schafer 2000 soil and tillage research

7/30/2019 Schafer 2000 Soil and Tillage Research

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The soil and climate characterisation of benchmark sites forlowland rice-based cropping systems research in

the Philippines and Indonesia

B.M. Schafera, G. Kirchhofb,*

a

School of Agriculture and Horticulture, The University of Queensland, Gatton, Qld 4343, AustraliabSchool of Land and Food Sciences, The University of Queensland, St Lucia, Brisbane, Qld 4072, Australia

Abstract

Soil morphological, physical, chemical and mineralogical properties are described at ve locations in major rice (Oryza

sativa L.) growing areas of the Philippines (two sites) and in Indonesia (three sites) which were selected for lowland rice-based

cropping systems research. The data were used to classify the soils into the local soil series, soil taxonomy and The Australian

Soil Classication systems. These data were intended to facilitate transfer of knowledge of improved farming systems

technology to other lowland rice growing areas in the regions. The soils were classied as Andsisols, Inceptisols and Vertisols,

and were characterised by clay contents ranging from 370 to 870 g kg1 and cation exchange values ranging between 17 and

68 cmol (p) kg1

for whole soil. pH values were neutral to mildly alkaline. Land surface and root zone attributes werequalitatively evaluated for limitations to post-rice crop production by interpretation of modied surface and sub-soil properties

associated with rice production. Leakiness of bunds was also examined and mainly attributed to biological activity and for the

development of drainage channels. Climatic data are presented for each of the ve sites and the characteristics for potential

rainfall incidence are given for the post-rice dry season crop period. The soil sites selected have a range of properties which

are deemed to represent large areas of soils used for rice production in these two countries.# 2000 Elsevier Science B.V. All

rights reserved.

Keywords: Rice soils; Pedology; Soil properties; Climate

1. Introduction

Soils used for lowland rice-based cropping systems

in Indonesia and the Philippines are characterised by

high surface clay content and the fact that they are

puddled to aid water retention during the inundation

period of the rice crop cycle. Following a rice crop, the

potential to use sub-surface soil water for upland crop

production entails amelioration of the adverse effects

of puddling on surface soils. For successful cropestablishment the rainfall incidence following rice

is critical. Consequently soilclimate constraints are

a major consideration at the early stage of the dry

season crop cycle and seed bed preparation together

with timing of the establishment phase is critical

(Rahmianna et al., 1996).

Two sites in the Philippines and three sites in

Indonesia were selected as benchmark sites for an

international collaborative project to investigate

soil management strategies to increase yields of dry

season crops following rice. Components of these

Soil & Tillage Research 56 (2000) 1535

* Corresponding author. Present address: NSW Agriculture, PMB

944, Tamworth NSW 2340, Australia. Tel.: 61-2-67-63-1147;

fax: 61-2-67-63-1222.

E-mail address: [email protected] (G. Kirchhof).

0167-1987/00/$ see front matter # 2000 Elsevier Science B.V. All rights reserved.

PII: S 0 1 6 7 - 1 9 8 7 ( 0 0 ) 0 0 1 2 0 - 3


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management strategies include various soil tillage

practices, application of mulch and amendments

and agronomic practices.

Comparison across the ve sites requires detailedcharacterisation of soil properties using standard

description terminology and analytical methods for

classication, according to soil taxonomy (Soil Survey

Staff, 1994). Characterisation is also required to facil-

itate transfer of research outcomes to other rice

growing regions in terms of the combined effects

of soilclimate attributes and tillage treatments on

potential crop establishment, growth and yield of

dry season crops. This paper provides detailed

descriptions of the soils and climate at the ve experi-

mental sites. This should avoid the use of incompletesoil and climate descriptions in the following papers

from the project.

In the Philippines the soils of the Bulacan Province

have been described, mapped and classied in detail

(Soil Survey Division, 1987). Soil description and

analytical characteristics were provided for soil near

the site at Manaoag in the Pangasinan Province.

However the data were not correlated with soils in

the region and terminology used was insufcient for

classication.

The soils of East Java have been variously describedand classied at the regional level but limited data

were available for the selected experimental sites. In

South Sulawesi, the soils of the Maros Agricultural

Research Station have been described (Ali and Sawijo,

1982) although the experimental site was outside of

the area surveyed.

The climate in the Philippines is governed by

northeast and southwest monsoon air streams. The

northwest monsoon originates in the cold Asiatic

winter anticyclone and produces a distinct dry season

from around October to May. The southwest monsoonoriginates as an Indian Ocean anticyclone during the

southern hemisphere winter. It usually commences

in early May, reaches its maximum inuence in

August and abates in October. Monsoonal rains can

occur as early as April and May and persist until

November.

The Philippines is located in a region which is

recognised as having the greatest frequency of tropical

cyclones (typhoons) in the world (Flores and Balagot,

1969). They produce rainfall between May and

December with a mean monthly frequency of greater

than 0.5 throughout the year, but generally less than

1.0 between January and May.

The climate in Indonesia is dominated by monsoo-

nal air streams which are at opposite times of the yearto those in the Philippines. Rainfall in Java is largely

affected by the position of the intertropical conver-

gence zone which passes through twice annually. It is

inuenced by the mountainous areas of Borneo and

Sumatra (Sukanto, 1969). Although the wet and dry

seasons are distinct, a moderate amount of rainfall

occurs during the dry season which results in rainfall

throughout the year. In southeast Sulawesi, a distinct

dry season occurs but wet season rainfall is consider-

ably higher than that of Java due to the inuence of the

landmasses and mountains of Borneo. Compared tothe Philippines, Indonesia has a very low incidence of

tropical cyclones.

2. Methods

Soil pits were hand dug to a minimum depth of

1.5 m to expose a vertical face of soil within a rice

paddy and also to expose a vertical face of the

associated bund. The proles were described using

terminology proposed by McDonald et al. (1984) withminor modication by the use of consistence terms

proposed by Soil Survey Staff (1951). This modica-

tion was made to facilitate communication with the

professional workers in the two countries. The sites

and prole exposures were photographed to provide avisual record.

Soils were sampled for laboratory analysis by tak-

ing bulk samples from the designated horizons. These

samples were analysed by the CSIRO Laboratories

located in Canberra and Adelaide, Australia (Ring-

rose-Voase et al., 1996). Chemical methods follow theAustralian Laboratory Handbook of Soil and Water

Chemical Methods (Rayment and Higginson, 1992).

Particle size analysis was determined by the sedigraph

method (Hutka and Ashton, 1995) and mineralogy of

the clay fraction was analysed semi-quantitatively by

X-ray diffraction (Raven, 1995).

The soils were classied according to soil taxon-

omy (Soil Survey Staff, 1994) and The Australian Soil

Classication (Isbell, 1996). Soil survey reports and

local information gained from professional workers

associated with the program were used to identify soils

16 B.M. Schafer, G. Kirchhof / Soil & Tillage Research 56 (2000) 1535


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classied at the series level and to assist in the other

classication systems.

3. Soil descriptions

3.1. Benchmark Site 1, San Ildefonso

Location the Philippines, Luzon Island, Bu-

lacan Province, San Ildefonso (see

Fig. 1), Barangay Buenasita, Cen-

tral Soil and Water Resources

Research Station

Classification soil series: Mahipon series; soil

taxonomy: Ustic Epiaquert andAustralian Classification: Endocal-

careous, Mottled, Epipedal and

Aquic Vertosol

Topography gently sloping (38) to undulating

relief; site component, slightly

dissected lower piedmont footslope

fringing a closed depression

Parent material colluvium derived from sandstone,

shale and limestone

Drainage surface: well drained and internal:

impeded and slowly permeableLand use rice-based cropping

Prole morphology

Ap1, (mixed, puddled) 013 cm, dark yellowishbrown (10 YR 4/4), dark greyish brown (10 YR 4/2

moist), very dark grey (10 YR 4/1), dark brown (7.5

YR 4/4) (dominant) mixed, gravelly, fine sandy clay;

moderate medium, 510 mm, angular blocky; rough

ped fabric; dry extremely hard, moist firm, wet sticky

and plastic. Common fine roots with rusty mottlingon walls of very fine macropores (root channels).

2530%, 14 mm, sub-rounded, cemented ferro-

manganiferous nodules. Occasional 7 cm diameter

sub-rounded pebbles of dolerite. Field pH 6.0.

Clear discontinuous wavy with tongued pockets of

gravelly fine sandy clay to: A12, 1327 cm, light

brownish grey (10 YR 6/2 moist) with dark grey

(10 YR 3/1), dark greyish brown (10 YR 4/2) many

medium distinct mottles; gravelly fine sandy clay;

moderate, 510 mm, angular blocky; rough ped

fabric; dry extremely hard, moist firm, wet sticky

and plastic. Few very fine macropores. 510% soft to

hard ferro-manganiferous nodules. Occasional sub-

angular quartz and feldspar crystals. Field pH 6.0.

Discontinuous wavy to: B21, (Mn) 2767 cm, lightolive grey (5 Y 6/2 moist) with many, medium

distinct brownish yellow (10 YR 6/6 moist)

mottles; gravelly medium clay; strong, 20

50 mm, lenticular with intersecting slickensides

parting to 1050 mm, angular blocky and 25 mm

lenticular; smooth ped fabric; dry hard, moist firm,

wet sticky and plastic. Occasional 25 mm dia-

meter quartz gravels with translucent iron coatings.

Common very fine pores and roots. Field pH 6.5.

Gradual wavy to: B22, (Ca) 6797 cm, light olive

grey (5 Y 6/2 moist) with many medium distinctbrownish yellow (10 YR 6/6) mottles; medium

clay; strong, 2050 mm lenticular with intersect-

ing (30608) slickensides parting to 1050 mm

angular blocky and 25 mm lenticular; smooth ped

fabric; dry hard, moist firm, wet, very sticky and

plastic. Field pH 8.0. 5%, sub-rounded, soft CaCO3nodules. Occasional black manganese nodules.

Gradual wavy to: B23, 97140 cm, light olive grey

(5 Y 6/2 moist) medium clay; strong, 25 mm

lenticular with slickensides on compound ped

surfaces; smooth ped fabric; moist friable, wetsticky and very plastic. Occasional black sub-

rounded manganese nodules. Field pH 8.0.

Clear to: C, 140150 cm (continuing), weathered

shale.

3.2. Benchmark Site 2, Manaoag

Location the Philippines, Luzon Island, Pan-

gasinan Province, Manaoag (see

Fig. 2), Barangay Calmay and

farmers fieldClassification soil series: San Manuel silty clay

loam; soil taxonomy: Typic Ustro-

pept and Australian Classification:

Haplic, Eutrophic, Grey and Der-

mosol

Topography backslope (


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Fig. 1. Benchmark Site 1, San Ildefonso, Ustic Epiaquert.



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Fig. 2. Benchmark Site 2, Manaoag, Typic Ustropept.

B.M. Schafer, G. Kirchhof / Soil & Tillage Research 56 (2000) 1535 19


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Prole morphology

Ap1, 011 cm, very dark greyish brown (10 YR 3/

2 moist) silty clay; coarse polyhedral with

conchoidal faces (primary), breaking to compound

prismatic (secondary) breaking to strong, 25 cm

polyhedral (tertiary); rough ped fabric; dry ex-

tremely hard, moist very firm, wet sticky and

plastic. Common fine roots. Field pH 6.5.

Abrupt smooth to: Ap2, 1138 cm, dark greyish

brown (10 YR 4/2 moist) silty clay; coarse

polyhedral with conchoidal faces breaking to

compound prismatic, further breaking to strong,

25 cm polyhedral; rough ped fabric; dry extre-

mely hard, moist very firm, wet stick and plastic.Common fine roots. Field pH 6.5.

Arbitrary clear smooth to: A13, 3869 cm, dark

greyish brown (10 YR 4/2) silty medium clay;

compound prismatic breaking to moderate fine 2

5 mm polyhedral with well developed organans,

rough ped fabric; dry hard, moist friable, wet

sticky and plastic. Occasional roots. Field pH 7.0.

Arbitrary clear smooth to: A14, 69104 cm, dark

greyish brown (10 YR 4/2 moist) medium clay,

compound prismatic 25 cm breaking to medium

37 mm polyhedral with well developed organans;rough ped fabric; dry extremely hard, moist friable,

wet sticky and plastic. Occasional roots. Field pH

7.5.

Arbitrary clear to: AC1, 104117 cm, very dark

greyish brown (10 YR 3/2) common medium

distinct dark yellowish brown (10 YR 4/6) mottles;

silty loam; compound prismatic breaking to

medium, 37 mm polyhedral; rough ped fabric;

dry hard, moist friable, wet sticky and plastic.

Occasional roots. Field pH 7.5.

Arbitrary to: AC2, 117160 cm (continuing), darkyellowish brown (10 YR 4/6) many medium

distinct, very dark greyish brown, mottles (organ-

ic); silty clay loam; compound prismatic breaking

to medium 37 mm, polyhedral; rough ped fabric;

dry extremely hard, moist firm, wet sticky and

plastic. Field pH 7.5.

3.3. Benchmark Site 3, Ngale

Location Indonesia, East Java, Ngawi,

Ngale Experiment Station of the

Research Institute for Legume and

Tuber Crops (RILET) (see Fig. 3)

and Malang (formerly MARIF)

Classification soil series: unnamed; soil taxon-omy: Chromic Epiaquert and Aus-

tralian Classification: Haplic,

Epipedal and Aquic VertosolTopography almost flat (


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Fig. 3. Benchmark Site 3, Ngale, Chromic Epiaquert.



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3.4. Benchmark Site 4, Jambegede

Location Indonesia, East Java, Jambegede

(se e Fig. 4), 20 km south of Malang at the Research Institute

for Legume and Tuber Crops (RI-

LET) and Malang (formerly MAR-

IF)

Classification soil series: unnamed; soil taxon-

omy: Anthraquic Hapludand and

Australian Classification: Mottled,

Sodic, Eutrophic and Black, Der-

mosol

Topography levee backslope (1.58)

Parent material weathered andesitic tuff and ashDrainage surface: seasonal flooding and

internal: moderately well drained,

moderately permeable

Land use rice-based cropping systems

Prole morphology

Ap, (puddled) 018 cm, very dark grey (10 YR 3/1

moist) admixed with partly humified crop residue:

dark yellowish brown (10 YR 4/6) mottling at

admixture face; light clay; blocks 1015 cm

cracking coincidentally with plant row distribution.Blocks break into 57 mm sub-angular with rusty

brown cutans. Some evidence of platiness 25 cm

width at base of puddling depth. Earthy fabric;

moist friable, wet sticky and plastic. Common

roots. Field pH 77.5.

Clear smooth to: A12, 1845 cm, very dark grey

(10 YR 3/1 moist) common medium faint yellow-

ish brown (10 YR 5/8) mottles; light to mediumclay; strong coarse, 2040 mm sub-angular blocky

with incipient conchoidal faces on upper surfaces;

rough ped fabric and macropores; moist friable to

firm. Few reddish brown (2.5 YR 4/6) earthy scoria

to 4 cm diameter. Field pH 88.5.

Fig. 4. Benchmark Site 4, Jambegede, Anthraquic Hapludand.



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Diffuse smooth to: A13, 4562 cm, very dark grey

(10 YR 3/2 moist) common coarse distinct yellow-

ish red mottle, medium clay; coarse angular blocky

to strong polyhedral (57 mm), rough ped fabricand common macropores; moist friable to firm.

Field pH 77.5. Few roots. Occasional (


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Fig. 5. Benchmark Site 5, Maros, Aeric Tropaquept.



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probably due to wetting and drying cycles of the

surface soil which inundates during wet seasons.

Current cropping practices have probably accelerated

the process of nodule formation. Layering evident inthe Ap horizon was deemed to be due to puddling.

Tongues of Ap horizon soil material in A12 horizon

were interpreted as inll wash of surface material into

vertical cracks following saturation and dispersion of

soil material with low liquid limits. Churning of

material in the upper part of the prole was evidenced

by the presence of up to 50 cm diameter pockets of

contrasting sandy textured soil material which indi-

cated that pedoturbation had occurred during pedi-

ment development. The boundary of the pocket was

coincidental with major slickenside surfaces whichindicated considerable internal mixing of surface and

sub-soil materials. Vertical cracks up to 1 cm wide and

at mean intervals of 50 cm were evident to 150 cm

depth.

Soil properties of the bund were found to be similar

to the Ap horizon. The position of the bunds is not

permanently located and they are reformed on a

seasonal basis. This is probably due to the high

shrinkswell property of the clay which would cause

bund failure with decreasing water content and con-

comitant soil shrinkage.The Typic Ustropept soil located at Manaoag (Site

2) was observed to have well developed macropores

throughout the prole which appeared to be old root

channels. Few, large, vertical cracks 1 cm wide to 1 m

depth and 1 m spacing were observed and may be due

to wetting and drying following compaction. Compac-

tion is evident in Ap horizons by the presence of

domed conchoidal faces on upper surfaces of com-

pound peds. Well developed organans on surfaces of

peds indicated organic matter distribution to 1 m depth

in the prole.At Ngale (Site 3) the bund associated with the

Chromic Epiaquert prole was similar to soil material

described for Ap1 except that the fabric was classed as

earthy due to the presence of well formed macropores

with rust coloured coatings which appeared to be old

root channels. In the B22 horizon below the associated

bund, 11.5 cm diameter, preferred drainage channels

were observed inlled with dark grey (5 Y 4/1 moist)

clay which indicated reduced conditions. These chan-

nels appeared to have been formed by macrofauna

(crabs). A water table at 160 cm coincided with

accumulation of calcium carbonate. Dominant grey

colours suggested that anaerobic conditions persist at

least seasonally. Roots were evident to 1.5 m and were

identied as rice plant roots. Moisture contentthroughout did not appear to be uniform and where

structure was more strongly developed the soil

appeared to be better drained. Patches of rusty brown

mottles in the upper B21 were associated with con-

centrations of roots in more strongly structured soil

and associated with soil cloddiness.

The Anthraquic Hapludand described at Jambegede

(Site 4) contained common worm castes 3 mm in

diameter which occupy up to 20% by volume at depth.

Surfaces of vughs (25 mm diameter) are convoluted

suggesting preferred drainage channels are developedin some root channels. pH increase in the A12 horizon

together with conchoidal face development indicated

restricted drainage in the puddled zone. The bund

associated with the prole was described as a very

dark greyish brown (10 YR 3/2) clay loam. Rat

burrows were evident and inlled with plant and soil

material. Below the bund, soil material was found to

be compacted and similar to the Ap horizon. Macro-

porosity was well developed throughout the prole

due to root and earthworm channels. At Maros (Site 5)

the mammilated walls of vughs ranging in size fromless than 1 to 7 mm diameter were coated with grey

oriented silt. Macroporosity was well developed

throughout B2 horizons. A brownish black manganese

patina on compound ped surfaces in the Ap1 (puddled)

indicated poor drainage. In the Ap3 (compacted)

cutans on compound peds were described as having

a smooth ped fabric indicating a drainage restriction.

Rough ped fabric is evident on primary units. Rapid

oxidation on exposure also indicated strong anaerobic

conditions.

5. Soil prole analytical properties

The soils used for experimentation have more than

400 g kg1 clay (


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distribution over depth with clay content increasing

from 400 g kg1 at the surface to 750 g kg1 at depth.

The clay content of the soil at Jambegede increases

with depth from 450 g kg1 near the surface to

600 g kg1 at depth, with a corresponding decrease

in sand content.

The Chromic Epiaquert (Site 3) is a heavy clay soil

with clay content increasing from 740 g kg1 in the

surface to 880 g kg1 at depth. The Typic Ustropept

(Site 2) and Aeric Tropaquept (Site 5) have similar

particle size distributions with 450500 g kg1 clay

throughout. Sand content increases with depth from

30 g kg1 near the surface to 100 g kg1 at Site 2, and

200 g kg1 at Site 5. This characteristic of these two

proles suggests that the soil material is of alluvial

origin.

Table 1

Particle size distributions using USDA clay, silt and sand fractions

Depth (cm) g kg1 in texture class (mm)

Clay (


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Chemicalandmineralogicalanalyses(Tables2and3)

showthatthesoilsareneutralpHwiththeprolesatSite

1 and Site 5 being mildly acid in their surface horizons.

Cation exchange capacities vary from 20 cmol (p)

kg1 in the soil at Site 5 to nearly 70 cmol() kg1 in

the soil at Site 3. The exchange complexes are domi-

nated by calcium and magnesium and show no imbal-

ance of cations which would limit plant growth. These

values are supported by the clay species identication

which show a predominance of kaolinite and smectite.

The soils at Sites 2 and 5 also contain signicant

proportions of vermiculite and illite, respectively. The

clay species in the prole at Site 3 was predominantly

smectite which is reected in the high cation exchange

capacity values throughout. In contrast, the clay frac-

tion of the prole at Site 2 contained 63% smectite in

the surface which decreased with depth and is replaced

by kaolinite. This suggests that the prole is layered

with more recent alluvial depositions having higher

smectite clay contents.

Table 2

Chemical properties

Depth (cm) Organic

carbon (g kg1

)

pH EC (1:5 extract

dS m1

)

Exchangeable cations CEC

Ca (cmol

(p) kg1)

Mg (cmol

(p) kg1)

Na (cmol

(p) kg1)

K (cmol

(p) kg1)

San Ildefonso

011 11.65 6.54 0.090 11.5 7.7 0.58 0.22 21.4

1130 4.14 7.35 0.062 12.7 9.5 0.87 0.11 23.4

30, Ap Ta 4.29 7.42 0.059 9.1 7.3 0.76 0.00 17.4

3070 2.56 7.99 0.069 15.2 12.6 1.05 0.00 28.2

70110 1.28 7.80 0.140 27.3 22.3 1.29 0.00 49.1

Manaoag

011 11.30 7.71 0.112 36.0 10.6 0.42 1.02 43.6

1138 9.83 7.61 0.104 41.3 9.7 0.40 1.16 52.8

3869 8.29 7.55 0.120 42.1 7.5 0.34 0.70 49.269104 6.38 7.64 0.101 33.5 4.4 0.31 1.85 40.7

104117 4.77 7.76 0.094 31.5 4.5 0.25 1.26 42.3

117160 4.84 7.77 0.092 26.7 5.0 0.35 0.38 33.3

Jambegede

018 11.67 7.60 0.097 9.6 6.7 0.27 1.74 18.6

2040 7.84 7.23 0.178 9.1 6.9 0.52 1.48 17.2

4060 4.67 7.40 0.079 8.1 5.7 0.80 2.71 17.6

6080 4.23 7.56 0.073 7.4 5.0 0.76 2.94 16.6

80160 4.04 6.98 0.070 7.1 5.0 0.77 4.00 16.5

Ngale

014 14.32 7.05 0.103 52.4 14.5 0.32 0.89 69.5

1434 11.47 7.20 0.111 51.5 14.6 0.35 0.55 68.73454 7.48 7.21 0.108 51.3 13.8 0.39 0.31 62.6

5478 6.46 7.01 0.064 57.4 16.1 0.44 0.19 74.2

78110 5.64 7.64 0.060 52.4 15.3 0.42 0.31 68.0

Maros

012 16.32 4.88 0.106 5.7 4.8 0.20 1.56 15.6

1214 15.06 5.06 0.068 6.0 5.1 0.27 0.86 14.9

1422 6.88 6.25 0.059 9.7 7.9 0.25 0.79 17.6

2241 6.15 6.63 0.054 10.3 8.4 0.33 0.54 19.9

4171 2.67 6.75 0.066 11.9 9.3 0.49 1.01 22.2

71110 2.30 6.90 0.062 11.5 9.2 0.47 1.20 22.9

110150 1.97 6.97 0.057 12.1 10.1 0.43 1.67 24.9

a

Tongues of Ap material at 30 cm depth.



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The smectite content of the soil prole at Site 1 is

similar to that at Site 2 near the surface but remains

constant with depth. However the increase in percen-

tage of clay with depth results in the swelling clay

component increasing from 26 to 46%. In contrast, the

clay fraction in the surface soil at Site 4 contained 33%

smectite which decreased to 12% at depth.The clayfraction in the soil at Site 5 contained 20% smectite

near the surface which increased to 30% at depth. The

relatively constant clay content in the soil results in the

smectite content of the clay fraction only changing

marginally from 9 to 15%.

6. Potential soil limitations for plant growth

Soil properties limiting plant growth were inter-

preted from the qualitative descriptions obtained for

each site and prole (Table 4). Diagnostic pedological

features were used to assess the potential of the soils

for dry season crops which require soil depths greater

than that provided by the puddled surface soil layers.

The interpretations were based on the general edaphic

conditions and do not account for the specic crop

requirements. The term hard-setting is used to denethe soil surface condition created by puddling and

drying.

7. Climate

The characteristics of the climate at each site are

presented in Figs. 610. Limited data prevented

detailed analysis in relation to crop risk analysis

based on soilclimatic probability relationships and

Table 3

Mineralogy of the clay fraction

Site depth

(cm)

Mineralogical composition (% of


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Table 4

Qualitative descriptions of each site and soil prole

Soils Land surface limitations Limitations in root zone

Seasonal

flooding

Slope Surface

condition

Internal

drainage

Permeability Effective

depth (cm)

Depth

DSWT

Philippines

Ustic Epiaquert

(San Ildefonso)

128 Hard-setting Poor, strongly mottled;

Fe, Mn concentrations

Slow to

very slow

100150 >50

Typic Ustropept

(Manaoag)

None 100

Indonesia

Chromic Epiaquert

(Ngale)

Seasonal


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only average values could be obtained to indicate

potential rainfall during the post-rice period. Future

work to establish probabilities for dry season crop

establishment success rate would be a benet to

extrapolate research ndings of the project to other

regions. The probabilities of daily rainfall exceeding

different values are calculated from the available long

term average daily rainfall events.

The average annual rainfall at San Ildefonso Vista

(Site 1) is 1986 mm. Long term daily average rainfall

and probability is given in Fig. 6. The wet season

lasts from around mid-May through November

with highly variable daily rainfall events. Post-rice

crops are usually sown between early December

and late February which is at the end of the wet

season. In contrast to the abrupt change from the

Fig. 6. Medium term average daily rainfall and probability for rainfall (1988 to 1995) at San Ildefonso.



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dry to wet season, the change from wet to dry is

relatively gradual which is important for dry season

crop establishment. Although the probability for

rainfall remains above 10% throughout the dry

season, the chances of crop damage from high inten-

sity storms are minimal. Occasional typhoon activity

during this otherwise dry period may occur in some

years.

Fig. 7. Recent average daily rainfall (1992 to 1994) at Manaoag, Pangasinan and probability for rainfall combined from 3 sites near Manaoag

over 9 years.



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Average annual rainfall recorded at Manaoag (Site

2) is 1486 mm. The dry season extends from about

mid-October through May (Fig. 7). Compared to the

San Ildefonso site, the transition from wet to dry

season is more abrupt which can be explained by

the lower probability of rainfall throughout the year.

The wet season tends to commence with relatively

large erratic rainfall events commencing in March

which become more regular in occurrence by May

with the incidence of moderate rain (1050 mm per

day). These rainfall events make the Manaoag area

more suitable for post-rice cropping.

Average annual rainfall at Ngale (Site 3) is

2179 mm. The wet season occurs during the period

between October and April and is followed by a

moderately wet dry season (Fig. 8). The transition

Fig. 8. Long term average daily rainfall and probability for rainfall (1981 to 1995) at Ngale.



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from wet to dry season is gradual with a high prob-

ability of effective rainfall for post-rice plant estab-

lishment and growth. Compared to the sites in the

Philippines, post-rice crops are established earlier and

at the end of the wet season. This is made possible due

to the lower frequency of tropical cyclones and more

reliable rainfall events. Average annual rainfall at

Jambegede (Site 4) is 2202 mm. The characteristics

of rainfall distribution (Fig. 9) are regarded as being

comparable to those at Ngale.

Average annual rainfall at Maros (Site 5) is

3085 mm. Compared to East Java, the wet season is

more intense with probabilities for daily rainfall

events approaching 90% (Fig. 10). The transition from

wet to dry season is abrupt although rainfall peaks in

January and declines to a minimum in July. The

Fig. 9. Long term average daily rainfall and probability for rainfall (1983 to 1995) at Jambegede.



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transition from wet to dry season occurs during the

period from April to May and is comparable to the

sites in East Java.

Acknowledgements

This work was funded by the Australian Centre for

International Agricultural Research.

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