Soil moisture was observed in situ for three years (1992-1994) to compare the effect of different vegetations (forest, grassland and wheat field) on soil moisture under the same meteorological conditions. The observation sites were located in a boreal humid climate where snow covers for about four months annually. The soil moisture was measured by the heat-probe method (Kasubuchi, 1992). It could measure the soil moisture automatically and continuously even under the snow covered condition. Seasonal variations of the soil moisture was characterized into three stages; from thawing to active vegetation (spring to summer), rainy (autumn) and snow covered (winter) period. The soil moisture and temperature were much influenced by the active time and the root system of each vegetation. Differences in soil moisture among the years depended on the meteorological conditions which affected the vegetation growth. From these observations, it became clear that the soil moisture and the soil temperature were affected not only by meteorological conditions but also by the vegetations.
A dramatic reduction in soil frost depth has been reported for Hokkaido Island of northern Japan over the last 20 years. Since soil frost strongly affects snowmelt infiltration and runoff, the reduction in frost depth may have altered the water and nutrient cycles in this region. A paired‐plot experiment was conducted in an agricultural field in Tokachi, Hokkaido, to compare the movement of soil water at different frost depths, controlled by manipulating the depth of snow cover. Snow was removed to enhance soil freezing in the treatment plot and was undisturbed in the control plot. The soil froze to a maximum depth of 0.43 m under the treatment plot and 0.11 m under the control plot. During the freezing period, the amount of upward soil water flux toward the freezing front in the treatment plot was more than double that in the control plot. During the snowmelt period, infiltration of meltwater was unimpeded by the thin frozen layer in the control plot, whereas the relatively thick frozen layer in the treatment plot impeded infiltration and generated 63 mm of runoff. These results clearly show that the changes in the timing and thickness of snow cover deposition can cause a dramatic reduction of frost depth and change in the soil water dynamics.
Emergence of unharvested potatoes that survived during winter becomes source for nematodes and diseases, causing serious weed problems in rotational crop fields. Herein, we describe frost killing of unharvested potatoes in potato–wheat rotation fields using snow compaction ‘yuki-fumi’ under multiple climate conditions. The effect of snow compaction in controlling volunteer potato over winter wheat was verified in 17 farm fields in Hokkaido, Japan from 2015–16 to 2017–18. A reduction in the temperature of soil under ‘yuki-fumi’ was slower than that under snow removal ‘yuki-wari’, which was used in previous studies. However, snow compaction achieved a substantial reduction in volunteer potato sprouting in most of the experimental sites. The sprouting of volunteer potatoes was reduced in snow-compaction blocks with soil temperatures below −3°C. For winter wheat sowing in potato–wheat rotation, the soil is tilled to a shallower depth than that for other crops, and thus, unharvested potato tubers are not pushed down during field preparation for wheat sowing. Consequently, even if the soil temperature drops slightly, snow compaction can regulate the sprouting of volunteer potatoes. Snow compaction did not exert any apparent influence on wheat growth and grain yield. At some sites with a deeper snowpack, development of soil frost and reduction in soil temperature did not progress with continued snow compaction owing to fallen snow. We validated the usefulness of snow compaction as a countermeasure to control volunteer potatoes in snowy regions.
The force‐restore method (FRM) was originally developed for estimating diurnal fluctuations in the ground surface temperature. Because of its relatively simple parameterization, it is commonly applied in meteorological and other models for this purpose. Its application to the calculation of deeper soil temperatures, to frozen soils, and to soils under snow covers has heretofore not been possible. This study demonstrates an extension of the FRM that permits accurate estimates of seasonal variation in mean daily deep soil temperature. The extended FRM is shown to provide a lower boundary condition for the heat conduction method, permitting a combination of the two approaches that avoids some limitations of each. The combined approach provides representations of the mean daily soil temperature, soil temperature at depth in frozen soils, and ground surface temperature under a snow cover. Diurnal variations can also be calculated. The extended method and combined approaches are tested using field site measurements collected in cold weather periods in Saskatchewan, Canada, and are found to provide a reasonable representation of measurements.
Appropriate growth forms for strawberry production in a plant factory with artificial lighting (PFAL), which is a recently developed production system, remain undetermined. Improving strawberry productivity in a PFAL requires insights into the interplay between production characteristics (growth and photosynthesis) and growth forms, such as plant height and leaf area ( LA ), which are major determinants of crop yield. Growth status, yield, and photosynthetic characteristics of the two cultivars of strawberries ( Fragaria × ananassa Duch. Tochiotome and Koiminori) with different growth forms were examined. ‘Koiminori’ exhibited a 1.9-fold higher yield and a 2.0-fold greater total dry weight of respective organs compared with ‘Tochiotome’. The single-plant photosynthetic rate ( A P ), serving as an index for both cultivars, was 2.2-times higher for Koiminori than for Tochiotome. The photosynthetic rates of a single leaf ( A L ) and LA were also analyzed as important factors that influence the A P . The A L for ‘Koiminori’ surpassed that of ‘Tochiotome’ by 1.4 times. This was attributed to the elevated photosynthetic photon flux density received by the upper leaves of Koiminori, which is a consequence of its higher plant height in proximity to the light source. Evaluation of four photosynthetic capacities, maximum rate of carboxylation, maximum rate of electron transport, photosynthetic rate under saturating light, and light utilization efficiency, which are potential factors that affect A L , revealed no differences in these capacities between cultivars. ‘Koiminori’ exhibited a significantly larger LA (2.3- to 3.1-times) than ‘Tochiotome’, indicating that the former’s higher A P resulted mainly from its higher A L and larger LA . Thus, strawberry production in a PFAL can be improved by growing cultivars with growth forms such as higher plant height and larger LA .
