Planned snow compaction approach (yuki-fumi) contributes toward balancing wheat yield and the frost-kill of unharvested potato tubers

Snow compaction implements the thermal conditions compatible with both killing volunteer potatoes and good wheat growth. To reveal how soil freezing regulates volunteer potatoes without preventing the growth of winter wheat, we conducted experiments in a wheat field in Hokkaido, Japan (42°53′N, 143°05′E), from winter 2013 to summer 2017. Owing to the enhanced thermal conductivity of snowpack during cold periods, different timings and frequencies of snow compaction allowed us to target different soil temperatures and frost depths. In most years and blocks, snow compaction achieved soil frost depth >0.3 m and killed all potato tubers, but in 2016–17, soil frost depth was <0.3 m in DC, and 7% of potatoes sprouted. These findings indicate that snow compaction before a heavy snowpack can effectively kill tubers. Wheat grain yield did not differ among treatments except in 2013–14. Deep soil freezing did not always reduce the wheat yield, but delayed snowmelt and thus delayed growth enhanced the likelihood of plants experiencing higher air temperature at the early spike development stage. Although changes in yield components such as culm length and spikelet density were associated with varietal responses to temperature, warm conditions in 2014 reduced the dry matter and shortened the grain-filling period, resulting in a greater decrease in yield. Furthermore, rapid hard freezing and direct physical impact may have caused much greater injury to wheat under a shallow snowpack in 2013–14. Thus, our findings indicate that proper snow compaction can balance wheat production and kill unharvested potatoes in crop rotation, and except for hot summer, gentle procedure of grain-filling could compensate the grain weight even in less spring growth.