Climate change impacts
In the Tokachi and Okhotsk districts of Hokkaido, the soil becomes frozen in the winter due to severe cold and low snow cover. When this reaches deeper soil this causes freeze damage and death for potatoes that have not been harvested. However, in recent years, snow cover has increased in early winter, and soil freezing (see Note 1) has become shallower due to the insulating effect of snow. As a result, the issue of potatoes not freezing, turning into weeds the following year and then becoming "stray potatoes" has become a serious problem. As weeds, stray potato plants use up fertilizer and inhibit crop growth after rotation (see Note 2). They are also a source of contamination by hosting pests and mixing with other potato varieties.
(Note 1) Soil freezing is a phenomenon in which moisture contained in soil freezes. It only occurs when the daily average temperature falls below 0℃ and the snow depth is under 20cm. Source: Hokkaido Kushiro General Promotion Bureau website
(Note 2) In order to maintain soil integrity, different types of crops are cultivated on the same land in a fixed order which is repeated. Source: NAROPEDIA, National Agriculture and Food Research Organization (NARO)
Adaptation activity
The National Agriculture and Food Research Organization (NARO) has previously demonstrated that creating snow breaks (Fig. 1), where snow is removed from alternating strips of land, can effectively prevent the overwintering of potatoes. The strips of snow-free soil freeze, causing stray potato plants to die off. Compared to having to the manually extract stray plants, the use of snow breaks is significantly less labor intensive.
However, if soil becomes too deeply frozen, snow melt-water will not penetrate. This has implications for the issue of stray potato plants and productivity, and the environment generally. That is to say, 1) the spring thaw, and therefore farming work, may be delayed and 2) greenhouse gas emissions from the soil may increase in early spring. The Hokkaido Agricultural Research Center, NARO therefore suggests that by limiting the depth to which the land freezes to about 30cm (between the range of 28 to 33cm), stray potato plants can be eradicated and also nitrate pollution caused by runoff from leftover fertilizer can be reduced (Fig. 2).
Outputs / Expected benefits
Soil freezing has resulted in significant labor savings and is a sustainable countermeasure against stray potato plants.
In addition, limiting the depth of soil freezing by using snow breaks increases winter productivity by conserving labor costs and fuel consumption. In addition, greenhouse gas emissions can be cut by keeping nitrates in cultivated land, this not only contributes to environmental conservation, but also enhances productivity in cold regions through maintaining soil fertility and increasing crop yields.
