※日本の森林土の表層1ｍ内の有機炭素量は４５.７億トン
『Abstract
An accurate estimate of the organic carbon stock in the soil
in a country allows the global estimate to be refined. This study
estimated the organic carbon stock in forest soil in Japan using
available data.
Forest soil was classified into 15 soil units, and the extent
of each soil unit was determined using digital soil and land use
data. A representative value of the organic carbon density for
each unit was determined from 3391 soil profiles obtained in a
nationwide soil survey.
The mean organic carbon density of the forest soils differed
in each soil unit; the density to a depth of 1 m ranged from 33.0
kg m-2 for Black soils (Andisols) to 8.2 kg m-2
for Immature soils (Regosols). The variation within soil units
was also large, and the coefficient of variation was almost 40％.
The area-weighted average organic carbon density was 9.0 kg m-2
in the first 30 cm of soil, and 18.8 kg m-2 in the
upper 1 m. The estimated total organic carbon stock in the forest
soils of Japan was 4570±500 Tg (1 Tg = 1012
g) in the first 1 m (±95％ confidence limit), excluding
carbon held in the surface organic horizons and buried horizons.
The Brown forest soil group (mostly Cambisols) made the largest
contribution, with over 3000 Tg . Forty-eight percent of the total
organic carbon stock (2180 Tg C) was contained in the top 30 cm.
The contribution of the surface layers to the organic carbon was
clear.
The wide variation in organic carbon density by soil type and
the high density of organic carbon on a national scale in Japan
is related to the distribution of volcanic ejecta. The concentration
of organic carbon in the surface layers implies that soil conservation
is important both to maintain land productivity and to counter
global warming.
The analysis of variability in the organic carbon density with
soil type demonstrated that estimation methods should be improved.
Keywords: Forest soil; National soil classification; Organic carbon
density; Organic carbon stock; Japan』
1. Introduction
2. Materials and methods
2.1. Soil grouping and areal extent
2.1.1. Soil units
2.1.2. Areal extent
『
|
Table 1 Categories of soil units used in this study and their
area （本研究で使われる土壌単位のカテゴリーと面積） |
|||||
| Soil unit | Name of soil unit | Original soil group | Soil group, subgroup, type and subtype | Soil Group |
(km-2) |
| References cited | Economic Planning Agency (1967) | Forest Soil Division (1976) | FAO, ISRIC, and ISSS (1998) | ||
| Dry PZ | Dry podzolic soils | Podzols [1 map unit] | Dry podzolic soils subgroup [3 soil types] | Podzols | 5752 |
| Wet PZ | Wet podzolic soils | Podzols [1] | Wet humus podzolic soils subgroup [3], Wet iron podzolic soils subgroup [3] | Podzols | 4151 |
| Dry BFS | Brown forest soils (dry type) | Brown forest soils [1] | Dry bfs (loose granular structure type), Dry bfs (granular, nutty structure type), Weakly dried bfs | Cambisols, Andosols | 28,919 |
| Moist BFS | Brown forest soils(moist type) | Brown forest soils [1] | Moderately moist bfs, Moderately moist bfs (drier subtype) | Cambisols, Andosols | 10,271 |
| Wet BFS | Brown forest soils (wet type) | Brown forest soils [1] | Slightly wetted bfs, Wet bfs | Cambisols, Andosols | 4490 |
| d BFS | Dark Brown forest soils | Brown forest soils [1] | Dark bfs subgroup [3] | Cambisols | 4383 |
| ry BFS | Reddish and Yellowish Brown forest soils | Brown forest soils [5] | Reddish bfs subgroup [5], Yellowish bfs subgroup [6] | Cambisols | 24,238 |
| g BFS | Surface gleyed Brown forest soils | Brown forest soils [1] | Surface gleyed bfs subgroup [5] | Cambisols | # |
| RY | Red and Yellow soils | Red and yellow soils [3] | Red soils [5], Yellow soils [6], Surface gleyed red and yellow soils [4] | Acrisols, Alisols, Cambisols | 4610 |
| BL | Black soils | Black soils [6] | Black soils subgroup [6] | Andosols | 24,550 |
| l BL | Light-colored Black soils | Black soils [2] | Light colored black soils subgroup [6] | Andosols | 7753 |
| DR | Dark red soils | Red and yellow soils [1] | Dark red soils group [18] | Cambisols, Luvisols | 491 |
| GL | Gley soils | Gley soils [3] | Gley soils group [3] | Gleysols | 4067 |
| PT | Peaty soils | Peaty soils [3] | Peaty soils group [3] | Histosols | 74 |
| IM | Immature soils | Immature soils [8], Debris soils [2], Rock outcrop [1] | Immature soils group [2] | Regosols, Arenosols, Fluvisols, Leptosols | 18,523 |
| bfs, Brown forest soils; #, area of surface gleyed bfs is included in that of dark bfs. | |||||
2.2. Profile data set
2.2.1. Method of soil analysis
2.2.1.1. Organic carbon
2.2.1.2. Dry bulk density
2.3. Organic carbon stock
2.3.1. Individual (profile-by-profile) organic carbon density
2.3.2. Data variation and probability of the estimate
3. Results and discussion
3.1. Area by soil unit
3.2. Dry bulk density
3.3. Organic carbon density
3.4. Organic carbon stock
『
|
Table 5 Mean soil organic stock of forest soils in Japan by
soil unit （日本の土壌単位ごとの森林土の平均土壌有機炭素含量） |
||
| Soil unit | 0-30 cm | 0-100 cm |
|
|
||
| Dry PZ（乾燥ポドゾル） | 58 | 100 |
| Wet PZ（湿潤ポドゾル） | 47 | 94a |
| Dry BFS（乾燥褐色森林土） | 228 | 497 |
| Moist BFS（半湿褐色森林土） | 1010 | 2149 |
| Wet BFS（湿潤褐色森林土） | 40 | 99 |
| d BFS（暗褐色森林土） | 42 | 63a |
| ry BFS（赤黄褐色森林土） | 179 | 278 |
| RY（赤黄色土） | 31 | 61a |
| BL（黒色土） | 340 | 810 |
| l BL（明黒色土） | 82 | 139a |
| DR（暗赤色土） | 4 | 8a |
| GL（グライ土） | 37 | 77a |
| PT（泥炭土） | 13 | 26a |
| IM（未成熟土） | 73 | 152 |
|
See Table 1 for the definitions of the soil uit codes. aThe mean value for 0-70 cm was used for the estimation. |
||
4. Conclusion
Acknowledgements
Appendix A. Source of the soil profile dataset used in this study
A.1. Reports of soil survey projects
A.2. Additional publications
References