Radioactivity monitoring before and after decontamination is necessary to confirm the degree of success of farmland decontamination. In this paper, we describe a measurement system for rapid and accurate surveying of radioactivity of contaminated farmland using airborne gamma-ray spectrometry and a monitoring technique using a radio-controlled mobile vehicle combined with this system. The total weight of this measurement system, which uses a NaI(Tl) scintillation detector, is about 5 kg, making it sufficiently light to be installed in unmanned helicopters, balloons and other mobile vehicles used in this study. The use of a high-sensitivity detector allows sufficient measurement accuracy to be obtained with 10 seconds of measurement, and measurement can be performed while in motion. This system can also record information on measurement points while taking measurements, so the spatial distribution of gamma-ray intensity can be acquired. The obtained measurement data can be converted into air dose rates. The survey results at the two experimental sites confirmed that the air dose rates decreased after decontamination. These results show that the monitoring technique has sufficient resolution for evaluating the extent of decontamination effects on farmland and can provide visualized and easily understandable information on the radioactivity of farmland before and after decontamination.

Restoration and reconstruction is the greatest and most pressing task following a nuclear accident. In this paper we examined the task of reducing external exposure to radiation from radioactive material that has accumulated in agricultural land or its peripheral areas. We focus on the features of a machine for decontaminating agricultural peripheral areas such as embankments and agricultural roads, and we also report the results of onsite testing. Agricultural tractors with a shielded cabin were developed for decontaminating paddy fields that have been contaminated with radioactive material. The developed machines reduced the radiation dose rate of the interior of the cabin by approximately 50% or less from outside. The dust concentration was also reduced by more than 95%. The performances of the machines and the effects of the removal of surface soil were estimated via a decontamination test in Iitate, Fukushima. To reduce radioactive-cross contamination in rice huskers, we investigated two techniques: “decomposition cleaning of a husker”and the “flushing with unhulled rice.”An examination of the latter technique showed the Cs concentration in brown rice to be reduced by 90% from the early stages of husking. This result was not influenced by any initial contamination of the husker, and the resulting Cs concentration of the brown rice was below the regulation value. For this reason, we concluded that flushing rice huskers with unhulled rice is an easy and effective method for preventing radioactive cross-contamination. However, since the Cs concentration in the residue inside the husker after flushing tends to have a high Cs concentration, to prevent recurrence of crosscontamination it is necessary to remove the residue.

In paddy fields contaminated with radioactive substances and where planting is prohibited, high concentrations of radioactive substances have accumulated in the top 2 - 3 cm of the soil. The removal of topsoil is therefore a fast and reliable decontamination measure. However, it is difficult to control the removal thickness with commonly-used construction machines. This prompted us to develop a modified construction machine in which the removal thickness is more accurately controlled to ensure full decontamination. The first step in the method is to treat the thin surface soil with soil hardener, consisting mainly of MgO. The second step is to scrape off the thin surface soil by laterally moving the bucket of an excavator. The final step is to suck up the removed soil with a vacuum. This method allows for effective decontamination of radioactively contaminated topsoil with a smaller amount of soil removed.

Grassland renovation, including plowing and potassium fertilization is a major remediation technique that is applied to grassland contaminated with radionuclides released during the Tokyo Electric Power Company’s Fukushima Daiichi nuclear power plant accident. There are many public pastures on mountains in the Tohoku region (northeastern Honshu, Japan). Many of them are too steep for mechanical grassland renovation. A renovation method using a radio-controlled crawler tractor was developed for grasslands with steep slopes of 15 - 30̊. This tractor can also be used for mowing the grass on riverbeds. It can be operated up to 100 m away and automatically stops when it goes out of radio range. Together with Matsuyama Plow Mfg. Co., Ltd., we developed a rotary tiller for this tractor. As a result, a series of grassland renovation tasks, such as sweeping up contaminated vegetation, fertilization, tillage, sowing, and soil packing has been made safe by remote work in combination with a commercialized flail mower, a broadcaster whose spraying performance has been confirmed, and a prototype roller. The developed rotary tiller is able to closely track the ground surface, can finely cultivate the soil, and the tilling blades are highly durable, even in stony soil. In our experimental trials, the air dose rate of grassland decreased by 70% compared to before renovation. The resulting reduction factors for radioactive cesium concentration of harvested forage were in the range of 1.3 - 2.7 compared with no renovation. On stony grasslands, the working efficiency may be significantly lower due to stones becoming wedged between the blades. In practical grassland renovation of four steep grasslands, the average working efficiency was 4.05 hr/10a.

A review was conducted of the behavior of radioactive cesium in the aquatic system and its impact on agricultural-use water due to the accidental release of radioactive materials from the Fukushima Daiichi Nuclear Power Plant of the Tokyo Electric Power Company. The review includes analysis methods for low-concentration radioactive cesium in water, radiocesium sedimentation in irrigation canals, a real-time monitoring method for radiocesium in irrigation water, removal of radiocesium in water, and quantification of radiocesium flowing into paddy fields, carried by irrigation water.

The levels of radioactive cesium contamination in stored water and bottom sediment of irrigation ponds have been surveyed by governmental offices. They report radioactive cesium to have been detected in the water from a small number of ponds, and that,in some cases, radioactive cesium in the sediment significantly exceeded 8 kBq/kg. Experimental decontamination of the sediments and various research studies have revealed that radioactive cesium is mainly adsorbed on the surface layer of sediments and tends to bind strongly to clay particles and organic matter. In March 2014, the Ministry of the Environment announced the policy of carrying out decontamination of irrigation ponds. This was followed by rapid decontamination of ponds. In situ measurement technologies, such as the use of plastic scintillation fiber (PSF) and a pole sensors, have been developed that can find hot spots and count the vertical radioactivity distribution in sediment. The radioactive cesium concentration in sediments has been reliably decreased as a result of this decontamination project.

Four countermeasures have been adopted to reduce the contamination of brown rice by radiocesium released from the Tokyo Electric Power Company Holdings’ Fukushima Daiichi Nuclear Power Plant: 1) prohibition of rice cultivation and harvesting, 2) decontamination of farmland, 3) application of potassium and 4) inspection of brown rice. Since 2011, rice cultivation and harvesting has been prohibited in the evacuation-designated zones. In 2012, rice cultivation and harvesting was banned in areas where radiocesium-contaminated brown rice exceeded the present limit on radiation level of 100 Bq/kg. Decontamination of farmland has been conducted since 2012 by removal of topsoil in most cases. Additional potassium application has been recommended to raise soil exchangeable potassium content to 25 mg/100 g before conventional NPK fertilization. Since 2012, every 30-kg bag of brown rice produced in Fukushima Prefecture has been inspected to prevent shipment of any brown rice containing radiocesium exceeding the standard value from shipping. From 2020, sampling inspection is conducted except the evacuation ordered area.

Annual radiocesium monitoring was conducted from 2012 to 2019 after the accident at the Tokyo Electric Power Company (TEPCO)-Fukushima Daiichi Nuclear Power Plant (FDNPP). Radiocesium concentrations in farmland soils and crops were shown to have continuously decreased, and the morphological distribution of radiocesium in soil was also revealed. It also shown that extremely low amounts of radiocesium were transferred from the surrounding forests to agricultural land, and that the amount of radiocesium in paddy fields in mountainous areas decreased faster than would be predicted by radiocesium’s half-life. These studies are regarded as important information for determining whether crops with low radiocesium concentration can be produced. A method of evaluation of the abundance of dissolved radiocesium in the soil in forms that are easily taken up by plants has also been studied, and is expected to be used in farmlands that have resumed farming.

Uptake of K and Cs from roots is competitive, because Cs⁺ is absorbed by K transporters. Uptake of Cs by rice is mainly mediated by a high affinity K transporter, OsHAK1, in the roots. Under low soil-K conditions, Cs uptake is higher due to competition between K⁺ and Cs⁺. Increased expression of OsHAK1 in roots under low soil-K conditions also promotes the uptake of Cs. In the aboveground parts of the rice plant, Cs distribution changes dynamically after the heading stage. During the ripening process,cesium is translocated from the leaf blades and accumulates mostly in the uppermost internode. As yet, no Cesium transporters have been reported in the aboveground parts. The proportion of radiocesium accumulated in brown rice to that in the whole aboveground parts increases under low soil-K conditions. Sufficient K application is needed to prevent the accumulation of radiocesium in brown rice by regulating both the uptake from the roots and the rate of accumulation in the brown rice. Changes in available K and radiocesium in the soil should also be considered, because they vary with soil type and plant growth.

The accident at Tokyo Electric Company’s Fukushima Dai-ichi Nuclear Power Plant widely contaminated agricultural land in eastern Japan with radionuclides, particularly in parts of Fukushima Prefecture. The severe damage caused to agriculture and the environment remains of great concern in Fukushima. Because ¹³⁷Cs has a long half-life and is retained in the soil for extended periods, its transfer to crops is a long-term problem. Since the accident, NARO has been conducting research on the contamination of agricultural products and soils, and studies to establish strategies for reducing radiocesium transfer from the soil to crops. This review outlines the research results on countermeasures to mitigate radiocesium transfer from soil to upland crops.

The accident at the Tokyo Electric Power Company (TEPCO)’s Fukushima Daiichi Nuclear Power Plant in March 2011 caused radioactive substances to fall onto pastures and other areas. The National Agriculture and Food Research Organization (NARO), in cooperation with the relevant prefecture governments and public research institutes, have worked on the development of technologies to ensure the safety of animal feed. Renovation of grasslands with higher soil exchangeable potassium mass-fraction (30-40 mg-K ₂ O/100 g dry soil) has proved effective in reducing the concentration of radioactive cesium (RCs) in grass. It was shown that the cultivation of forage crops, such as corn and Italian ryegrass, in compliance with compost application standards, which had been practiced by farmers even before the accident, produces feeds with sufficiently low levels of RCs. This paper also describes other measures to reduce RCs the migration into forage rice and on the use of contaminated compost. Forage production, is based on many types of crops, and the production base varies from grassland, to farmland, to paddy fields, etc., in varying locations and with different soil conditions. Therefore, there are still some issues that have not been solved, and long-term efforts will be necessary in the future.

After the accident at Tokyo Electric Power Company’s Fukushima Dai-ichi nuclear power plant in 2011 caused radioactive cesium (RCs) to fall onto agricultural land, radioactive nuclide levels in some buckwheat (Fagopyrum esculentum Moench) grain subsequently exceeded the standard limits for radioactive materials, including that for RCs (100 Bq kg^-1). A survey of soil and buckwheat grain in farmers’fields and field experiments revealed soil-exchangeable potassium concentration to be significantly and negatively correlated with RCs concentration in the grain. Based on these results, farmers were recommended to establish a soil exchangeable K concentration of 30 mg 100 g^-1 in K₂O before applying basal fertilizer. After harvesting, grain from fields with lodged crops showed higher RCs than grain from fields with no lodging. In lodged plants, RCs in the grain was decreased by polishing. These results demonstrate that RCs of buckwheat grain from lodged plants can be decreased by removing soil from the grain surface by polishing and winnowing. Due to the countermeasures applied to decrease RCs in buckwheat grain since 2013,the standard limit for radioactive materials in buckwheat grain has been exceeded in only one sample that was detected in 2015. In 2014, buckwheat cultivation was resumed in physically decontaminated fields, from which radiation-contaminated surface soil had been removed, followed by soil dressing and plowing in areas where the evacuation order had been lifted. We have also been monitoring buckwheat cultivation by local farmers in decontaminated fields since 2015.

Radioactive materials such as cesium were released into the atmosphere due to the accident at Tokyo Electric Power Company’s Fukushima Daiichi Nuclear Power Plant following the Great East Japan Earthquake in March 2011. Fruit trees in the deciduous stage were contaminated on their surfaces, such as bark. Immediately after the accident, in collaboration with Fukushima Prefecture,we worked on elucidating the mechanism of radioactive cesium migration to fruits and developing decontamination technologies for radioactive cesium-contaminated orchards. Most of the radioactive cesium in the orchard soil remained in the surface layer of the soil. Since the roots of fruit trees are deeper than the radioactive cesium-retaining soil layer, radioactive cesium contamination of fruit trees was considered to be more influenced by transfer from the tree surfaces than from the soil. Therefore, removal of aboveground parts, such as by bark washing and pruning, is likely effective for reducing radioactive cesium. It was also suggested that the removal of bark as soon as possible after contamination was the most important, since the migration of cesium from the bark to the inside of the tree progressed with time after the accident. In the production process of half-dried persimmons, locally named ampogaki, continuous risk management from cultivation to shipment has been implemented by ensuring that only raw fruits with a low concentration of radioactive cesium are harvested, by controlling the processing process, and inspecting the product for radioactive cesium.

A decade has passed since the radioactive contamination of domestic agricultural, livestock and fishery products were caused by the accident at Tokyo Electric Power Company’s Fukushima Daiichi Nuclear Power Station. The major radionuclides contaminating domestic food products were radioactive iodine (¹³¹I) and radioactive cesium (¹³⁴Cs and ¹³⁷Cs). The Japanese government immediately set provisional regulation values for controlling the contamination level of these radioactive substances in food, and the inspection of radioactive substances in domestic food products was commenced. Due to these efforts, the contamination level of these radionuclides in food offered for sale, except for some natural foods, has been maintained at a low level since immediately after the accident. After the accident, consumer concern about the safety of radioactively-contaminated food grew rapidly. In response to this, since 2011, the results of radioactive cesium dynamics related to processing/cooking for domestic agricultural, livestock and fishery products have been actively acquired, primarily by domestic researchers. Here we review the government’s response to the radioactive contamination of foods immediately after the accident and outline the studies of the dynamics of radioactive cesium in the processing or cooking of domestic agricultural products.

On March 11, 2011, the Great East Japan Earthquake and subsequent tsunami damaged the Fukushima Daiichi Nuclear Power Plant (FDNPP). In response to information of FDNPP accident, measurement of the γ-ray nuclide concentration in cow’s milk was started at National Institute of Livestock and Grassland Science (NILGS: Tsukuba, Japan, 36^o02’N, 140^o12’E) from March 12, 2011. On March 15, the concentration of ¹³¹I in milk was 155.2 Bq/L and reached the highest value of 244.8 Bq/L on March 23. After that,it gradually decreased to the lower limit detection value on May 26, 2011. On the other hand, the concentration of radioactive cesium increased later than ¹³¹I. On March 15, the concentrations of ¹³⁴Cs and ¹³⁷Cs were detected at 1.87 Bq/L and 2.24 Bq/L, respectively,and the concentration did not increase significantly until March 20. On March 21, the total level of (¹³⁴Cs and ¹³⁷Cs) was detected above 10 Bq/L. and thereafter, maintained above 10 Bq/L for three months. On the other hand, the concentration of ⁹⁰Sr in milk did not increase after the FDNPP accident and was maintained at 10 - 30 mBq/L before the accident. The survey of radioactive cesium concentration in total mixed rations (TMR) at NILGS started in November 2011. The maximum ¹³⁷Cs and ¹³⁴Cs activities, 13.44 and 7.78 Bq/kg (dry weight), respectively, were measured in the TMR obtained on November 2012. The radioactive cesium concentration level decreased to about 0.2 Bq/L for raw milk and about 2 Bq/kg (dry matter) for TMR, and then remained flat.

In the evacuation zone of the Great East Japan Earthquake, there is an increasing risk of crop damage by wildlife during the resumption of agriculture due to a lower human presence. Although there are specific problems, such as the isolated nature of cultivated fields and depopulation of villages, the structure of increased risk is the same as that of the wildlife damage that is a growing problem nationwide. We therefore decided to adopt measures that are typically used nationwide. Electric fences, which are often selected in the evacuation area to prevent field intrusion, are inexpensive and highly effective, but they are often used in the wrong way and require significant maintenance. Wire mesh fences, however, although expensive to install, were concluded to be suitable for this area due to their lower maintenance requirements.

The nuclear power plant accident caused by the Great East Japan Earthquake spread radioactive materials widely around Fukushima. The interruption of farming caused by the evacuation of residents and the decontamination of farmland had a significant impact not only on cultivation, but also on the surrounding vegetation and management of weeds. This report briefly reviews the weed problems caused by the nuclear power plant accident that were investigated by the Tohoku Agricultural Research Center.

The Great East Japan Earthquake severely disrupted horticultural production in the Tohoku Pacific Ocean coastal region of Japan. In this paper, we describe reconstruction support for strawberry production in Miyagi Prefecture that was damaged by the disaster. We have been involved in supporting horticultural reconstruction efforts in this region since the earthquake struck in 2011. The Japanese government began a research project in 2012 to support reconstruction of the affected agricultural area (“A Scheme to Revitalize Agriculture and Fisheries in Disaster Areas through Deploying Highly Advanced Technology”). The horticultural research station for the project, located in Yamamoto Town (Miyagi Prefecture), is a Venlo-type greenhouse 7200 m² in area. Yamamoto Town and nearby Watari Town together comprise a major strawberry-producing region. Technical support for reconstructing the strawberry greenhouse facilities was therefore a high priority of the research project. Since the inception of the project, we have provided technical information to growers and the local extension service, and we have worked with them to solve technical problems. Due to the amount of salt accumulated in the soil after it was flooded by the tsunami that followed the earthquake, we determined that an elevated growing-bed system was the best option for restarting strawberry production. We designed and proposed an elevated growing-bed system consisting of individual growing containers and a crown-temperature control system. Our aim was to help prevent the spread of soil-borne plant diseases that tend to occur in long beds. Separate containers also provide the drainage needed to keep the root zone (air and water contents) optimal for growing strawberries. The crown-temperature control system, established by the National Agriculture Research Organization (NARO), was added to increase yield and reduce heating costs. Large-scale, multi-span greenhouses were constructed by the local government (total 152 growers, 41 ha) and the first strawberry cultivation restarted in September 2013. In the research station greenhouse, we have been continuously demonstrating and developing new technologies and providing information to strawberry growers.

Many horticultural structures, such as high tunnels and greenhouses along the Pacific Coast of the Tohoku and Kanto areas were crushed by the tsunami that followed the 2011 Tohoku Earthquake. The National Agricultural and Food Research Organization (NARO) investigated damage caused to horticultural structures by the tsunami and seismic motion. The purpose of this review is to report on the damage caused to horticultural structures and incidental facilities by the earthquake, and consider responses to future similar disasters. Major economic impacts by the tsunami included agricultural facilities, horticultural structures, agricultural machines and agricultural equipment. The horticultural structures typically seen damaged were as follows: (1) inshore greenhouses washed away by the tsunami, (2) slight damage to greenhouse structures distant from the shore, (3) earthquake damage to some environmental control systems, high bench cultivation systems and glass roofs and walls of multi-span greenhouses, (4) decreased production due to environmental control systems (ventilators, thermal curtains, heaters, etc.) and irrigation systems having stopped due to power failure. Earthquakes, typhoons and heavy snowfall frequently occur in Japan, making reinforcement of greenhouse structures necessary. There is a need for development of renewable energy sources that can power environmental control technology during mains power failures and suspension of water supplies.

In the Hamadori area of Fukushima Prefecture, which was affected by the earthquake, tsunami, and nuclear disaster, we carried out an advanced technology demonstration project for cut flowers. Being isolated from the external environment, the products are less subject to consumers’misgivings. We have developed new efficient and labor-saving technologies that enable year-round production of Eustoma (Lisianthus). NFT (nutrient film technique) hydroponic cultivation and its disease control techniques enable rapid and uniform seedling production using a closed seedling-raising device. The use of a photosynthesis model specific to the Eustoma that achieves greenhouse management at the skilled producer level. There is a sophisticated central environmental control system, a ducted pad and fan system that can separately control temperature and humidity, and a coloring accelerator that enables harvesting of cut flowers in the bud state. Combining these techniques has made it possible to cultivate three crops a year with unconstrained sowing times, which is an improvement over the single-yearly crop that was previously grown. We designed and demonstrated a year-round cultivation system that spreads out shipping times by cultivation in multiple greenhouses that have installed this technology. This system is anticipated to be adopted by new players. Specialized technologies are also anticipated to be applied to conventional soil cultivation.

The design strength of a greenhouse constructed using scaffold materials was analyzed by three-dimensional structural analysis under required wind and snow loads. The greenhouse was built on an empirical research site along the southern coast of Iwate Prefecture and published as a construction manual, In addition, we calculated three strengthened models to provide a reinforced structure that is capable of withstanding heavier snowfall. The original model of the greenhouse structure was resistant to a snow load of 40 cm in depth as well as a wind load of 35 m/s. However, under a snow load of 67 cm in depth, even when no structural member of the greenhouse exceeded the allowable bending stress, the original model needed an additional supporting structure. This was because the deflection of the rafter significantly exceeded the guideline for deformation. The strengthened models that added post, beam, and strut support to the rafter into the original structure without an interior column successfully suppressed the deformation of the rafter. However, under a snow load of 75 cm in depth, a particular part of the connection member subject to excess bending might be damaged. The reinforcement employing the interior column to the structure,even when the column span is widened from 1.8 m to 2.0 m,may have still greater endurance to a heavy snow area.

Since the Great East Japan Earthquake in 2011, the production and sales of cucumber, the main vegetable product in coastal southern Iwate, have decreased, thereby requiring the development of technology for the reconstruction of this region. As this region has few snowfall days and a relatively long sunshine duration in winter, using multi-layered thermal curtains (insulation curtains) as the inner covering material of greenhouses could be effective to save fuel consumption and increase the farmers’profit. However, the optimal opening/closing timings tendency of the different insulation curtains to minimize fuel consumption remain unknown. This study presents a simplified model to calculate fuel consumption using heat balance and transfer equations and applies the model to combinations of greenhouse orientation and insulation curtain type to identify optimum opening/closing timings. Results show that (1) daily fuel consumption fluctuations could be captured, while heating start and end times tended to be earlier and later, respectively, than measured values; (2) the opening and closing timings for insulation curtains made of materials with a high heat transmission coefficient tended to be early and delayed, respectively; and (3) the opposite tendency was observed for insulation curtains made of materials with a high solar transmittance. The findings of this study are expected to contribute to energy savings by minimizing the heating fuel consumption needed for vegetable production in this region.

In the disaster-affected area of Fukushima, farming on consolidated rice paddy fields and protected horticulture areas has recommenced. This is in order to prevent the risk of harmful rumors. The farmers commute from a far distant refuge since the evacuation order has been lifted. In addition, their greenhouses and arable lands are often scattered. This has made it difficult for them to visit their production sites frequently, although some farmers have started to plant new cash crops as farming has restarted. In order to manage this situation, it would be helpful for such farmers to obtain agricultural information without physically visiting the farmland. This would require an inexpensive remote monitoring system which could be easily introduced and adapted according to the farmer’s needs, to provide agricultural information or cultivation history. Commercially available remote monitoring systems are designed to be used throughout the year and are relatively expensive for short-term use, such as during the seedling growth period. Therefore, we devised a remote monitoring system named the “Kayoinougyo Shien system”after the word “Kayoinougyo”that the farmers who commute from their place of refuge or residences far from their farms to the area where farming has restarted. The new technology is based on a commercial IoT prototyping kit with Web API and a messaging application. We demonstrated its capability and usefulness in the greenhouse in the regenerated area of farming in Fukushima. In this study, we evaluated the practicality and effectiveness of the system by adding the functions of data statistics and graphic data notification, and providing data on temperature, humidity, soil moisture content, and photographs taken by IoT camera, to meet the needs of the farmers. The accuracy of the temperature sensor was within ± 1 °C. The error rate of the data notification was less than 1% during the test period. The farmers were able to determine what needed to be done; whether to open the windows of their greenhouses or not, or irrigate their crops, by obtaining data at the required intervals and utilizing it in cultivation. Therefore, we were able to confirm the practicality and effectiveness of this system.