On March 11, 2011, Japan experienced the unprecedented Tohoku earthquake. It was the largest in Japan’s history, and created a massive tsunami that impacted Japan’s northeastern coast. A result of the earthquake and tsunami was the meltdown of the Fukushima Daiichi Nuclear Power Plant. This meltdown had immediate and long-term impacts on the area.
On February 13, 2021, just shy of a decade after the disaster, Japan was hit with a 7.3 magnitude quake—an aftershock of the same earthquake that caused the disaster at Fukushima Daiichi. At the time of publication of this article, Japanese officials have not identified any irregularities in their nuclear power plants, but residents along the coastline are wary.
Right after the accident in 2011, the Yamakiya area of the Fukushima prefecture was designated as a “Planned Evacuation Area” by the Japanese central government. About 1,200 people had to move out of their loving hometown, so they wouldn’t be exposed to radioactive Cesium that fell in their area. Yamakiya is a small and quiet mountain village area.
Many of them used to engage in agriculture before the Fukushima disaster. The soils of the area were also contaminated from radioactive Cesium. This radioactive Cesium has a half-life of thirty years. This means that it will take 30 years for half of the Cesium-137 to lose its radioactivity and turn into the safer form of barium.
Unfortunately, if food were grown in that soil contaminated with radioactive Cesium, the food would also be contaminated with radioactive Cesium.
While residents were still evacuated, the Japanese Ministry of Environment conducted a decontamination process. Surface soils contaminated with radioactive Cesium were mechanically removed, and fresh, uncontaminated new soil was added.
My research group began to study the soils of the Yamakiya region, Fukushima, in 2015. This is one of the areas where land was severely polluted by radioactive Cesium, as well as other contaminants.
The evacuation order was lifted in 2017. But by January 2021, only 343 people returned to their homes in Yamakiya. Lands are left without management. Fallow areas tend to be covered by grass and shrub weeds. We found that many uncultivated rice paddy areas were invaded by common reed.
Why have so few returned – and why aren’t they farming?
The government’s decontamination process gave Yamakiya two different consequences: recovery from radioactive contamination and severely lowered soil fertility. Regarding the radioactive contamination, the news is good. In most of the areas we monitored in Yamakiya after decontamination, the soils of residential and agricultural areas had safe amounts of radioactive Cesium. This means that removing the contaminated soils solved the issue of continuous radiation exposure in the Yamakiya area, and it was safe for human residents. That’s why they were able to return in 2017.
On the other hand, the surface soil was not healthy for growing food from a soil fertility aspect. For example, one farmer’s vegetable field in Yamakiya showed very low carbon content after the decontamination process. The total carbon amount in the soil decreased by 75%. Soil carbon, referred to as soil organic matter, plays several critical roles in growing healthy crops. In addition, the ability of the soil to hold and release cations decreased by 48%. This is also important because fertilizers are applied as salts (usually nitrates) that are held and released in an electrical exchange between soil particles and plants.
Soil organic matter plays many important roles in an ecosystem. It provides soil a chemical buffer, supplies elements for plants, supports physical environment, and gives microbes food. In the soils where decontamination took place, this soil organic matter content is extremely low.
To restart cultivation in such areas, we must increase organic matter content in soils. In many suburban areas in Japan, farmers use livestock manure that contains lots of organic carbon and other nutrients. These areas have close-by sources of manure that makes this an economical means to improve soil health.
However, in the areas affected by radioactive contamination by the Fukushima disaster, there are few places where the livestock industry has restarted and come back to the level before 2011, and availability of livestock manure tend to be low.
Our team thought that we might be able to use green manure instead. In 2017, we started experiments to test the soil-recovering effects of green manure in Yamakiya. We grew and incorporated rye, hairy vetch, and sorghum four times for 2 years. Concentrations of radioactive Cesium was mostly under detection level for these plants and decontaminated soils.
The green manure incorporations were effective to improve soil physical conditions. Rye incorporation increased pore space by about 20%. Also, available nitrogen was increased by incorporating hairy vetch. On the other hand, soil organic matter content and the ability to hold and release cations did not significantly change.
We concluded that green manure helps to recover soil fertility to some extent. But for substantial recovery, we needed to apply more organic matter to soil in decontamination zones.
Building on this idea, we compared the effects of chemical fertilizer and cow manure on plant growth in a typical Japanese upland soil (Andosol) versus the soil in Yamakiya after decontamination. We did a small-scale experiment in pots.
We found that even if we provide chemical fertilizer to nutrient poor Yamakiya soil, we could not grow healthy plants. Cow manure application increased root and aboveground biomass of plants. To this end, we need more studies to see how organic matter can recover these decontaminated soils for a longer period.
During our three-year research project, we were impressed by the kind people in Yamakiya. In such a quiet and peaceful area, people used to live with nature. They went into surrounding forests to collect leaves to put into their gardens. Mushrooms in forests were their favorite foods. These lives never come back. We were strangers when we first visited Yamakiya, a few young students and a middle-aged woman from the Tokyo area. Yet they always welcomed us and let us do research in their land. Even more, they took care of us, told us how to cook their country food, and taught us something very important. They never give up and stand up for something better and keep their lives in Yamakiya. Our full respect to these people motivates us to make progress and step forward to a better world based on soil science.
Answered by Miwa Yashima Matsushima, Chiba University
About us: This blog is sponsored and written by members of the American Society of Agronomy and Crop Science Society of America. Our members are researchers and trained, certified, professionals in the areas of growing our world’s food supply while protecting our environment. We work at universities, government research facilities, and private businesses across the United States and the world.
To read more about Fukushima, read these blogs: