We analyzed the effects of hummocky microrelief on soil organic carbon (SOC) stocks of permafrost-affected soils (or Gelisols) in northern Canada. We compared the microrelief and SOC stocks in black spruce forests on clayey and sandy sediments in Mackenzie upland area. Hummock formation was maximal in clayey soils at the middle position of upland with a shallow permafrost table, where the soils were seasonally flooded by spring snowmelt and summer permafrost thawing. The higher water content due to poorer drainage, rolling permafrost table, and freeze-thaw cycles can promote greater hummock formation in the clayey soils. The soils on the strongly-developed hummocky microrelief have greater SOC stocks than those on weakly-developed microrelief. This can be explained by the retardation of microbial decomposition by summer flooding and accumulation of recalcitrant lichen and moss litters on strongly-developed hummocky microrelief. The concentration of oxalate-extractable short-range-order iron oxides in soils, which are enriched through redox cycles by seasonal flooding, can serve as a rough proxy for predicting local variation in SOC stocks in the mineral soils in black spruce forests on permafrost.

　　Fluvial terraces of different formation ages are in Tokachi region, Hokkaido. Fluvial terraces are classified as high terrace, middle terrace and low terrace as topographic classifications. In high terrace, Andosols was generated from parent material, which was Holocene volcanic ash and Late Pleistocene volcanic ash on diluvial formations. Geomorphic development by erosion and deficiency of tephra were conceded in high terrace. Wet type Andosols (HT-1 and HT-2 respectively) were distributed in this high terrace. The depth of groundwater influence in Andsols of HT-1 and HT-2 was different by effect of micro-topography. In middle terrace, Andosols was generated from parent material which was Holocene volcanic ash and Late Pleistocene volcanic ash. Dry and wet types Andosols (MT-1 and MT-2 respectively) were distributed by effect of habitat as well as in high terrace. Andosols in low terrace (LT) was generated from parent material, which was Holocene volcanic ash on fluvial deposit. In low land that was formed most newly, Alluvial soil (LL) was generated from fluvial deposits. Wet type Andosols (HT-1, HT-2 and MT-1) distributing at high and low terraces were observed iron mottle at a depth of >50 cm. Therefore soil order could not be reflected that HT-2 and MT-1 was wet condition, by the Agricultural Soil Classification and Unified Soil Classification System of Japan. On the other hand, in the Japanese soil classification (2017), only HT-1 was classified as Wet type Andosols. Wet condition by snowmelt in early spring affects crop production in cool temperate area like Hokkaido. As a result, distinction of wet type soil and dry type soil is important. Our study suggested that is necessary to rethink criteria of wet condition to Andosols subgroup of Japanese soil classification (2017).

　　Surface-soil carbon concentrations can be estimated from satellite and drone images. As other soil factors related to soil carbon concentrations may be evaluated in the same way as surface-soil carbon concentrations, they too should be estimable from remotely sensed data. To this end, we investigated the relationship between measured surface-soil carbon concentrations and phosphate absorption coefficients (PACs) affecting phosphate fertilization in volcanic acid soil areas of the Tokachi region, Hokkaido. Surface-soil carbon concentrations can explain 51% of the regional variability of PACs observed in soils composed solely of volcanic ash, and 70% of that in soils comprising volcanic ash and diluvial or alluvial deposits. In an upland field with soils containing volcanic ash and diluvial deposits, surface-soil carbon concentrations can explain 91% of PAC variations.