2021 Volume 2021 Issue 8 Pages 35-41
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.
