does not feel optimistic as arable land continues to decline and he cautioned that the amount of good quality arable land has reduced quickly. “Once urban development encroaches on high-quality farmland in the suburbs of cities like Shanghai, Suzhou and Wuxi, it will permanently disappear,” Li said.  

Fragmentation of arable land operation and low economic benefits for farmers only increases the pressure on arable land preservation. In southwest China and China’s southern coastal regions, authorities have zoned extensive areas of cultivated land for non-agricultural use. 
Li Renqing, secretary-general of the Rural Social Issues Research Center, Chinese Academy of Social Sciences, told NewsChina in June: “Along with modernization, industrialization and urbanization, land use has been changing continuously. Farmers can barely make money, so it’s common to see them giving it up or not using the land as efficiently as they could.” 

A farmer plows the red soil in Dongchuan, Yunnan Province on May 29, 2016. The low-yield red soil developed due to high temperatures, rain, and high iron content, as well as deforestation

Scientists take samples on land affected by salinization in China’s northwestern Qinghai Province

Arable land is replaced by new buildings and urban construction in Jiangbei District, Nanjing City, Jiangsu Province, May 22, 2021

Farmers spray fertilizers in Fuxi Village, Anhui Province, February 16, 2022

Soil Incentives 
According to Weng, Fujian Province has ramped up prevention and control measures to address soil acidification and is providing guidance to farmers on better use of fertilizers, including organic fertilizer. The province is attempting to rectify its acidic soil, such as applying biochar (black carbon) in tea gardens, and promoting the use of lime and organic fertilizer in orchards. 

The Ministry of Agriculture issued the Action Plan for the Protection and Improvement of Cultivated Land Quality in 2015, which prioritized dealing with acidified land in southern China. Pilot areas saw lime and soil conditioner applied, as well as conservation tillage to plow back crop stubble into the land and use of organic fertilizer.  

During the 14th Five-Year Plan (2021-2025), the Ministry of Science and Technology allocated funds to support management and prevention of acidic soils, and technological innovation. Campaigns and action plans with slogans such as “zero growth of chemical fertilizer” and “replacing chemical fertilizer with organic fertilizer for fruits, vegetables and tea” have been implemented at the national level.  

Rural issues expert Li Renqing believes that farmers’ interests have to be taken into consideration to address the structural change in land use. He suggests considering how to reduce labor costs while increasing farmers’ incomes.  

“Apart from arable land reduction, the biggest threat to food safety and food security is overuse of arable land, which results in destruction of organic matter and the acid-base equilibrium,” Li said.  

“Due to excessive use of fertilizer and continuous soil and environmental pollution, a significant amount of arable land becomes unfit to farm, which threatens the sustainable use of arable land for future generations. The problem is very serious, but it’s still not getting nearly enough attention,” he said.  

Liu Liming, a professor at the School of Resources and Environment, China Agricultural University, told NewsChina that “China’s cultivated land protection has been effective, or at least we have basically safeguarded the arable land, yet problems in the quality of cultivated land remain.” Liu emphasized that more needs to be done to increase production capacity.  

Since implementing the household responsibility system to give farmers their own plots of land, farmland management, which includes utilization and protection of cultivated land, lies in the hands of farmers. In order to better protect farmland, Weng believes that farmers with good output or well-maintained land should be rewarded. He suggested setting up reward criteria based on testing organic matter levels in the soil once every five years. 

“We should have farmers protecting the farmland while maintaining soil fertility, and then promote the adoption of arable land quality conservation technologies,” Weng said.  

In 2017, Hunan Province carried out a pilot project in eight counties to replace chemical fertilizer with organic fertilizers. By 2019, 145 million yuan (US$21.5 million) in subsidies had been allocated to farmers. In 2020, they added four new pilot counties and provided subsidies, government procurement and the construction of fertilization facilities.  

Hunan farmer Liu Zhihua has used organic fertilizers under expert guidance since 2018. In spring 2020, the agricultural department provided free organic fertilizer and soil conditioners.  
After years of soil management, Liu saw improved soil fertility and better quality rice. Liu Zhihua told CCTV in the June program he was again confident about selling the rice he grows.