113

Environmental and Agricultural Significanceof Volcanic Ash Soils
Sadao SHOJI1 and Tadashi TAKAHASHI 2*
1

Professor Emeritus, Tohoku University
5-13-27, Nishitaga, Taihaku-ku, Sendai, 982-0034 Japan
2
Graduate School of Agricultural Science, Tohoku University
1-1, Tsutsumidori, Amamiya-machi, Aoba-ku, Sendai, 981-8555 Japane-mail: tadashi@bios.tohoku.ac.jp*corresponding author

Abstract
Volcanic ash soils begin to form with rapid restoration of vegetation soon after ash deposition andcreate a productive and comfortable environment. They also have various important functions such as
accumulation of large amounts of organic carbon and nitrogen, plentiful storage of water, water quality
improvement, and preservation of paleoenvironment and archaeological artifacts. Volcanic ash soils
are among the most productive soils in the world. Nowadays they are most extensively utilized for
growing high-value horticultural crops in Japan. The properties relating to their soil productivity arecomprehensively described. In order to solve the serious problems caused by unsuitable management
and to sustain volcanic ash soils, crop rotation, soil improvement, and precision agriculture and programmed fertilization are encouraged. Recommended rotations for with high economic advantages
also include crops to control soil-borne diseases and nematodes, gramineous plants to enhance soilorganic matter levels and crops having symbiotic interactions with arbuscular mycorrhiza that promote
plant uptake of soil phosphorus. Some volcanic ash soils have soil horizons that strongly inhibit plantroot development. Soil improvements such as deep cultivation and soil mixing are practiced for such
soils. Programmed fertilization using controlled-release fertilizers with high performance is recommended especially for intensive agriculture on small-scale fields. Correctly programmed fertilization
can be conducted at the best site by single basal application for most crops in Japan. With proper
management volcanic ash soils are capable of high productivity and long-term agricultural and environmental sustainability.
Key words: crop rotations, functions of volcanic ash soils, programmed fertilization using CRFs,
soil rejuvenation, sustaining volcanic ash soils

1. Significance as the Soil Environment
Though volcanic eruptions are highly destructive,
this natural phenomenon is beneficial in the long term.
Rapid restoration of vegetation and soil environment
takes place on volcanic ash deposits soon after the ash
deposition event. The periodic additions of volcanic
ash generally improve the soil physical and chemical
properties and renew the soil productivity. Volcanic
ash soils provide a comfortable living environmentand create a favorable landscape for recreation andhuman health. They also accumulate a large amountof organic carbon and nitrogen as important components of soil organic matter that are the main sourcesof nitrogen for plants, and various nutrients andenergy for soil organisms. The accumulation of car-bon is helpful in sequestration of atmospheric carbon
dioxide, the most important greenhouse gas. Volcanic ash soils with well developed soil structures canhold a large amount of plant-available water and candecrease flood waters. Volcanic ash soils generally
have sedentary multi-storied profiles and resist soil
disturbance, truncation and displacement due to natural and human activities. They preserve highly useful information such as on paleosoil environments andpaleovegetation, and archaeological remains and artifacts.
1.1

Rejuvenation of soil environments

Restoration of vegetation and soil environments on
volcanic ash deposits
Volcanic ash is a suitable medium for plant growth

114

S. SHOJI and T. TAKAHASHI

providing physical support, essential plant nutrientsand plant-available water. Therefore, rapid restoration of vegetation and soil environment commonly
takes place on volcanic ash deposits as observed in theareas of Mt. Usu, Hokkaido, Japan, Mt. Pinatubo,
Central Luzon, the Philippines, and Mt. St. Helens,
Washington, USA (see page 71).
The 1977 – 78 Mt. Usu eruptions blew out a large
amount of volcanic ash and deforested the summit
with a 1 – 3 m thick ash deposit. The ash is characterized by dacitic rock type, predominance of volcanic
glass with high vesicularity and a very coarse texture(Shoji, 1993). Though phosphorus is usually a limiting nutrient for most agricultural plants grown on
volcanic ash soils, the Mt. Usu ash contains a substantial amount of plant available phosphorus (Shoji etal., 1993b). This fact strongly suggests that nitrogenis the most important nutrient limiting revegetation of
Mt. Usu summit.
The revegetation on Mt. Usu showed two patterns
until 1990: seedling revegetation on the thick ash
deposit and vegetative revegetation on the thin ash
deposit (< 1 m) (Haruki and Tsuyuzaki, 2001;
Tsuyuzaki, 2001; Tsuyuzaki and Haruki, 1996). The
former was established by trees producing
wind-dispersed seeds such as Populus maximowiczii,
Betula platyphylla var. japonica, Salix sachalinsis, etc.
The latter efficiently proceeded from resprouting ofburied branches of Polygnum sachalinse andPetasetus japonica var. giganteus.
Mt. Usu volcanic ash soils show regosolic properties after 25 years of weathering (Shoji, 1993).
They have thin organic (Oi and Oe: 2 – 5 cm) and AC
horizons (2 – 5 cm) under various forests. The soil
samples contain oxalate-extractable aluminum plus a
half iron percentage totaling 0.42%, and their phosphate retention is 15.2% (mean of 20 soil samples
from 5 pedons). It was noted that the content ofplant-available phosphorus in the soils is almost comparable with that of the fresh ash (Truog soluble P2O5:
0.1 – 0.40 g per kg).
The violent eruptions of Mt. Pinatubo from June 9
to 16, 1991, were among the largest in the 20th century,and ejected a tremendous amount of volcanic ash on
and around the volcano. Thus, lahar or volcanic ash
moving down to the lowlands repeatedly occurred
every rainy season, so wide agricultural areas inCentral Luzon were covered with thick lahar deposits(PHIVOLCS, 1992). Mt. Pinatubo ash showed similar properties to those of Mt. Usu: dacitic rock type,abundance of volcanic glass with high vesicularity anda very coarse texture. It contains 1.7 g P2O5 kg–1
mostly occurring as apatite which enhances theplant-available phosphorus level of the ash deposits(Nakamaru et al., 2000).
Two types of intense revegetation on the lahar
deposits have been reported: revegetation by gramineous plant communities (Ota, 2002; Yoshida, 2002)
and by leguminous and gramineous plant communities(Saito et al., 2002). Saccharum sponteneum L. was
the most important gramineous plant as a pioneer. A
year and a few months after lahar deposition it
appeared as patches on the lahar deposits which contained fine ash and a small amount of soil material,
helping maintain suitable moisture content in the top
layer of the deposit (Table 1). Such lahar deposits
contained a trace amount of organic carbon and nitrogen (Sites N and S1). In contrast, a dense gramineous plant community was established seven years
later and the lahar deposit rapidly accumulated organic carbon (0.8%) and nitrogen (0.066%) (Ota, 2002).
As noted before, nitrogen supply to the pioneer
plants is the key to intense revegetation on volcanicash. There are several possible sources of nitrogen
supply to the vegetation as follows:
1. mineral nitrogen in rain water,
2. soil organic nitrogen mixed in the volcanic ashof lahar deposits
3. organic nitrogen of buried soil, and4. microbiologically fixed nitrogen.
The mineral nitrogen in rain water and soil organic
nitrogen mixed in the ash is small in amount, providing only a part of the mineral nitrogen needed toestablish dense Saccharum sponteneum communities.
Nitrogen supply of buried soil is strongly determinedby the thickness of volcanic ash and characteristics ofplant root systems. Saccharum sponteneum has ashallow root system (mostly < 20 cm), so it cannot
efficiently utilize mineral nitrogen from the buried soil
where the ash deposit is very thick. Thus, the major
source of nitrogen is considered to be nitrogen fixedby symbiotic microorganisms of Saccharum
sponteneum growning on ash deposits with suitablemoisture content (Ota, 2002).
Another kind of intense revegetation on the volcanic ash of lahar deposits was established by the

Table 1 Revegetation and nitrogen accumulation of the surface soils in a Mt. Pinatubo lahar area inMarch of 1998 (Ota, 2002).
Sampling site

Lahar deposition(year)

Depth of lahar
deposit (m)Growth ofvegetation*

Soil N content(mg kg-1)

N

1991 – 1996

> 1.25

Very sparse

10

S1

1991 – 1996

> 1.25Sparse – patches

11

S3

1991 – 1995

> 1.25

Patches

58

0.75

Dense

662

F3
1991
* Dominant species: Sacharum spontaneum.

Environmental and Agricultural Significance of Volcanic Ash Soils

co-existence of gramineous and leguminous plants.
This process was hypothesized as follows (Saito et al.,2002). Firstly, gramineous plants such as Saccharum
sponteneum start to grow from airborne seeds. It ishighly probable that diazotrophic endophytic bacteria
contribute to the growth of the seedlings of pioneer
plants by nitrogen fixation. Secondly, the airborne orflood-dispersed spores of arbuscular mycorrhizal
fungi colonize the gramineous plants and fungal density increases in the host plants. Thirdly, leguminous
seeds such as Calopogonium muconoides and Centrosema pubescens are also dispersed into the volcanic
ash and start to grow with the gramineous plants.
Since
leguminous
plantsarehighlymycorrhiza-dependent and require more phosphorus
uptake for their nitrogen fixation, the high population
density of arbuscular mycorryizal fungi stimulate theintense growth of the legumes.
Once a gramineous and leguminous plant community with symbiotic microorganisms is established,
the soil environment is rapidly restored as shown byvegetation and soil chemical data measured in 1999 –2000 (Table 2). The gramineous and leguminous
plant community (densely vegetated site) produced
ten times as much dry matter and also absorbed morethan 10 times as much nitrogen and phosphorus compared to the gramineous plant community (sparsely
vegetated site). Thus the soil under the gramineousand leguminous plant community accumulated morethan twice as much organic carbon and nitrogen compared to the soil under gramineous plant community.

115

Nitrogen also was the major nutrient limiting establishment of plants in the vicinity of Mt. St. Helens.
The nitrogen fixing lupin (Lupinus spp.) colonized
thick pyroclastic flow surfaces, resulting in rapid plantregeneration and dramatic short-term changes in soil
genesis (see page 73).
Soils in a volcanic zone versus soils in a nonvolcanic zone in Eastern Hokkaido
Volcanism commonly continues for a long timeand volcanic eruptions are repeated. The periodic
additions of volcanic ash generally improve the soil
physical and chemical properties and renew thelong-term soil productivity.
Thus soils in the
volcanic zone are markedly different in soil
productivity and other aspects from the soils in the
nonvolcanic zone as exemplified below.
Northeastern Hokkaido with a udic soil moistureregime and frigid soil temperature regime is tentatively divided into three zones according to the frequencies of volcanic ash deposition originated from
Mts. Kamui-nupuri, Mashu, etc. The ash deposition
was periodic and thicker in depth in Zone A (Nemuro
Subprefecture) to the east of the source volcanoes, andfewer and thinner in Zone B (southern Abashiri Subprefecture) to the northeast of the source volcanoes,
and none in Zone C (northern Abashiri Subprefecture)to the north of the source volcanoes. Therefore, eachzone shows contrasting soil distributions (Tomioka,
1985). Regosolic, Ordinary and Cumulic Andosols
are widely distributed in Zone A according to distance

Table 2 Vegetation and soil chemical properties of the gramineous plant community (sparsely vegetated site) andgramineous and leguminous plant community (densely vegetated site) in the Mt. Pinatubo lahar area
(Saito et al., 2002).
Sampling site

Gramineous plants

Gramineous and leguminous plants

Dominant plant species

Sacharum sponteneum
Rhychelytrum repens

Calopogonium muconoides
Centrosema pubescens

Rainy(Sept. ’99)

Dry
(Mar. ’00)

Rainy
(Sept. ’99)

Dry
(Mar. ’00)

DW production(g m–2)97 ± 26

76 ± 41081 ± 569

813 ± 285

Plant N uptake(g m–2)0.22 ± 0.06

0.17 ± 0.01

9.3 ± 0.49

3.90 ± 1.26

Plant P uptake(g m–2)0.11 ± 0.03

0.08 ± 0.01

1.20 ± 0.6

0.76 ± 0.38

Seasons of samplingStanding plant

Gramineous plants

Gramineous andleguminous plants

Difference between thetwo sites

Soil pH(H2O)

6.1

6.0

ns

Total soil C(mg kg–1)

1700

3900

**

Total soil N(mg kg–1)

85

249

**

Available soil P (Truog)(mg kg–1)

264

215

ns

116

S. SHOJI and T. TAKAHASHI

from the source volcanoes, while Brown Andosols aremost extensive, followed by Regosolic and Ordinary
Andosols in Zone B. The major soils on the plain
land in Zone C are Pseudogleys (Tomioka, 1985).
Volcanic ash depositions in Zone A took place
more than 10 times during the last 7,000 years (Kondo,
1985). Therefore, Regosolic Andosols most extensively occur in the area near the volcanoes, and havemulti-storied soil horizons. For example, Bekkai soil
classified as Thaptic Udivitrand (see Table 9 on page94) has five humus horizons from the surface to 1 m
depth. These horizons fail in the requirements forboth melanic and fulvic surface soils and the Bw horizons are weakly developed. The Bekkai soil showshigh organic carbon concentrations in the humus horizons and CEC values of 3 – 30 cmolc kg-1. All thehorizons except the upper two humus horizons show
virtual absence of KCl-extractable Al.
Table 3
SourceLocation
Classification
Physiography
Elevation
Water table
Permeability
Vegetation
ErosionParent material
HorizonOrdinary and Cumulic Andosols have formed fromthe same volcanic ashes of the Regosolic Andosols in
the area far from the volcanoes. They show improved physical and chemical properties and enhanced
soil productivity. Because each ash deposit is finer
and thinner, the weathering rate is greater and composite horizons are formed.
Brown Andosols in Zone B are mostly derived
from recent volcanic ash deposits and late Pleistocene
volcanic ash flow deposits. The Abashiri soil (Pedon
1 in Shoji et al., 1990) is an example of Brown
Andosols as described above (Table 3). It shows the
cumulative properties: the A1–2A horizons developedin the ash deposits of 250–550 years old, the 3A1 –3Bw2 horizons from an ash flow deposit of 12,000
years old and the C horizon from an older ash flow
deposit. The A1 horizon has a fine granular structure
and the 2AC to 3Bw1 horizons, a subangular blocky

Description of Abashiri soil.

Shoji, Hakamada and Tomioka, 1990
Kiyosato, Shari, Hokkaido
Brown Andosol (medial amorphic, frigid Typic Hapludand)
Level tableland
61 m M.S.L.
Not observed
Moderate
Broadleaved trees
None
Rhyolitic volcanic ash falls (0 – 20 cm; 250 – 550 years old)and volcanic ash flows (20 – 92 cm; 11,720 ± 220 years old)

Depth (cm)OA1

4 – 0:
0 – 14:2AC

14 – 20:

3A1

20 – 32:

3Bw1

32 – 58:

3Bw2

58 – 92:

4C

92 –100+:

Morphological properties
Partially decomposed organic matter.
Black (7.5 YR 2/1) moist; moderate fine granular structure;very friable and slightly sticky; abrupt boundary.
Brown (7.5 YR 4/4) moist; weak medium subangular blocky
structure; very friable and slightly sticky; abrupt boundary.
Dark brown (7.5 YR 3/3) moist; weak medium subangular blocky
structure; very friable and slightly sticky; abrupt boundary.
Brown (7.5 YR 6/6) moist; weak medium subangular blocky
structure; very friable and slightly sticky; abrupt boundary.
Brown (7.5 YR 5/5) moist; weak prismatic structure; friable andslightly sticky; clear boundary.
Brown (7.5 YR 4/6) moist; weak prismatic structure;firm and sticky; abrupt boundary.

Table 4 Selected physical and chemical properties of Abashiri soil (Shoji et al., 1990).
Depth
(cm)

HorizonClay
Bulk
content density(%)(g cm–3)

Organic
C
(%)

pH
(H2O)

CEC
KCl-extr.
Base sat.
(cmolc kg–1)
Al(%)(cmolc kg–1)

P ret.
(%)

Alo+1/2Feo#(%)

Allophane§(%)

0 – 14

A1

5

0.64

4.2

6.0

0.1

17.8

59

53

0.88

1.6

14 – 20

2AC

6

0.48

1.6

6.5

tr

10.6

49

59

1.14

2.8

20 – 32

3A1

21

0.62

2.4

6.6

tr

16.7

51

92

3.93

12.6

32 – 58

3Bw1

21

0.55

1.7

6.7

tr

14.6

48

93

4.63

17.1

58 – 92

3Bw2

27

0.75

0.7

6.5

0.1

16.9

35

94

5.37

21.5

24.4

64

72

1.94

4.4

92 – 100+
4C
29
0.88
0.3
6.5
0.1
#
Aluminum plus 1/2 iron percentages by ammonium oxalate.
§
Allophane percentages determined by ammonium oxalate extractable Si×7.1.

Environmental and Agricultural Significance of Volcanic Ash Soils

structure, and the 3Bw2 to 4C horizons, a prismatic
structure. However, all the horizons except the 4C
horizon show a friable and slightly sticky consistency.
The Abashiri soil shows bulk densities of less than
0.9 g mL–1 in all the horizons (Table 4). The clay
content is very low (5 – 6%) in the surface horizonsfrom young ash while it is considerably higher in theother horizons from the old ash flow deposits (20 –29%). Major components of clay fractions are 2:1
layer silicates, Al-humus and volcanic glass in the A1
horizon, 2:1 layer silicates and allophane-imogolite in
the 2AC horizon, allophane-imogolite in the 3A1 to
3Bw2
horizons,
andhalloysite
andallophane-imogolite in the 4C horizon. The Abashiri
soil has a large volume of total porosity andplant-available water (Shoji et al., 1990).
Accumulation of organic carbon or humus ismoderate in the surface horizons because these young
horizons are less weathered, as shown by low valuesof acid oxalate extractable Al and Fe and P retention.
In contrast the old horizons demonstrate high valuesof these analyses. The values of CEC and base saturation are 10.6 – 24.4 cmolc kg–1 and 35 – 40%, respectively. Therefore, soil acidity is mostly slightly acidto neutral and KCl extractable Al which may be toxic
to plant roots is virtually absent. As described above,
the Abashiri volcanic ash soils are high in soil productivity so that they are suitable for producing highquality crops.
The Pseudogleys in Zone C in non-volcanic zones
are formed from a fine Pleistocene terrace deposit andTable 5
SourceLocation
Classification
Physiography
Elevation
Water table
Permeability
Vegetation
ErosionParent material
HorizonDepth (cm)OA1

3 – 0:
0 – 13:

A2

13 – 20:Bg

20 – 37:BCg

37 – 67:C1g

67 – 138:C2g

138 – 160+:

117

are locally called “heavy clay soils”. This naming
suggests that they have serious physical and engineering constraints.
The Monbetsu soil was selected to show the characteristics of Pseudogleys as described above (Tables
5, 6). The surface horizons (A1 and A2) show black
to brown colors but the Bg and BCg horizons, a lightgray color, indicating a characteristic of gleying due towater stagnant and anaerobic conditions. The A2 to
BCg horizons have moderate prismatic structures withclay and organic films. The Bg to C2g horizons arealso characterized by very sticky and very plastic
consistency.
The physical properties of the Pseudogleys arestrongly determined by fine texture and abundance oflayer silicates. The Monbetsu soil shows clay contentsof 44 – 55% in the A1 to BCg horizons, bulk densities
greater than 1.1 gm L–1 and air phase ratios less than
10% in all the horizons except the A1 horizon.
These physical properties greatly reduce drainage,
plant root elongation and tractability of agricultural
machines.
The Monbetsu soil shows a very high organic carbon concentration only in the A1 horizon. The CEC
and base saturation values range from 20.5 to48.2 cmolc kg-1 and from 26 to 55%, respectively. The
soil acidity is strongly acid to moderately acid and the∆pH values are high in most horizons, suggesting anabundance of KCl-extractable Al. In fact, all thehorizons except the A1 horizon contain
KCl-extractable Al of 5 – 11 cmolc kg-1 that can cause

Description of Monbetsu soil.

Hokkaido Development Bureau, 1972
Numanoue, Monbetsu city, Hokkaido
Pseudogley (Typic Haplaquept)
Plain land on the middle terrace
Not described
Not described
Very poor
Alder, white birch, bamboo grass, bracken, etc.
None
Clayey terrace deposit
Morphological properties
Black (10 YR 1/1) moist; moderate fine granular structure: firm;
clear boundary.
Grayish yellow brown (10 YR 6/2) moist; few mottlings;
moderate coarse prismatic structure with clay and organic films; firm;
clear boundary.
Light gray (10 YR 8/1) moist; moderate medium prismatic structurewith organic films; firm, very sticky and very plastic; gradual boundary.
Light gray (10 YR 7/1) moist; moderate coarse prismatic structure withclay and organic films; firm, very sticky and very plastic;
gradual boundary.
Bright yellowish brown (10 YR 6/8) moist; weak coarse prismatic
structure; very firm; gradual boundary.
Grayish yellow brown (10 YR 6/2) moist; weak coarse prismatic
structure; firm, very sticky and very plastic.

118

S. SHOJI and T. TAKAHASHI
Table 6 Selected physical and chemical properties of Monbetsu soil (Hokkaido Development Bureau, 1972).
Depth
(cm)

Horizon0 – 13A1

44

13 – 20A2

20 – 37Bg

37 – 67
67 – 138
138 – 160+
#

Clay
Bulk
content density(%) (g cm–3)

Three phase ratio (%)

Organic
pH
C
(H2O)
(%)

pH
(KCl)

Solid

Water#

Air

0.41

20

50

30

10.5

5.2

4.1

48

1.19

45

47

9

3.0

5.6

55

-

-

-

-

0.9

5.4

BCg

50

1.18

43

54

3

0.4

C1g

35

1.22

45

51

4

0.2

C2g

33

1.31

48

49

2

0.3

KCl-extr.
Base
CEC
Al
(cmolc kg–1) sat.
(cmolc kg–1)
(%)
2.9

48.2

30

4.1

5.4

28.6

26

3.9

11.1

27.6

30

5.8

3.8

8.8

22.9

47

5.9

3.8

6.1

20.5

55

5.9

3.8

9.4

35.6

36

Field moist.

serious Al toxicity to plants roots.
It is obvious from the foregoing that there areremarkable differences in morphological, mineralogical, physical and chemical properties between the
Brown Andosols in Zone B and the Pseudogleys in
Zone C. From an agronomic point of view, theBrown Andosols have excellent physical properties
for plant growth and management, such as large
water-holding capacity available to plants, favorable
conditions for root elongation, high tractability, etc.
They also have suitable chemical properties such asslightly acid to neutral reaction, virtual absence of
toxic Al, moderate CEC values and soil organic matter
concentrations, etc. On the other hand, the Pseudogleys have poor soil tilth, difficult root penetration,and low tractability because of their fine texture, poor
drainage and abundance of layer silicates. They also
have a large amount of toxic Al in both the surface
and subsurface horizons, strongly limiting plant
growth. Thus, various improvement practices suchas mole and tile drainage, liming, deep cultivation,
subsoil breaking, and sand addition to the Ap horizon
have been traditionally recommended.
Amenity
Volcanic ash soils widely occurring in Japan also
provide a comfortable living environment or amenity
and create a favorable landscape for recreation andhuman health. Construction applications for both individual living sites and communities are favored byexcellent soil physical properties such as medium texture, low bulk density, and friable consistency of thesoils. In addition to these physical properties, thelarge water-holding capacity is highly helpful for
gardening on volcanic ash soils. Many Japanesepeople consider that vigorous plant growth andhealthy soil properties (Doran et al., 1996) create acomfortable environment.
There are a great number of scenic spots in Japanand many of them are volcanic landscapes. The
unique morphology of volcanic mountains andchanges in vegetation according to elevation create
very attractive landscapes. Volcanic ash soils on thelandscape are an excellent medium for vigorous
growth of vegetation. The landscape seasonallychanges and shows different picturesque sceneries
throughout the year. Thus, numerous people enjoysightseeing and outdoor sports in volcanic landscapes.
Amenity conservation is one of the environmental
conservation functions of agricultural land or soil. It
includes landscape conservation, microclimate modification, recreation and human health, and residential
area conservation (Yokohari et al., 2000). Volcanic
ash soils can substantially contribute to amenity conservation.
1.2 Carbon and nitrogen stocks in volcanic ash
soils
The soil can accumulate large amounts of carbon
and nitrogen as important components of soil organic
matter (SOM). SOM is the main source of nitrogen(N) for plants. For example, approximately two
thirds of N in wetland rice and a half of N in mostupland crops are microbiologically mineralized from
SOM (Shoji and Mae, 1984). SOM is also the main
source of nutrients and energy for soil organisms, so
their population and diversity decline with a decrease
in SOM. It increases cation exchange capacity andacts as a pH buffer. It also contributes to developing
stable soil structures, enhances water-holding capacity
and improves soil tilth.
There is an increasing concern about SOM in relation to mitigation of climate change by soil carbon
sequestration. It is estimated that carbon held in
SOM is approximately twice that occurring in theatmosphere as CO2 and is three times more than thatin all the vegetation as organic compounds (IPCC,
2001). However, SOM has been seriously decreased
by intense cultivation and soil erosion.
Volcanic ash soils are a major soil in Japan. They
store a great quantity of SOM which consists mainlyof stable humic acids. For example, 40% of agricultural land in Hokkaido is occupied by volcanic ash
soils (Table 7). Of the volcanic soil groups, cumulic
and gley cumulic volcanic ash soils account for 24%of the total acreage of volcanic ash soils. Since theirhumus horizons have a depth of at least 30 cm andorganic C of more than 7%, both soils contain morethan 100 Mg organic C ha–1.

Environmental and Agricultural Significance of Volcanic Ash Soils

119

day–1 (mean of 10 soils) while that of nonvolcanic ash
soils, 7.74 × 10–3 day–1 (mean of 8 soils) (Takenaka
and Hayano, 1999). Gramineous vegetation also
contributes to increasing SOM by plentiful supply ofcellulose and lignin-rich plant materials to the soil as
discussed later. Burial of volcanic ash soils by re-

There are many volcanic ash soils which have extremely thick humus horizons with a very dark color.
They were formed by repeated ash depositions andpedogenesis since the late Pleistocene as exemplified
by the Imaichi in Kanto and Takaono in Kyushu(Table 8). The Imaichi soil shows composite humus
horizons of 86 cm and contains 48.2 kg organic C m–2(482 Mg organic C ha–1) and 2.17 kg organic N m–2(21.7 Mg organic N ha–1). The Takaono soil also hascomposite humus horizons of 410 cm and has 112.4 kgorganic C m–2 (1,124 Mg organic C ha–1) and 6.58 kg
organic N m–2 (65.8 Mg organic N ha–1). Since mostfield crops uptake 100 to 300 kg N ha–1, the storedorganic N in both soils is estimated to be several
hundred fold the plant uptake of N.
There are several factors contributing to remarkable accumulation of SOM in volcanic ash soils.
SOM of volcanic ash soils is commonly predominatedby humic acid with the highest degree of humification(type A humic acid) and is complexed with active Al
and Fe in the soils. Thus, the mean mineralization
rate of organic C of volcanic ash soils is 3.02 × 10−3

Table 7 Distribution of volcanic ash soils in Hokkaido(Tomioka, 1985).

#

Soil group

Distribution (%)#

Volcanogeneous Regosols
Gleyic Volcanogeneous Regosols
Regosolic Andosols
Gleyic Regosolic Andosols
Brown Andosols
Ordinary Andosols
Gleyic Ordinary Andosols
Cumulic Andosols
Gleyic Cumulic Andosols
Total

6.5
1.6
3.5
0.3
6.3
11.5
0.7
6.8
2.9
40.1

Percentage of the total area of agricultural lands.

Table 8 Organic carbon and nitrogen stocks in Imaichi and Takaono soils with thick high-humic horizons.
Depth
(cm)

Horizon

OC
(%)

ON
(%)

Storage (kg m–2)
OC

ON

Age (YBP)

Imaichi soil# (Imaichi City, Tochigi Prefecture)0 – 13

A1

19.8

1.02

9.0

0.46

13 – 23

A2

17.8

0.85

7.5

0.36

23 – 32

2A3

16.8

0.74

6.7

0.29

32 – 46

2A4

16.0

0.66

8.7

0.36

46 – 58

3A5

12.1

0.49

5.5

0.22

58 – 74

3A6

10.5

0.45

7.0

0.30

74 – 86

4A7

1.9

0.09

1.2

0.05

86 – 121

4C

1.0

0.05

2.6

0.13

48.2

2.17

Total
§

Takaono soil (Ootsu Town, Kumamoto Prefecture)0 – 24

12.7

1.03

14.3

1.16

24 – 60

7.1

0.54

12.3

0.93

60 – 80

8.0

0.54

6.6

0.44

80 – 108

11.7

0.61

14.7

0.77

9,950

108 – 130

6.6

0.30

7.1

0.32

13,400130 – 182

5.8

0.33

13.9

0.77

15,100182 – 220

3.0

0.19

4.8

0.30

220 – 238

4.2

0.17

3.6

0.14

238 – 270

5.4

0.33

8.8

0.54

21,500270 – 285

4.5

0.20

3.5

0.16

23,500285 – 303

4.9

0.25

3.9

0.20

25,100303 – 327

3.5

0.16

3.9

0.18

327 – 350

3.1

0.13

3.2

0.13

350 – 410

4.8

0.22

11.8

0.54

Total
112.4
#
Kurobokudo Co-operative Research Group (1986)§
Kubotera, H. and I. Yamada (1995)

6.58

120

S. SHOJI and T. TAKAHASHI

peated ash depositions protects against surface horizon loss by soil erosion and human activity and retards the mineralization of SOM.
1.3 Water storage and water quality improvement
Volcanic ash soils have well developed soil structures with various pore diameters so that they can holda large amount of plant-available water as alreadydescribed by M. Nanzyo. They can supply almost
enough water to grow most agricultural plants inJapan though the plants have very high water requirement (amount of water in gram needed for
producing dry plant matter of 1 g) ranging mostly
from 100 to 600 (Shoji and Mae, 1984).
Volcanic ash soils under forests can decrease
flooding during the rainy season and can relieve water
shortages during the dry season. An analysis of thefactors contributing to water storage of forest soils(Water Utilization Res. Inst., 1983) showed that thefirst factor is the kind of soil; the second, depositionalmode of the soil material; and the third, the kind of
substrata, and that volcanic ash soils have the highest
scores in each factor (Fig. 1). When both volcanic
ash soil and its substratum are very thick, water storage is remarkably enhanced. They can also substantially decrease the amount of flooding because
gravitational water supplied by rainfall needs moretime to move down through the thick soil and substratum.
Volcanic ash soils commonly contain a large

amount of noncrystalline materials which have a large
anion exchange capacity and plenty of active Al andFe as described before. Therefore, they can help
maintain and improve the quality of ground water,river water and other water bodies by removing andretaining nitrate and phosphate originating mainly
from applied fertilizers. For example, fertilizer phosphorus remaining after crop harvest occurs mostly as
sparingly soluble forms in the plowed layer so a large
amount of the residual phosphorus is observed in thesurface horizon of volcanic ash soils under intensive
agriculture. A leaching experiment using soil columns also indicated that an allophanic volcanic ash
soil can effectively retain phosphorus in polluted
water (concentration: 100 ppm P) until the total
amount of retained phosphorus reaches approximately
50% of the phosphorus sorption quotient of the soil
(Akiyama et al., 1991).
Volcanic ash soils can retain nitrate by anion exchange reactions. This nitrate is utilized by agricultural plants as exemplified below (Kitamura et al.,1986). As presented in Table 9, a considerable
amount of nitrate (70 kg N ha–1) occurred in the subsurface horizons of an allophanic soil before transplant of tobacco plants. The plant absorbed mainly
basal fertilizer N in the early growth stage and soil
nitrate N in the late growth stage. Though plant recovery of fertilizer N reached greater than 60% at
harvest, plant uptake of soil N was more than that of
fertilizer N. Soils without positive charges repel
anions such as nitrate and chloride. This pheno-

Kinds of soils
Depositional mode
Kinds of substrata
Altitude
Topography
Kind of forest
Height of trees
0

10

20

30

40

50

60

70

80

Range of scores (L m-3)

Fig 1 Analysis of factors contributing to water storage of forest soils (Water Utilization Res. Inst., 1983).
Table 9 Mineral N in an allophanic volcanic ash soil and uptake of fertilizer and soil N by tobacco plant (Kitamura et al., 1986).
Mineral N in soil (kg ha–1)
Soil N
Fert. N0 – 20 cm 20 – 100 cm
95
22
70

Plant N (kg ha−1)

8.3

2.4

10.7

Plant recoveryof fert. N(%)
6.9

July 4

17

16

67

54.5

14.4

68.9

45.4

July 23

1

6

46

79.6

33.0

112.6

66.3

Aug 31(harvest)

0.2

1.0

24

74.5

86.8

161.3

62.1

Date
June 11

Fert. N

Soil N

Total

N.B.: Fertilizer application using conventional fertilizers: N; 120, P2O5; 240, K2O; 300 kg ha–1.
Plant recovery of fertilizer N: determined by the tracer method using 15N labeled fertilizer.

Environmental and Agricultural Significance of Volcanic Ash Soils

menon accelerates the loss of nitrate from the soil
system, finally contributing to lowering water quality
in the environment.
1.4 Preservation of paleoenvironments andarchaeological artifacts
Intermittent volcanic ash deposition and repeatedpedogenesis commonly create sedentary multi-storied
soils in Japan. For example, the Takko soil in southeastern Aomori Prefecture, Tohoku has a five-storiedsoil profile formed from Towada Holocene ashes(Saigusa et al., 1978) and the Miyakonojo soil in
Miyazaki Prefecture, Kyushu, an eight-storied soil
profile from Holocene ashes of several volcanoes(Inoue, 2001). Such sedentary multi-storied volcanic
ash soils notably resist soil disturbance, truncation,and displacement due to natural and human activities.
Thus they serve as a heritage to preserve in their materials and profiles highly useful information which is
integrated over the period of pedogenesis.

Fig. 2

121

Preservation of the soil environment
Soil burial by intermittent ash depositions strikingly reduces the effects of climate and organisms on theburied soils. For example, there occurs notable reduction of diurnal changes in soil temperature andmoisture, organic matter supply from the vegetationand microbial activity. Therefore, their weathering
rate is significantly lowered, so the soil properties aresubstantially preserved for several thousands of years
after burial as Inoue (2001) has shown by comprehensive studies on the Miyakonojo soil.
The Miyakonojo soil shows a very deep,
multi-storied profile formed from repeated volcanic
ash depositions ranging from 23,000 to 88 YBP(Fig. 2). It had two intense humus accumulation
periods: 6,500 to 4,200 YBP and 4,200 to 500 YBP.
The 4A and 2A horizons contain organic carbon
concentrations greater than 10%.
All the soil horizons have bulk density values
smaller than 0.85 g mL-1 and most of them (except the
young soil horizons (1,500 YBP) and the lowermost
horizon) show phosphate sorption quotients greater

Selected properties of Miyakonojo volcanic ash soil (Inoue, 2001).
BD; bulk density (Mg m–3), PSQ; phosphate sorption quotient (g P2O5 kg–1), OC; organic carbon (g kg–1),
HA type; humic acid type.

122

S. SHOJI and T. TAKAHASHI

than 1500 mg P2O5 per 100 g soil (equivalent to phosphate retention of 85%). This fact demonstrates thatthe buried soil horizons still maintain andic soil properties even after 23,000 years.
Noncrystalline aluminosilicates such as allophane
and imogolite, and halloysite are characteristic of clay
weathering in volcanic ash soils. The abundance ofallophane and imogolite commonly increases with anincrease in silica leaching while the abundance of
halloysite increases with a decrease in silica leachingor silica enrichment in the soil profile (Saigusa et al.,
1978; Parfitt et al., 1984). This is also the case for
the Miyakonojo soil which shows a predominance ofallophane and imogolite in the surface to the 7A/C2
horizon (7500 YBP) and then increases in halloysite
content in the deeper horizons which are subject tosilica enrichment.
As the Japanese word “Kurobokudo” (meaning“black-flully soil) suggests, volcanic ash soils in Japangenerally contain large amounts of very dark organic
matter which is dominated by type A humic acid withthe highest degree of humification. As presented inFig. 2, the Miyakonojo soil also shows the existenceof type A humic acid in all the humus horizons except
the Ap horizon. SOM content of eight humus
horizons ranges from 21.2% (OC: 12.3%) to 5.47 %(OC: 3.17%) with a mean value of 11.3% (OC:
6.54%). Most of these horizons meet the melaniccolor requirement (a color value, moist, and chroma of
2 or less).
Plant opal studies on volcanic ash soils haveshown that development of the very dark humus horizons in “Kurobokudo” is attributable to grass vegetation induced by human activity since the late Pleistocene (Sase and Hosono, 1996; Sase and Kato, 1976;
Sase and Kondo, 1974). Employing plant opal
analysis, Inoue (2001) also confirmed the important
contribution of gramineous plants to the accumulationof SOM in the Miyakonojo soil. Furthermore, he has
indicated that the buried soil horizons still virtually
maintain their original organic carbon concentrations.
The factors in the high stability of soil organic matter
under buried conditions are considered as follows: 1)
predominance of type A humic acid, 2) formation of
stable Al/Fe-humus complexes, and 3) low soil
microbial activity.
Preservation of paleovegetation
As described before, volcanic ash soils in Japan
have a very dark humus horizon from which the term
“Kurobokudo” or “Ando” originated and grass vegetation is closely associated with the formation of thedark humus horizons. Since forest vegetation isnatural and very common in Japan where ahumid-temperate climate prevails, grass vegetation is
induced by strong human activity such as fires,
grazing, cutting, etc.
Grass vegetation types differ with differences inclimatic conditions: Miscanthus type in the

cool-temperate zone and Miscanthus type andPleioblastus type in the warm-temperate zone
(Numata, 1974). Therefore, the kind of gramineous
plants contributing to the formation of dark humus
horizons varies widely with differences in climaticconditions.
Plant opals are highly resistant to chemical weathering under acid soil conditions, so microscopic
observation of soil materials is very useful for finding
paleovegetation. In addition, the stable carbon isotope ratios of soil organic matter can be employed asindicators of vegetation and climate changes (Bouton,
1996; Yoneyama and Yoshida, 2000).
Figure 3 shows the vertical distribution of dry
matter production of gramineae in the Holocene
Miyakonojo soil horizons. Miscanthus (C4 plants) isdominant in the 7A/C2 to 8A1 horizons. Then
Pleioblastus sect. Medake and Pleioblastus Nezasa
are remarkably increased, especially in the 4A to 5A
horizons and 2A to 3A horizons. A tremendous
number of plant opals were observed for these humus
horizons. For example, 69,000 particles g–1 soil of
Nezasa and 37,000 particles g–1 soil of Medake werecounted in the lower part of 4A horizon. The highest
dry matter production of each plant is estimated to be
more than 300 g kg–1 soil. Thus plant opal analysis
provides useful information integrated over the periodof pedogenesis.
Preservation of archaeological artifacts
Numerous archaeological remains and artifacts
have been extensively found in Holocene volcanic ash
soils in Japan (for example, Kuwahata and Higashi,
1997; Takahashi et al., 1983). This fact indicatesthat human activity was remarkably enhanced after thelate Pleistocene.
Sedentary multi-storied volcanic ash soils are an
excellent artifact preserver and a chronologic indicatorwith evidences of environmental conditions andhuman activity. They are clearly different in morphological, physical and chemical properties fromarchaeological artifacts and human-modified soils.
In addition, low bulk density, and friable and nonsticky consistency of the soils are highly helpful incarrying out precisely and efficiently the excavation
work.
Multi-storied volcanic ash soils provide a series oftermination points for soil development so thatarchaeological artifacts chronologically occur in thesoil profiles as exemplified in the Miyakonojo soil
(Kuwahata and Higashi, 1997). In this profile
numerous artifacts produced in the late Paleolithic,
Jomon, Yayoi and Kofun periods are chronologicallyobserved. The main tools contained in the soil horizons of the Paleolithic period (below approximately
3 m depth) are lithic artifacts. A variety of pottery
types are present in the soil horizons of the Jomon to
Kofun periods (above 3 m depth).

Environmental and Agricultural Significance of Volcanic Ash Soils

123

Fig. 3 Plant opal analysis of Miyakonojo volcanic ash soil (Inoue,2001).

2. Utilization of Volcanic Ash Soils andTheir Properties Relating to Soil Productivity
2.1 Soil productivity
As reviewed by Shoji et al. (1993b), volcanic ash

soils are among the most productive soils in the world
and that explains why these soils have a high humancarrying capacity. In contrast, volcanic ash soils inJapan formed under a humid-temperate climate wereoriginally regarded as poorly productive soils becauseof very low content of plant-available phosphorus,
low concentrations of exchangeable bases and strong

124

S. SHOJI and T. TAKAHASHI

acidity (Nomoto, 1958). However, these chemical
constraints are easily improved by phosphorus fertilizer application and liming.
Some volcanic ash soils in Japan are especially
productive for growing upland crops and their notableproperties are summarized by Shoji (1979) as follows:(1) Parent material: basaltic ash,(2) Morphology: pachic (thick humus-rich horizon) indicating intermittent ash depositions and repeated pedogenesis,

yams, which were extensively introduced into thisarea in the 1970s as shown in Fig. 4. The acreage ofChinese yams reached a high value in the late 1970s
and has since remained steady without significant
change. The climate is characterized by cool summers for which root crops are well adapted. The
major soils of the area are allophanic Melanudands
and Hapludands formed from intermittent volcanic
ash depositions (Shoji et al., 1993a). The surface tothe deep horizons of these soils have uniform physical

Table 10 Vegetables suitable for growth in volcanic ash soils and important soil properties contributing to high quality
production at special production localities.
PlantsSpecial production locality

Important soil properties

Chinese yam

Towada, Aomori Pref.

1. Low bulk density and friable consistency
2. Uniform physical and chemical soil properties

Edible burdock

Mito, Ibaraki Pref.

1. Good drainage
2. Uniform physical and chemical soil properties
3. Absence of toxic Al

Japanese radish, cabbage, andwater melon

Miura, Kanagawa Pref.

1. Stable soil structure
2. Friable consistency
3. Fertile soils derived from basaltic tephras

Japanese radish, edible burdock,taro, sweet potato and ginger

Miyazaki Pref.

1. Friable consistency
2. Stable soil structure
3. Abundance of plant-available water
4. Absence of toxic Al(3) Physical properties: medium-texture and absence of sharply contrasting textural discontinuities,
friable consistency, free drainage, and highplant-available water content, and(4) Chemical properties: high base saturation,
pH (H2O) > 6.0, absence of toxic Al, accumulation ofgreat amounts of organic matter, and good natural
supply of plant nutrients.
2.2 Utilization of volcanic ash soils
A variety of agricultural crops have been grown on
volcanic ash soils : wheat, barley, rice, sweet potatoes,
peanuts, vegetables, etc., in the warmer regions, andpotatoes, wheat, sugar-beets, various beans, etc., in thecooler regions. However, utilization of volcanic ash
soils in Japan has been largely changed with remarkably increased importation of grain crops since the1970s. Nowadays volcanic ash soils are most extensively used for growing high value horticultural crops
and their properties are conducive to development of
production localities as exemplified in Table 10.
For example, Chinese yams (Discoria batatas) area glutinous vegetable and Japanese people are very
fond of their mashed raw material. High quality
Chinese yams show a baseball bat shape that is easily
broken. Therefore, excellent soil tilth is essential not
only for smooth elongation of the roots but also foreasy harvesting. The Towada area in Aomori Prefecture is the largest production center for Chineseand chemical properties due to cultivation that aresuitable for growing high quality Chinese yam.
2.3 Properties relating to soil productivity
Chemical properties
Nitrogen: Although the percentage of readily mineralizable organic N in the pool of organic N is rather
small in volcanic ash soils, these soils often accumulate high concentrations of organic matter that contains appreciable quantities of organic nitrogen.
Therefore, volcanic ash soils commonly supply large
amounts of mineral nitrogen to crops.
Saito (1990) compared the N mineralization potential (No) to the pool of total organic N (Nt) between
volcanic ash soils and non-volcanic soils from northeastern Japan and showed that the percentage of mineralizable N (No / Nt values) of volcanic ash soils(mean: 3.5%) is less than half that of non-volcanic
soils (mean: 8.2%). This suggests that organic N in
volcanic ash soils is highly resistant to microbial
decomposition.
However, a comparison ofsoil-derived N with the amount of fertilizer N in theplants indicates that the supply of soil-derived N or
natural supply of N is very important even for plants
grown under heavy N fertilization: the soil-derived N
absorbed by several agricultural crops (corn, sorghum,
winter wheat, sugar beets and tobacco) grown on volcanic ash soils amounted to 62 – 101 kg N ha–1 (Shojiet al., 1993b).

Environmental and Agricultural Significance of Volcanic Ash Soils

125

1200
Wheat and its group(1240 ha)Index (1972=100)

1000
800
600

Chinese yam(2730 ha)

400
200
0
1998

1996

1994

1992

1990

1988

1986

1984

1982

1980

1978

1976

1974

1972

Pulses(soybean etc.)(4320 ha)Fig. 4 Changes in acreage of upland crops in Aomori Prefecture(from the statistical data of the Ministry of Agriculture, Forestry and Fisheries, Japan).

Nitrogen is required in large quantities by mostagricultural plants throughout their growth period.
The use of N fertilizer has dramatically increased
yields of agricultural plants, but recovery of N fromordinary fertilizer sources such as urea and ammonium sulfate by plants is generally not high. Inorganic forms of N, mainly nitrate-N, occur in thesubsurface horizons of volcanic ash soils used for
upland crops. The inorganic pool of N can significantly contribute not only to the yield of upland crops,
but also to pollution of surface and ground water byleaching. Excess uptake of N especially in the later
growth stages causes deterioration in the quality of theharvest. To resolve these problems, nowadays we
can select the precision agricultural methods using
controlled release fertilizers as discussed later.
Phosphorus:
Phosphorus
is
often
the
growth-determining nutrient element for agricultural
crops on recently reclaimed volcanic ash soils because
its supply is often very low. The element is strongly
sorbed by noncrystalline aluminum and iron materials,
making it sparingly available for plant uptake.
Fresh volcanic ash contains a certain amount ofphosphorus that is readily soluble in acid solutions.
For example, fresh volcanic ash samples from Tohoku
and Hokkaido contain total phosphorus ranging from0.07 to 0.28% as P2O5 (average: 0.15%) (Nanzyo etal., 1997). Apatite appears to be the primary
phosphorus-bearing mineral and is fairly soluble inacid solutions contributing to rapid revegetation on
volcanic ash deposits (Nakamaru et al., 2000). Thus,
phosphorus is not always a limiting nutrient element
in revegetation of ash-covered lands, as mentioned
earlier, contrasting with the fact that many crops sufferfrom severe phosphorus deficiency when they aregrown on newly reclaimed volcanic ash soils.
Plants can absorb soluble phosphorus and weakly
bound forms of phosphorus. Applied phosphorus
readily reacts with weathering products of volcanic
ashes such as noncrystalline aluminum and iron mate-rials, resulting in the formation of insoluble
metal-phosphorus compounds. According to a kinetic study of chemical weathering in young volcanic
ash soils with udic soil moisture regimes from northeastern Japan (Shoji et al., 1993c), it was predictedthat only a few hundred years is required to form soils
with acid oxalate extractable Al + Fe/2 ≥ of 0.4% andP retention > 25%. Thus, most agricultural plants
grown even on young volcanic ash soils show phosphorus deficiencies. Farming of these volcanic ash
soils requires heavy application of phosphorus fertilizers to obtain optimum crop yields.
Not only low phosphorus supply, but also strong
aluminum toxicity and low base saturation are common limitations for crop production in nonallophanic
volcanic ash soils. Liming prior to phosphorus application is recommended for these soils. Recoveryof fertilizer phosphorus by agricultural plants in volcanic ash soils commonly is less than 20%. Band
placement of phosphorus fertilizer instead of broadcasting is commonly practiced in order to avoid therapid chemical reaction of phosphate with active Al
and Fe compounds that results in a decrease of phosphorus availability. In addition, co-situs applicationof controlled release fertilizers has been encouraged(Shoji and Gandeza, 1992).
Potassium: Potassium along with nitrogen andphosphorus is one of the major nutrient elements required in large quantities by plants. Potassium ispresent in considerable amounts in fresh volcanic
ashes; total potassium ranging from 0.5 to 4.0% as
K2O (Shoji et al., 1975). Thus, a 10 cm depth of
volcanic ash contains a large amount of potassium
ranging from 7.5 to 60 Mg per ha as K2O, assuming abulk density of 1.5 g cm–3. However, the available
forms of potassium are often insufficient for continuous cropping, especially under humid climatic conditions.
The potassium supply of volcanic ash soils isstrongly governed by the content of K in volcanic ash

126

S. SHOJI and T. TAKAHASHI

and soil clay mineralogy. It is low in the soils
formed from basaltic ash due to the low content foundin basalt. It is also strongly determined by whether
weathering reactions lead to the formation of nonallophanic or allophanic soils. Potassium is largely
retained by 2:1 layer silicates in nonallophanic soils
and tends to accumulate with advance of weathering.
In contrast allophanic clays do not show preferential
retention of K, so the amount of K tends to decrease
with the advance of weathering.
Application of potassium fertilizers influences contents of exchangeable potassium in volcanic ash soils.
Continuous heavy applications of potassium haveremarkably increased the exchangeable potassium
levels in cultivated volcanic ash soils of Japan. The
content differs widely and only a small number of
volcanic ash soils show values less than 0.3 cmolc kg–1
which is the critical level for potassium deficiency inmany agricultural plants.
Micronutrients: Several deficiencies of various
micronutrients in volcanic ash soils have beenreported. The most prevalent among them are Cu,
Zn and Co. The abundance and availability of thesemicronutrients in volcanic ash soils are dependent on
the abundance of the elements in the volcanic ash andon their release rates by chemical weathering (Shoji etal., 1993b). For estimating their plant availability,
chemical soil tests are usually used. The major categories of micronutrient extractants are dilute acids (e.g.
0.01 M HCl) and/or solutions containing chelating
agents (e.g. EDTA).
Soil acidity: It was commonly considered earlier
that there were few volcanic ash soils which had morethan traces of KCl-extractable Al and pH values lessthan 5.2, even though their base saturation was well
below 10% (Smith, 1978). This concept was completely altered by the discovery of nonallophanic volcanic ash soils in northeastern Japan that have a clay
fraction dominated by 2:1 minerals, strong to verystrong acidity, and the presence of large amounts of
KCl-extractable Al (Shoji and Ono, 1978). In contrast with allophanic soils, nonallophanic volcanic
soils cause serious acid injury or aluminum toxicity toplant roots. Even when the base saturation of allophanic volcanic ash soils is very low, they rarely have
pH values less than 5 and few of these soils experience aluminum toxicity problems. However, someplants grown on such soils show retarded growth due
to Ca deficiency.
One of the most effective ways of overcoming thefactors limiting plant growth in acidic volcanic ash
soils is lime application. This practice is rather easy
if the objective is only to improve the acidity of surface soil. However, it is very difficult to improvesubsoil acidity by liming because lime has such
limited solubility that it reacts only in the surface soils.
The subsoil substantially influences plant growth andyield because of its storage of large amounts of waterand plant nutrients, so strongly acidic subsoil poses alimitation to crop performance. To improve subsoil
acidity, surface application of gypsum or phosphogypsum is recommended because these chemicalcompounds have higher solubility compared with lime
and its Ca and sulfate can move down to the subsoil(Saigusa et al., 1994).
On the other hand, it is worth noticing that nonallophanic volcanic ash soils are regarded as a suppressive soil because the exchangeable or soluble Al
can control some soil-borne diseases of crops such ascommon bean root rot (by Fusarium solani f. sp.
phaseoli; Furuya et al., 1979) and potato common
scab (by Streptomyces scabies; Mizuno and Yoshida,1993). Thus common bean farming in the Kitami
district, Hokkaido, is adapted for that soil condition:
the plant is grown at the concentration of toxic soil Al
that is low enough so that phytotoxicity does not occur
and high enough to ensure that the disease incidence iskept within limits (Furuya et al., 1999). For potato
farming, single basal application of ammonium sulfate
to each tuber planting row is recommended. Thisapplication can efficiently lower the soil pH and increase the concentration of water soluble Al to suppress potato common scab (Mizuno et al., 2000).
Physical properties
Most volcanic ash soils have excellent physicalproperties such as high water-holding capacity, favorable tilth, and strong resistance to water erosion.
These properties contribute to enhancing the productivity of volcanic ash soils as shown in Table 10.
Development of aggregates in volcanic ash soils is
closely related to the retention of large amounts ofplant-available water. Young volcanic ash soils havea greater amount of macropores larger than 100 µm in
diameter and a lesser amount of micropores (< 0.4 µm)
and mesopores (0.4 – 6.0 µm). In contrast, moderately
weathered volcanic ash soils have a large amount of
micropores (< 0.4 µm) and mesopores (0.4 – 6.0 µm),
contributing to the large plant-available water holding
capacity (Furuhata and Hayashi, 1980). An unusually high amount of micropores in allophanic
volcanic ash soils is attributable to the intra- andinter-particle pores of allophane (Wada, 1989).
Tilth is the physical condition of a soil related to its
ease of tillage, fitness as a seed-bed, and its suitability
for seedling emergence and root elongation. Most
volcanic ash soils show excellent tilth. Cultivationof volcanic ash soils with low bulk density and friableconsistency requires less energy and can easily produce favorable seed- and root beds. Volcanic ash
soils show strong resistance to compaction even when
they are intensively used for upland farming for a longtime period. This indicates that the aggregates ofthese soils are highly stable, being cemented by noncrystalline materials and soil organic matter.
Water erosion often drastically diminishes the pro-

Environmental and Agricultural Significance of Volcanic Ash Soils

ductivity of a soil. In general, volcanic ash soils
show a strong resistance to water erosion. The
related factors include rapid infiltration that reduces
runoff and strong resistance to dispersion of soil
aggregates. The rapid infiltration rate is determinedby the content of macropores, the water permeabilityof the soil profile, and the water content of the soil.
Most volcanic ash soils have large amounts of macropores and are highly permeable. Microaggregates involcanic ash soils show strong resistance to dispersion.

3. Sustaining Volcanic Ash Soils
Volcanic ash soils in Japan are mostly utilized for
upland farming, and various farming practices are
employed to enhance agricultural production. However, unsuitable management, especially for intensive
upland farming, often results in an unbalance of plant
nutrients in the soils, decrease of soil organic matter
crucial to overall soil quality, degradation of soil
structures, and increased populations of soil borne
diseases and nematodes. In order to solve these
problems and to sustain volcanic soils, crop rotation,soil improvement, and precision agriculture with programmed fertilization using controlled fertilizers areencouraged.
Recommended rotations for crops with high economic advantages also include crops useful for controlling soil-borne diseases and nematodes, and gramineous crops to contribute to enhancing soil organic
matter and biodiversity. As plant-available soil phosphorus and efficiency of phosphorus use are generally
low in volcanic ash soils, heavy phosphorus application is commonly practiced by Japanese farmers so
residual fertilizer phosphorus is notably increased.
In order to efficiently use this phosphorus, crops thathave strong symbiotic interactions with arbuscular
mycorrizha are encouraged to be included in cropping
systems.
Volcanic ash soils commonly show multi-storied
profiles formed from different ashes. Some of them
have soil horizons strongly inhibiting plant root development. Examples include a pumice or scoria
derived soil horizon and an extremely weathered soil
horizon. Soil improvement by deep cultivation andsoil mixing, and liming and phosphorus application
are most useful for enhancing soil productivity. Volcanic ash soils also show spatial variability in various
respects, so precision agriculture is highly useful.
On the other hand, programmed fertilization using
controlled release fertilizers with high performance ismost practical, especially for intensive agriculture on
small-scale fields.
3.1 Crop rotations
It is well known that crop rotation has various
contributing factors such as increased soil nutrient

127

availability, development of favorable soil structures,
improvement of soil water availability, enhanced biodiversity, weed control, and mitigation of damage
from soil born diseases, nematodes, etc. Thus, use ofcrop rotation was repeatedly recommended to farmers.
However, traditional crop rotation in Japan has been
largely abandoned because of extensive availability ofchemical fertilizers and agrochemicals since the1960s.
Volcanic ash soils are one of two major agricultural soil groups in Japan and are mostly used for upland farming, which has notably changed with thedrastic changes in the Japanese economic structuresince the 1970s. The importation of grain crops has
remarkably increased and their acreage in Japan has
drastically decreased. It was in such an environmentthat high-value crops or horticultural crops were extensively introduced to volcanic ash soil areas.
Recently increasing impacts of intensive agriculture on the environment and safety of agricultural
products have aroused a strong interest in the evaluation and reintroduction of crop rotation among agronomists and farmers. Thus, various crop rotation
systems have been proposed and recommended indifferent areas as exemplified below. They involve a
limited number of leading crops with high economic
advantages and make full use of the excellent properties of volcanic ash soils such as friablility and nonsticky consistency, easy tillage, good aeration anddrainage, high water-holding capacity, and absence of
toxic Al. It is worth noticing that high-value root
crops are extensively selected as leading crops
because they are suitable for preservation andlong-distance transportation, and are preferentiallygrown as specialties indigenous to volcanic ash soils
in each area.
Southern Tokachi Subprefecture, Hokkaido
The volcanic ash soils in this area are mostly
Brown and Ordinary Andosols with medium soil texture (Tomioka, 1985). They have multi-storied horizons formed from several Holocene volcanic ashes
and were originally very low in plant available phosphorus. Therefore, phosphorus fertilizer has beenheavily applied.
Most farmers of this area have practiced intensive
agriculture to produce high quality potatoes and beans,and sugar beets which are protected by a government
production program. However, use of agrochemicals
to control soil-borne diseases and nematodes is mostly
limited, so the farmers are encouraged to introduce
crop rotation such as 4-year rotation of sugar beets –beans – winter wheat – potatoes (Extension Center for
Agricultural Improvement in Southern Tokachi
Subprefecture, 2001). This system can effectively
control root-knot nematodes but is poor at checking
root-rotting nematodes. Thus, including wild oats
instead of winter wheat is recommended.
Recently, root crops such as Chinese yams, edible

128

S. SHOJI and T. TAKAHASHI

burdock, radish and carrots have been recommended
to be included in the rotation systems. However,they also need cropping sequences to control nematode populations.

are multi-storied soils with thick humus horizons(Inoue, 2001) and have properties suitable for raisinghighly economical root crops such as sweet potatoes,
edible burdock and radishes. These leading crops arevery resistant to typhoons and water stress but are
badly damaged by plant parasitic nematodes. Sincemany chemical nematocides are no longer available, acropping system to effectively control nematode
populations is the key technology for maintaining the
production of high quality root crops. For this purpose, a desirable cropping sequence has been proposed as follows (Mochida, 2002): Sweet potatoes – root
crops (radishes, edible burdock, carrots, etc.) –gramineous plants for feed. The gramineous plants
also serve as cleaning and anti-nematic plants.
There are some recommended crop rotation
sequences and their evaluations in this area. Of thesesystems two systems are shown in Table 12 (Miyakojo
Council of Rational Fertilization and Prevention ofHarmful Insects and Diseases, 2001). For example,
System 1, involving sweet potatoes as the leading cropis helpful for improving soil physical and chemical
properties. However, this system is likely to bedamaged by soil-borne diseases and nematodes
because it repeats sweet potato cultivation three times
for 4 years and involves other crops sensitive tonematodes. System 6 lacks continuous monoculture
and includes anti-nematic plants such as peanuts.
Thus it can effectively control both soil-borne diseases
and nematodes. However, edible burdock, taro andWelsh onions need heavy fertilization, probably
resulting in water pollution.

Eastern area of Aomori Prefecture
Volcanic ash soils with thick dark humus horizonsin this district (Shoji et al., 1993b) are extensively
used to produce high quality Chinese yams (Department of Agriculture, Forestry and Fisheries, Aomori
Prefecture, 2002).
They are multi-storied soils
formed from five Holocene ashes from the Towada
caldera and have allophanic clay mineralogy and excellent physical properties useful for growing root
crops as already described. Uniform physical andchemical properties from the surface to the deep horizons (0 – 110 cm) attained by deep cultivation are
required for high quality Chinese yam farming.
Chinese yams are the leading crop with higheconomical advantages in this area (Fig. 4), but they
are susceptible to a root-rotting disease, seriously
reducing the yield and quality as shown in Table 11.
This disease is easily caused by continuous monoculture of the plant so crop rotation is strongly encouraged. Involvement of high value root crops such as
garlic, Welsh onion and Sudax in the rotation
sequences can completely control the root-rotting
disease. On the other hand, soil sterilization using
chloropicrin is not as effective as crop rotation incontrolling the disease.
Southern Miyazaki Prefecture
As already described, volcanic ash soils in this area
Table 11

Crop rotation of Chinese yams to control root-rotting disease(Aomori Upland and Horticultural Crops Exp. Sta., 1995).
Experiment year

Cropping system

3rd
4th
5th
6th
7th
Crop
CY
WO
S/G
G/S
CY
Rotation 1
Disease attacked (%)
21.8
0
Crop
CY
CY
S/G
G/S
CY
Rotation 5
Disease attacked (%)
0
0
0
Crop
CY
CY
CY
CY
CY*
CY*
CY
Monoculture
Disease attacked (%)
0
0
2.5
40.0
16.5
11.0
97.5
Planted crops. CY: Chinese yams, WO: Welsch onions, G: garlic, S: Sudax (plowed into the surface soil). *Soilsterilization using chloropicrin before planting.
Table 12System

1st
CY
0
S/G

Four-year crop rotation systems and their evaluations(Miyakonojo Council of Rational Fertilization and Prevention of Insects and Pests, 2001).

1st year

2nd year-----------------------------

1

2nd
CY
0
G/S

3rd year-----------------------------SP

SP------------------------------

6

SP------------------------------EB

WO------------------------------TR

RD---------------------------

WO

IR----------------------------OT---------------------------------------------------------

4th year-------------------------------------------------

PN-----------------IR

Recommended crops: SP = sweet potatoes, IR = Italian rye, WO = Welsh onions, OT = oats, RD = radishes, EB = edible
burdock, TR = taro, PN = peanuts.

Environmental and Agricultural Significance of Volcanic Ash Soils

Crop rotation efficiently utilizing soil phosphorus
Volcanic ash soils generally contain large amountsof active Al and Fe that easily react with phosphorus
to form poor soluble chemical compounds. Therefore, fertilizer efficiency of phosphorus use by plants
grown on these soils is very low, so heavy doses ofphosphorus fertilizer are commonly applied by many
farmers. Consequently, remarkable accumulation ofresidual phosphorus occurs in the surface horizon of
volcanic ash soils, so a cropping system to efficiently
utilize soil phosphorus is eagerly desired.
There are two ways of using cropping systems toefficiently enhance plant uptake of poor soluble soil
phosphorus. One is to involve plants in the systemthat can exude organic acids from their roots to dissolve soil phosphorus.
Chickpeas, buckwheat,
pigeonpeas, peanuts and rice belong to this plantgroup (Arihara, 1999). The other is to include plantsthat can have symbiotic interactions with arbuscular
mycorrhiza (AM), promoting plant uptake of the soil
phosphorus (Arihara and Karasawa, 2000; Karasawa
and Arihara, 2000). This contribution of AM has
been shown by the fact that there are close positive
linear correlations between AM colonization andphosphorus uptake of maize and between phosphorus
uptake and growth of maize raised in a volcanic ash
soil (Arihara and Karasawa, 2000; Karasawa andArihara, 2000).
As presented in Fig. 5, the grain yields of the succeeding maize are remarkably influenced by the kindsof the previous crops at both phosphorus-applied andnon-phosphorus plots. For example, the grain yields
of maize after sunflower are approximately three-foldat the phosphorus applied plot and six-fold at the
non-phosphorus plot compared with those of maize
after rape. The effect of previous crops to the growthand yield of succeeding crops is considered asfollows: the previous crops enhance AM population in
the soil helping increase AM colonization of thesucceeding crops. The increased AM colonization

0.0
Rape
Rape
Fallow
Fallow
Sugar beets
beet
Sugar
Wheat
Wheat

2.0

enables the succeeding crops to uptake more soil
phosphorus and thereby promotes their growth andyields.
3.2 Soil improvement
As described by M. Nanzyo, there are many physical, chemical and mineralogical characteristics indigenous to volcanic ash soils. Some of them contribute to important constraints on plant growth whileothers are useful for enhancing soil productivity.
Selected topics are described here (Shoji et al.,1993b).
Amelioration
The surface horizons of Japanese volcanic ash soils
formed under a humid climate are divided into allophanic and nonallophanic groups according to clay
mineralogy. The allophanic surface horizons haveallophane-imogolite and Al/Fe humus complexes as
major components of the clay fraction while thenonallophanic surface horizons have Al/Fe humus
complexes and 2:1 layer silicates. Thus both groups
contain large amounts of active Al and Fe so soil
phosphorus fertility and plant use efficiency of phosphorus fertilizer are very low. In order to improve
this problem, initial application of a large amount ofphosphorus fertilizer by broadcasting and then yearly
application of phosphorus fertilizer by banding arecommonly practiced.
Allophanic surface horizons originally contain asmall amount of exchangeable Ca ions reflecting
strong leaching so it needs liming to supply Ca ions to
the plant. On the other hand, the nonallophanic
surface horizon has a substantial amount of exchangeable Al ions or toxic Al which may damage plant roots.
Thus liming is necessary to mitigate toxic Al damage
to the plant roots.
Subsoil improvement
Mg ha-1
4.0

6.0

8.0

Phosphorus application

0 kg ha-1
87 kg ha-1

PotatoPotatoes
SoybeanSoybeans
Maize
Maize
Sunflower
Sunflowers
Fig. 5129

Effect of cultivation of crops in 1990 on grain yields of succeeding maize in 1991
(Arihara and Karasawa, 2000).

130

S. SHOJI and T. TAKAHASHI

Volcanic ash soils are generally formed from repeated volcanic ash falls. Therefore, it is not uncommon that their multi-storied horizons have notably
different properties and some subsurface horizons
show serious constraints on plant growth. Such subsurface horizon soils to the depth of approximately
1 m are improved as described below.
Soil horizon sequences to the depth of 1 m andimprovement of problem horizons are summarized asfollows (Kikuchi, 1987; Kubotera, 2001):
1. Ap horizon – very coarse textured soil – medium
textured soil with high humus content.
The second horizon is commonly formed frompumice or scoria and is less weathered. The countermeasure for this soil profile is to cultivate to thethird horizon and mix the three horizons.
2. Ap horizon – medium- or fine-textured soil with alarge amount of very active Al and Fe.
The second horizon is most weathered and is very
low in soil fertility. The countermeasure for this soil
profile is to apply amendments such as fused phosphate, superphosphate and gypsum to the upper part ofthe second horizon without mixing them with the Ap
horizon.
3. Ap horizon – indurated soil with a low degree of
weathering – medium- or fine-textured soil.
The second horizon has serious constraints such as
inhibition of plant root elongation, difficult cultivation,and poor water permeability. The countermeasure ismechanical breaking or removal of the indurated horizon.
4. Ap horizon – medium or fine textured soil withhigh soil fertility.
The second horizon includes not only volcanic ash
soil but also alluvial soil. Deep cultivation (plowing)
and mixing the Ap and second horizons can remarkably enhance soil productivity.
Conservation tillage
No-tillage has important conservation advantages
such as minimum erosion, soil moisture conservation,and minimum fuel and labor costs. It can be easily
introduced to upland farming of volcanic ash soils
because they have a friable, nonsticky consistency,
large total porosity, and strong resistance to consolidation by mechanical pressure.
In no-tillage the soil is left undisturbed and only
furrows for planting and fertilization are prepared.
When controlled release fertilizer is applied, single
basal application with co-situs placement can be employed and can increase nutrient use efficiency andyields of crops (Inoue et al., 2000).

3.3 Precision agriculture and programmed fertilization using CRFs
Spatial variability of volcanic ash soils and precision agriculture
Spatial variability of volcanic ash soils is strongly
determined by repeated depositions, dispersal patterns,
texture, and thickness of the volcanic ashes and mineralogy of the volcanic ash soils (Shoji et al., 1993a).
For example, the dispersal patterns of volcanic ash arehighly dependent upon high altitude winds (commonly westerly in the middle and high latitudes), theviolence of the volcanic eruptions, and type of volcanic ejecta. Volcanic materials blown by volcanic
explosions commonly fall predominantly east of the
volcanoes. Volcanic ash deposits show lateral andvertical variations in their texture and mineralogy.
The largest and heaviest particles tend to fall nearest
the volcanoes, while smaller and lighter particles fallat increasing distances. Such volcanic ash depositions are closely related to the spatial variability of
volcanic ash soils. For example, vitric soils nearest
to the volcano, haplic soils in intermediate areas, andmelanic soils farthest from the volcano as described
for the Towada volcanic ash soils (Shoji et al., 1993a).
Wetness of volcanic ash soils also contributes greatly
to the accumulation of soil organic matter (SOM): low
SOM content at dry sites and high SOM content at
wet sites. Thus there are notable differences in thenatural N supply and amount of plant-available water
between the two areas.
Precision agriculture will be attractive for site specific management of large-scale fields of volcanic ash
soils with high spatial variability. It is useful forbalancing nutrient supply and demand, and for managing pesticides, water and tillage. The precise
amount of fertilizer and other agricultural inputs canbe determined by employing combined geographicalinformation and global positioning systems(GIS–GPS), and applied to the fields bycomputer-controlled machinery.
Site-specific management of phosphorus andpotassium will be more accurate in volcanic ash soils,
because the testing for plant-available forms of theseelements is reasonably reliable. However, testing forplant-available nitrogen is highly difficult because thenatural nitrogen supply contains both mineralized
nitrogen and mineral nitrogen and is considerablychangeable. Therefore, programmed fertilization using
high performance controlled-release fertilizers will bevery helpful for intensive agriculture on volcanic ash
soils.
Programmed fertilization using controlled releasefertilizer (CRFs)
Nitrogen is a fertilizer element that most strongly
determines yield, quality and safety of crops morethan any other element. However, this element also
contributes greatly to environmental degradation if

Environmental and Agricultural Significance of Volcanic Ash Soils

applied excessively or improperly.
Thus programmed fertilization using high performance controlled release N fertilizer can efficiently enhance thebeneficial effects and improve the defects of nitrogen
fertilization.
Recently, the total production of nitrogen fertilizers
in Japan has decreased: the production in 2000 was
90.0% of that in 1995. In contrast, the production ofcoated nitrogen fertilizer (mainly polymer-coatedurea) has been on a continuously increasing trend
since 1983 and the ratio of 2000/1995 production is136.8% (Nihon Kaseihiryo Kyokai, 2002). It is wellknown in Japan that coated nitrogen fertilizers havecontributed to development of new agro-technologies
for intensive agriculture.
A variety of controlled-release nitrogen fertilizers
are marketed in Japan (Koshino, 2001). However,thermoplastic polyolefin-coated fertilizers (POCFs)
such as the polyolefin coated urea named “MEISTER”
appear to be the best from the viewpoint of accuracyof controlled release. They include two groups ofrelease patterns: linear and sigmoidal as shown in
Fig. 6. By selecting suitable formulations, it is easy
to design fertilization programs that best meet thenitrogen demand of various crops. The release of thenutrient elements in POCFs is primarily determinedby temperature, so their release patterns can be easily
obtained by computer simulation (Shoji and Takahashi,1999).
Programmed fertilization and single basal application
Conventional nitrogen fertilizers mostly show
short duration of nitrogen supply under humid climate
and paddy conditions, and low nitrogen use efficiency.
Thus, split application is commonly practiced to improve these drawbacks. On the other hand, correctly
programmed fertilization using CRFs is conducted by

Cumulative N release %100

Best site placement
Since CRFs can continuously supply crops withnutrient elements little by little, meeting crops’ nutrient demands, they can be placed by one application to
the best site in the soil without the danger of fertilizer

140

100

180
80

270

60
40
20
0

SS100
S40 S60 S80 S100 S120 S160

S200

50

250

80
60
40
20
0

0

50

100

150

200

250

Days after application

Linear release group
Fig. 6

single basal application for most crops in Japan.
For example, paddy rice has two peaks of nitrogen
demand: one comes at the intense tillering stage earlyin the growing season and the other, at the young
panicle formation stage in the mid growing season.
As presented in Fig 7, computer simulation can selecta short linear formulation of POC urea (MEISTER)
for the first peak, and a long sigmoidal formulation of
POC urea (MEISTER) for the second peak. If there
is a need to realize rapid establishment and good early
growth for transplanted paddy rice, it is recommended
to apply basally a blend including a conventional
fertilizer and two CRFs (a short linear formulation anda long sigmoidal formulation).
Single basal
application using CRF blends is extensively practiced
for many crops even if their growing season is very
long. For example, the recommended N fertilization
for tea plants in Kumamoto Prefecture is eight split
applications using conventional N fertilizers and thetotal amount of applied N is 700 kg per ha per year.
In contrast the innovative fertilization uses a blend ofpolyolefin-coated urea formulations (a short linear
formulation and three long sigmoidal formulations of
MEISTER) and is practiced by one-time application inearly September as shown in Fig. 8. It can continuously supply N to tea plants to enhance the quality andyield of tea leaves and can significantly increase N use
efficiency. Therefore, its N rate is considerably
reduced compared with the conventional N rate, contributing to control of fertilizer pollution (Shoji andHigashi, 1999).

Cumulative N release %30 40 50 70

100

131

0

100

150

200

Days after application

Sigmoidal release group

Nitrogen release from polyolefin coated urea (international name: MEISTER; domestic name: LP-cote) in water at
25°C (courtesy of Chisso Corporation, 2002).
N.B.: Both groups have many formulations described using numbers. Each number shows number of days required torelease 80% of the nutrient content.

132

S. SHOJI and T. TAKAHASHI

Fig. 7

Conceptual presentation of the N supply pattern of programmed fertilization of paddy rice by single basal
application.
N.B.: easily soluble N, 20%; short linear MEISTER N, 40%; long sigmoidal MEISTER N, 40%.

Month
Fig. 8Sep.

Oct. Nov. Dec.

Jan.

Feb. Mar. Apr. May

Jun.

Jul.

Aug.

Nitrogen supply pattern of a polyolefin coated urea (MEISTER) blend for tea plants in Kumamoto Prefecture.
Time of application was September 1 (courtesy of Chisso Corporation, 2002).
N.B.: Nitrogen supply is maximized in the early spring and early autumn to enhance the yield and quality of tea
leaves.

injury to the crops. One example is single basal
nursery fertilization of paddy rice that employs asigmoidal
polyolefincoatedurea
called“Naebako-makase” (a special formulation of
MEISTER). It can supply fertilizer N meeting theplants needs during the whole growing season. This
unique fertilization method developed by Kaneta et al.
(1994) is called “co-situs sheet placement” by which
all the N fertilizer “Naebako-makase” is applied on or
beneath the rice seed layer in a nursery box. It could
increase nitrogen use efficiency by approximately
100% compared to conventional nitrogen use
efficiency (N use efficiency by innovative fertilizationis 80%). The innovative fertilization proposed by
Kaneta et al. (1994) has notably stimulated thecreation of new fertilization methods for other crops
as well in Japan.
Innovative agro-technologies and their contributions
to improving the agro-environment
Various agro-technologies have been developed bymaking effective use of high quality CRFs. They
include no-till transplanting culture with single basal
nursery fertilization, no-till direct seeding crop culture
by single basal fertilization, single basal fertilization
by deep placement for soybeans, and multiple plantings of horticultural crops by one-time fertilization.
The new agro-technologies using CRFs can contribute
greatly to mitigation of water, atmospheric and biological environmental problems related to intensive

Environmental and Agricultural Significance of Volcanic Ash Soils

agriculture (Shoji and Minami, 2002).
The advantages of high performance polymer-coated N fertilizers useful for intensive
agriculture are summarized as follows:
1) The release control is highly accurate andcomputer simulated as a function of temperature,enabling preparation of rational fertilization programs,2) Polyolefin coated urea contains 40% or more
N and has a variety of linear and sigmoidal formulations, being most suitable to production of favorable
blended fertilizers.
3) Single basal application can be practiced bybest site placement even for multiple plantings,
4) Nitrogen use efficiency can be remarkably enhanced by innovative fertilization. Environmental
degradation due to intensive fertilizer application canbe minimized by maximizing fertilizer efficiency(Shoji and Minami, 2002), and
5) Enhancing the quality and safety of farm
products by adjusting the N rate and ratio of mineralforms: decreasing the concentrations of nitrate andoxalic acid and increasing the concentrations of sugars,
amino acids and ascorbic acid in some horticultural
plants (Shoji and Higashi, 1999).
As already described, nowadays volcanic ash soils
in Japan are mostly utilized for intensive horticultural
cropping, so innovative agro-technologies using highperformance CRFs are highly useful for sustaining the
volcanic ash soils.

Acknowledgements
Valuable information and suggestions on ourmanuscript were provided by many people: H. Ota,
M. Saito and S. Tsuyuzaki (restoration of vegetationand soil environments), M. Yokohari (amenity),
Y. Inoue and H. Kubotera (pedogenesis and soil
properties), M. Kuwahata and S. Narita (archaeology),
T. Sase (paleovegetation), T. Iwase and H. Mochida(croppingsystems),andA. Sakamoto(controlled-release fertilizer). We wish to express
hearty thanks to these people described above.
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(Received 2 September 2002, Accepted 10 October 2002)