Controlling the depth of soil frost in farm fields in Japan

Winter climate change has resulted in earlier onset of deep snow cover and reduced soil-frost depth in eastern Hokkaido, Japan, since the late 1980s. In the Tokachi region, a major potato-producing area of Japan where upland fields are managed by rotation, small potato tubers unharvested in the fall survive the winter and emerge as weeds (volunteer potatoes) during the next crop season and cause problems for producers. This is attributable to the thermal insulation of soil by the thick snowpack and inhibits unharvested potato tubers from freezing to die. To develop an adaptive countermeasure for these problems, a soil-frost depth control technique, which manipulates snow cover thickness and controls soil-frost depth to eliminate volunteer potatoes, was developed. Field trials demonstrated that soil-frost depths can be predicted with an accuracy of several centimeters. A target soil-frost depth of 0.30 m is proposed for complete elimination of volunteer potatoes. A numerical model facilitates decision-making related to the scheduling of snow-plowing practices for freeze death of potato tubers. This method has been adopted by local potato producers who manage farmland on a large scale. It represents a new agricultural technology that is useful for adaptation to climate change.