Dr. Zhang Fusuo is a plant nutritionist at College of Resources and Environmental Sciences, China Agricultural University. His current research work focuses on soil nutrient management and its impacts on plant nutrient use efficiency and soil quality by combining rhizosphere processes and biological approaches.
Chinese agriculture has intensified greatly since the early 1980s-- making the country the world's largest cereal producer, for example-- in large part because farmers have ramped up their use of chemical fertilizers. New findings show a serious drawback to the use of nitrogen fertilizer in China: it has caused the soils to become significantly more acidic, which in the long term reduces their ability to support life.
What is the central conclusion of your study?
The central finding of our study is that since the 1980s, soils in major Chinese croplands (aside from the "Aeolian soils" in the Northwest) have exhibited striking, across-the-board acidification. This sort of regional soil acidification is virtually inseparable from China's agricultural intensification of the last 20 years, especially the excessive use of chemical nitrogen fertilizers. The decrease in cropland quality caused by soil acidification threatens China's future food security and the sustainable development of its agriculture and environment.
How much more acidic is soil across China now than it was in 1980, the baseline year for your study? Where and under what conditions have the problems been most pronounced?
Compared to the early 1980s, the average pH level of Chinese cropland soil has fallen by 0.5 units, equivalent to a 2.2-times increase in soil acidity. Looking at the range of decrease in pH levels, soil acidification in China is most pronounced in the "red soil" regions of the South, the "purple soil" regions of the Southwest, and the "black soil" regions of the Northeast. The problem of soil acidification is much more serious in high-intensity cash crop systems (for example greenhouse vegetable and fruit production) compared to the traditional cereal crop systems.
What are the major contributors to soil acidification within China?
The major contributor to cropland soil acidification within China is the excessive use of nitrogen fertilizers in agricultural production. Over the last 20 years, the long-term, unreasonably excessive use of these fertilizers has led to decreased nitrogen use efficiency and to a large surplus of nitrogen fertilizers in the soil. Excessive nitrogen fertilizers in the soil result in a large amount of nitrate leaching, making soil acidification even worse. In addition to this, as crop production increases, the uptake of base cations by harvested crops, straw and other plants increases without ceasing. Therefore the rapid decrease in crop residues returned to the field is another important reason leading to soil acidification.
Were the results at all surprising? What took you most by surprise?
Yes, the results we obtained really shocked us. First, under natural conditions, soil acidification is a long, slow process. But in little more than 20 short years, China's cropland soil underwent acidification that would have-- under natural conditions-- taken several hundred or even a thousand years to achieve! What shocked me most was that our results showed a clear and unexpected decrease in pH levels for the calcareous and alkaline soils of Northern China, long believed to be insensitive to acidification because of its natural buffering qualities. This shows that the carbonate salts and acid-buffering components inherent in the soil have already been largely used up. Once these buffering components are completely used up, the speed of pH decrease or acidification in these soils will increase significantly.
What are the implications of your research?
The results of our research systematically reveal the long-ignored problem of regional cropland acidification and its reasons. Most past research considered the burning of fossil fuel leading to acid deposition (via sulfur and nitrogen deposition) to be the major reason for soil acidification. In addition, most of this research was limited to forest soils. Our research shows that in contrast to acid deposition the unreasonable use of nitrogen fertilizers in intensive agricultural production is the main reason that accelerates soil acidification. Our research has important theoretical and practical implications in establishing a model for sustainable development in both agricultural production and environmental protection.
Is there any way to reverse or at least mitigate the problem of cropland acidification in China?
Presently, there are a number of ways to reverse or mitigate the problem of cropland acidification in China. First, we should use scientifically-sound methods of fertilization in order to decrease the unreasonable amount of nitrogen fertilizers used in agricultural production, and from this basic level cut off the cause of soil acidification. Second, we should combine mechanization and other methods to widely promote technologies that will return crop residues to the field, thereby allowing these crops to return to the soil the base cations they previously took from the soil. Third, in soil that is already seriously acidified, we should use reasonable amounts of lime or other alkaline materials to raise the pH level of the soil and correct soil acidification.
These are Dr. Zhang Fusuo's written remarks. Please refer to the video interview for exact quotes.
Related Research Papers
Significant Acidification in Major Chinese Croplands
Press release: Chinese soils acidifying due to fertilizer