2019 年 63 巻 2 号 p. 61-72
An understanding of the differences in yield potential and soil characteristics between slope directions in hilly uplands fields is fundamentally important for efficient management of the fields. Although the influences of slope direction on soil organic matter have not been widely studied in arable land, there are extensive reports in native or uncultivated land covered with forest. The present study was done in hilly upland potato fields in Kamikawa district, Hokkaido, Japan to evaluate differences in yield potential and soil characteristics between slope directions. Eighty paired surface soil and potato samples were collected at flowering and harvesting stages, respectively, over a period of two years. Slope direction of each field was determined using ArcGIS software, and potato fields were categorized into two groups (north-facing and south-facing) based on slope direction. This study revealed that (1) the average soil total carbon content was significantly higher in fields with north-facing slopes (18.5 g kg-1) compared to south-facing fields (13.9 g kg-1), (2) cation exchange capacity was also significantly higher in north-facing compared to south-facing fields, and (3) tuber yields of Toyoshiro cultivar were relatively higher in fields with slope direction facing south than those facing north whereas Kitahime cultivar showed the opposite trend. In conclusion, depending on the cultivar, slope direction can affect potential yield by altering climate conditions (air temperature, soil temperature, day length, and diurnal variation of temperature) as well as by modifying soil characteristics.
