Tomotsugu Yazaki

Soil Frost Control: Its Application to Volunteer Potato Management in a Cold Region

The earlier onset of persistent snowcover since the late 1980s has narrowed the time window for soil-surface cooling without insulating snowcover, drastically reducing the soil frost depth in eastern Hokkaido, Japan. In crop fields managed by rotation, small potato tubers left unharvested in the fall survive the winter and emerge as weeds during spring–summer (volunteer potatoes). To eliminate them, soil frost depths are manipulated by artificially controlling snowcover thickness, guided by numerical soil-temperature model prediction. Field trials demonstrated that soil frost depths were predicted within accuracy of several centimeters. The optimal soil frost depth of 0.3–0.4 m is proposed as a compromise between the elimination of volunteer potatoes and permissible soil frost depth to prevent negative effects on agriculture in the following spring. The numerical model also facilitates decision-making related to the work schedule of snow plowing practices (yukiwari in Japanese). This method is adopted by local potato producers, who manage farmland on a large scale. This method represents a new agricultural technology that is useful for adaptation to climate change.

Effects of saturated hydraulic conductivity on volunteer potato (Solanum tuberosum L.) tuber survival

Abstract In situ observations were conducted at eight fields in the Tokachi region of the northernmost island of Japan to assess the effects of soil physical conditions on the survival of volunteer potato (Solanum tuberosum L.) tubers. Statistical analyses revealed a positive correlation between the survival rate and the lowest value of saturated hydraulic conductivity to a depth of 0.5 m, except for data from one field where potato tubers were killed by low temperatures below –3°C during winter and from another field with poor drainage despite high soil permeability to 0.5 m in depth. Incubation experiments indicated that potato tubers survived in saturated soil at 0 and 6°C, which respectively matched soil temperatures during the snowmelt period and 1 week thereafter. This result suggests that potato tubers can survive prolonged exposure to moist surface soil caused by large amounts of snowmelt water during the spring snowmelt period. The incubation experiment results also indicated that potato tubers were killed in saturated soil at 15°C. This temperature was almost equal to the average air temperature during the period when volunteer potato tubers were sprouting in the field. Therefore, this result implies that the potato tubers will be killed after a substantial amount of rainfall during the subsequent warm period at poorly drained fields.

Water and nitrate movements in an agricultural field with different soil frost depths: field experiments and numerical simulation

Abstract To evaluate water and anion movement in an agricultural field in different frost conditions, a paired-plot field experiment was conducted at an agricultural site in northern Japan where a significant decrease in the frost depth has occurred during the past 20 years. Snow cover was removed to enhance soil freezing in one plot (treated plot), whereas natural conditions were maintained in a control plot. The maximum frost depth was 0.43 m in the treated plot and 0.11 m in the control plot, which induced substantial differences in water movement throughout the winter. A substantial amount of water moved upward before the onset of snowmelt. However, nitrate did not move markedly before the snowmelt period in either plot. The amount of snowmelt infiltration in the control plot was larger than in the treated plot. Correspondingly, the peak of nitrate content in the control plot was deeper than that in the treated plot after the snowmelt period. Soil freezing, snow accumulation and snowmelt processes were simulated reasonably well using a one-dimensional numerical model: Simultaneous Heat and Water (SHAW). Nevertheless, the model performed poorly for simulating soil thawing and soil water movement, suggesting a need for improvement.

Winter Nocturnal Air Temperature Distribution for a Mesoscale Plain of a Snow-Covered Region: Field Meteorological Observations and Numerical Simulations

AbstractWinter air temperatures strongly affect crop overwintering and cold resource usage. To clarify how winter air temperature distributions are formed in a mesoscale plain, field observations and simulations were conducted for the Tokachi region in Japan. Results elucidating the winter climate within the plain revealed that the winter mean air temperature at each site was correlated closely with the mean daily minimum air temperature. The daily minimum air temperature was not correlated with altitude, suggesting that local variation of the daily minimum temperature influences the temperature distribution. Observations at different distances from the upwind mountains revealed that nocturnal air temperatures were higher for stronger winds closer to the mountain foot. Low temperatures associated with wind speed suggest that radiative cooling strongly affects the temperature distribution. Wind and temperature conditions in the boundary layer influence the degree of drop in nocturnal air temperature and it...