009/06 VIE Six-monthly Report- April 2008
Attachment 1 009/06 VIE: Improving capability of provincial extensionists for
assessing soil constraints to sustainable production through the use of the
SCAMP decision support system.
Major Cropping Soils and Soil Constraints to Productivity
of Major Upland Crops Grown by Smallholders

I. Gia Lai Province
PW Moody
A
and Phan Thi Cong
B A
Queensland Department of Natural Resources and Water, Indooroopilly, Qld 4068,
Australia
B
Institute of Agricultural Sciences of Southern Vietnam, Ho Chi Minh City,

that occur in Gia Lai Province are presented in Table 1.

Table 1. Areal extent of Soil Groups in Gia Lai Province.
Source: Le Trung Lap, 2000.

Soil Groups Area (ha) Proportion (%)
Chromic and Haplic Acrisols
Acric,Humic and Vetic Ferralsols
756,433 49
Dystric and Gleyic Arenosols
Luvisols
364,638 23
Leptosols 164,752 11
Alumic, Hyperdystric and Chromic Acrisols
Acric, humic and Vetic Ferralsols
90,481 6
Mollic Fluvisols
Luvic and Fluvic Phaeozems
Cambisols
64,218 4
Dystric Gleysols 16,774 1
Others 92,275 6
TOTAL 1,549,571
3
The land forms of Gia Lai have been classified (Berding et al., 1999) as:
 Hills and low mountains,
 Basaltic plateaus,

acidity (H +Al), ECEC, pH buffer capacity (calculated) From these data, SCAMP (Moody and Phan Thi Cong, 2008) was used to
identify the constraints of these two major soil groups to sustainable production
(Table 3). 4
Table 3. SCAMP descriptors for 14 Ferralsols and 16 Acrisols of Gia Lai
Province, Vietnam. Number of sites with the attribute is in parentheses.

Attribute Ferralsols Acrisols
Texture L (9); LC (5) L (10); C (2); LS (4)
Erosion hazard er(slight) (9), er(moderate) (2),
er(high) (2), er(very high) (1),
er(slight) (3); er(moderate) (2);
er(high) (6); er(very high) (3);
er(extreme) (2)
Water pathway drainage (7);
drainage + runoff (7)
drainage (8);
drainage + runoff (5); runoff (3)
Acidity surface a (14); subsurface a (12) surface a (2); subsurface a (1)
Acidification hazard ar(low) (14) ar(low) (2); ar(moderate) (12);
ar(high) (2)
Low nutrient retention e (12) e (3)
High P fixation i (14)
Low organic C om (2)
Low K reserves surface k (1); subsurface k (1) surface k (1); subsurface k (7)

for sustainable productivity:
a: Acid tolerant crops should be grown as a short term response to this constraint.
For long term sustainability, a liming program should be commenced with regular
monitoring of soil pH.
e: CEC should be increased by increasing soil organic matter content (retaining
crop residues, adding organic residues, growing cover crops or companion green
manure crops) in association with a liming program to increase soil pH and therefore
the variable charge component of CEC (e.g., Aitken et al., 1998; Phan & Merckx,
2005). The practicality of adding high activity clays to increase permanent charge
could be assessed (e.g., Noble et al., 2004).
i: The high P-fixation capacity indicates that high rates of P fertiliser will be
required or special P management practices (i.e. sources and method of P fertiliser

5
application) will need to be implemented. P fertilization in minimum input cropping
systems should be directed toward the use of minimal P rates applied in bands or
pockets close to the seed, and the use of crops with low P-demand. Band or spot
placement of water-soluble P fertiliser applications will decrease the loss of P
availability by fixation. However, such placement will concentrate roots around the
fertiliser and this may reduce root exploration of the soil profile. In areas that have
short term droughts, this may limit yield because of restricted root access to soil
water. An initial, reduced rate, broadcast fertiliser application accompanying a banded
application should allow a more uniform root distribution. Soil P test levels should be
determined periodically to monitor soil P status.
geric: These soils have little net variable surface charge and therefore they have a
very limited capacity to retain nutrient cations (eg. calcium and potassium) or anions
(eg. nitrate) in the surface soil. Fertiliser will need to be applied in small frequent
applications in accord with crop nutrient demands. Liming the surface soil to pH (in
water) 5.5 will increase the ability of the soil to retain cations by increasing net
negative variable charge, and this is an important management option. Addition of

6
4. Major Upland Crops grown by Smallholders
Agricultural census data were used to identify the major upland crops grown
by smallholders in Gia Lai. Crop areas are presented in Table 4. Crops occupying
greater than 5% of the arable land are: rice, maize, cassava, sugarcane, rubber and
coffee. Rubber is not grown by smallholders.

Table 4. Crop areas of Gia Lai Province. Smallholder crops are shaded. Crop
Area
(ha)
Proportion
(%)
Rice 63883 20.4
Maize
40486
12.9
Cassava
24297
7.8
Vegetables
7618
2.4
Peanut
3787

identified several soil constraints to crop productivity. Several of these constraints
have effects on crop productivity, irrespective of the crop grown: erosion (er), low
CEC (e), high P fixation (i), low organic carbon (om), K deficiency (k), variable
charge characteristics (geric), hardsetting characteristics (hs) and compaction layers
(comp). However, crops vary in their tolerance to other constraints such as drainage
and acidity; while a particular soil attribute or constraint might be a major limitation
to the productivity of one crop, it may pose only a minor limitation to another. The
FAO (1976) framework for land evaluation uses five classes to categorise the
suitability of a specific soil/landscape unit for growing a particular crop (Table 5). To
facilitate the use of SCAMP for this application, individual soil attributes/constraints
identified for the Ferralsols and Acrisols have been rated according to their effects on
the sustainable production of the major upland crops grown by smallholders in Gia
Lai (Table 6). Ratings are based on collation of information in Williams (1975),
Landon (1984), Page (1984), Schaffer and Andersen (1994), Robinson (1996) and
Dierolf et al. (2001). 7
Table 5. Soil suitability classes [Source: FAO 1976]

Suitability
Class
Criterion Description
1 Highly suitable Soil is suitable for sustainable
production of the crop without
ameliorative measures.
2 Moderately suitable Soil is suitable for sustainable
production of the crop if minor
ameliorative measures are applied (e.g.
liming, mounding to improve local

rating
2 (g
-
) 1 4 3 3 4

3 3 3 3 2 3

4 4 1 2 1 2

5 4 1 1 1 1

6 4 1 1 1 1
Slope (%)
0-2 1 1 1 1 1

2-5 2 1 1 1 1

5-10 3 2 2 2 2

>10 4 3 3 2 3
Soil pH
a
-
1 2 1 1 2

a

2 3 2 2 3
Salinity
s
8
The following comments apply to the management practices that may need to
be undertaken to meet the requirements of individual crops in addition to those
already outlined in Section 3 above.

Texture
S: Because of the low inherent plant available water content of sandy soils,
irrigation may be required for crops of low drought tolerance such as maize,
sugarcane and coffee. Using surface mulches of plant residues will reduce evaporation
and conserve soil moisture.
For crops with high nutrient demands such as maize, sugarcane and coffee, the
low ECEC of sandy soils requires that nutrient cations such as potassium are applied
in split applications at rates in accord with crop demand. Growing green manure crops
or applying plant material from these crops (eg. Tithonia) will temporarily increase
the nutrient holding capacity (i.e. CEC) of the soil.
C: Root crops such as cassava are not suited to clayey soils because of
harvesting difficulties.
Clayey soils are unsuitable for crops that do not tolerate prolonged soil
wetness such as coffee; the low permeability of clayey soils causes them to remain
wet for a longer period than soils of lighter texture.

Drainage
Soils with imperfect or poor drainage are unsuitable for crops that cannot
tolerate waterlogged conditions such as coffee and maize, and raised beds and large
scale drainage works must be undertaken if such crops are to be grown.

Acidity
a: Soils with this constraint are unsuitable for crops with a low or moderate

minimise the effects of these constraints on crop productivity will also vary. However
the use of a liming program and application of green manures to the Ferralsols is
required by all crops, while improving drainage, maintaining a surface mulch, and
applying green manures are essential practices for the Acrisols.

References
Aitken, R.L., Moody, P.W. & Dickson, T. 1998. Field amelioration of acidic soils in
south-east Queensland. I. Effect of amendments on soil properties. Australian
Journal of Agricultural Research, 49, 627-637.
Berding, F.R., Tran Mau Tan, Truong Dinh Tuyen, Tran Van Hue, Deckers, J. &
Langhor, R. 1999. Soil Resources of Gia Lai Province. National Institute of
Agricultural Planning and Projection (Vietnam) and Katholieke Universiteit
Leuven (Belgium).
Dierolf, T., Fairhurst, T. and Mutert, E. 2001. Soil Fertility Kit. Potash and Phosphate
Institute: Singapore.
FAO. 1976. Framework for land evaluation. Soils Bulletin No. 32. FAO:Rome.
Landon, J.R. (ed.) 1984. Booker Tropical Soil Manual. Longman Inc.: New York
Le Trung Lap 2000. Land use and sustainable development for soil resources of Gia
Lai Province. Proceedings of Workshop on Environment and Sustainable
Development of the Central Highland. Pleiku, Sept 2000. Department of
Science, Technology and Environment, Pleiku.
Moody, P.W. and Cong, P.T. 2008. Soil Constraints and Management Package
SCAMP): guidelines for sustainable management of tropical upland soils.
ACIAR Monograph No. 130, 86pp. Australian Centre for International
Agricultural Research, Canberra.
Moody, P.W., Phan Thi Cong, Legrand, J.

& Nguyen Quang Chon 2008.

A framework for identifying soil constraints to the agricultural productivity of

The 85 participants at the training course were given a pre- and post-course questionnaire. The pre-course
questionnaire was designed to determine what the participants considered were the major soil constraints
to productivity in their district. The post-course questionnaire was designed to measure any changed
perceptions of major soil constraints and to determine what follow-up actions the participants planned to
take when they returned from the course.

Pre-course survey
The two major cropping soil groups of the Central Highlands are Ferralsols and Acrisols. These soils are
contrasting in terms of position in the landscape, drainage, texture and clay mineralogy and it was
expected that a wide range of perceived soil constraints would be nominated by the participants,
depending on the soil type in their local area. Table 1 indicates that soil acidity, organic matter content,
slope and erosion and nutrient deficiencies were perceived to be the major constraints. Other important
constraints such as soil compaction, clay dispersion and shallow rooting depth were not perceived to be
important constraints.

Table 1. Soil properties/constraints which are perceived to be related to the decline in soil productivity
in Gia Lai Province.

Soil properties Pre-course Post-course
(%) (%)
1 pH 35.7 33.3
2 Texture 16.7 31.0
3 Organic matter content, humus 21.4 31.0
4 Drainage 19.0 9.5
5 Structure, aggregation 14.3 16.7
6 Erosion, slope 21.4 42.9
7 Rooting depth 11.9 4.8
8 Compaction 4.8 9.5
9 Porosity, aeration 9.5 11.9
10 Color 7.1 4.8

Issue (%)
Balanced nutrient/fertilization 47.6
How to make fertilizer recommendation for major crops 90.5
More field practice on more soil types 66.7
More training courses for other farmers 19.0
Produce seeds of green manures 35.7
SCAMP Level 3 training 81.0
Mobile lab application 69.0 Future action plans
The future action plans of the participants primarily involve the dissemination of SCAMP training to other
extensionists, farmer associations and farmers at village level (Table 3), with a major emphasis on soil-
specific management and erosion control. The use of leguminous green manure crops to control erosion
and to provide nitrogen to replace chemical fertilizers (thus reducing investment costs) was one
management strategy that many course participants intend to promote. There is also the intention to map
soil constraints at local level.
009/06 VIE Six-monthly Report_April 2008

3Table 3. What actions are the participants planning to undertake with their local farmer networks after
coming back from the workshop.

(%)
Organize SCAMP training course for the village leaders (down to
hamlet level)
28.6
Apply erosion control with leguminous/vetiver contour
009/06 VIE Six-monthly Report- April 2008

1
Attachment 3

009/06 VIE: Improving capability of provincial extensionists for assessing
soil constraints to sustainable production through the use of the SCAMP
decision support system.
Summary of Demonstration Field Experiment- Central
Highlands Introduction
Sustainable agricultural systems are based on managing soils according to their
capabilities and environmental constraints. The productive capacity of a soil is
determined by key soil properties: some are intrinsic (such as texture and structure) while
others (such as pH and organic matter content) can be manipulated by management.
Knowledge of the intrinsic properties of a soil enables inferences to be made about
derived properties such as CEC and pH buffer capacity. From these inferences,
management strategies can be developed for maximising the productive capacity of the
soil.

To facilitate the interpretation of upland soil properties for identifying soil constraints and
appropriate management strategies, a decision support framework ‘Soil Constraints and
Management Package’ (‘SCAMP’) was developed in ACIAR project SMCN 2002/085.

fertiliser applications will decrease the loss of P availability by fixation. However, such
placement will concentrate roots around the fertiliser and this may reduce root exploration
of the soil profile. In areas that have short term droughts, this may limit yield because of
restricted root access to soil water. An initial, reduced rate, broadcast fertiliser application
accompanying a banded application should allow a more uniform root distribution. Soil P
test levels should be determined periodically to monitor soil P status.
geric: These soils have little net variable surface charge and therefore they have a
very limited capacity to retain nutrient cations (eg. calcium and potassium) or anions (eg.
nitrate). Fertiliser will need to be applied in small frequent applications in accord with
crop nutrient demands. Liming the surface soil to pH (in water) 5.5 will increase the
ability of the soil to retain cations by increasing net negative variable charge, and this is
an important management option. Addition of organic materials such as green manure
crops should be considered because this may also increase net negative variable charge.

To validate the applicability of the formulated management strategies, a field site on a
Ferralsol was selected in Ia Grai District (N13
o
58.01
'
, E107
o
52.98
'
). Some properties of
the soil are presented in Table 1.

Table 1. Some properties of the field site soil (0-15 cm).

Soil pH
(

season) comprised the demonstration trial used to support the SCAMP training workshop
held in Gia Lai as a component of this project.

009/06 VIE Six-monthly Report- April 2008

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Individual plot size comprised 5m of 4 double rows of maize at 1.5 m spacings. There
were 4 replicates arranged in a randomised block design. Erosion control measures were
implemented by planting contour rows of green manure crops and vetiver grass.
009/06 VIE Six-monthly Report- April 2008

4
Table 2. Treatments at the Ia Kha field experiment on a Ferralsol. Maize was the
test crop. Benefit/Cost ratios were calculated as Gross Return/Gross Inputs. Gross return
comprises sale of grain. Gross inputs comprise fertiliser costs, and labour costs associated
with collecting the locally available green manure Tithonia. For calculating the cost of
bentonite additions, 1/5 of the initial cost of each of the additions was used each year
(assumes a 5 year residual value) and for the silicate, 1/3 of the initial cost of the addition
was used each year (assumes a 3 year residual value).

2005 cropping season

Treatment Grain Yield
(T/ha)
Benefit/Cost
1. Farmer's practice (71N, 21P, 20K, 39S) 0.2 d -0.4
2. High P recommendation (115N, 57P, 140K) 1.8 bc 1.3
3. Bentonite @ 5T/ha (115N, 42P, 140K) 2.3 ab 1.4
4. Tithonia @ 10 kgP/ha incorporated (115N, 42P, 140K) 2.3 ab 2.7
5. Tithonia + bentonite (115N, 42P, 140K) 2.8 a 2.3

4. Residual Tithonia (115N, 29P, 50K)
3.4 3.9
5. Residual Tithonia + bentonite (115N, 29P, 50K)
3.4 2.1
6. Dispersed P (115N, 29P, 50K)
3.1 3.6
7. Calcium silicate (115N, 29P, 50K)
2.9 1.9
For Treatments 2-7, fertiliser applications were split: 30%N, 40%K, 100%P at planting
30%N, 20%K 30 DAS
40%N, 40%K 60 DAS
009/06 VIE Six-monthly Report- April 2008

5

Results
Results from the final year of the experiment indicated that yield increased in the order:
farmer practice<calcium silicate=high P recommendation=dispersed P<residual bentonite
= residual Tithonia = residual Tithonia plus bentonite. The reason for the poor yield in the
Farmer's Practice relative to the same total nutrient inputs in other treatments was caused
by the farmer splitting the application of the blended N-P-K fertiliser. While this practice
is efficient for the application of N and K, splitting the application of P did not provide
sufficient P at planting to meet crop requirements. Plant weight and plant chemical
analyses determined at 35 days after sowing indicated low yield and P content in
Treatment 1 relative to the other treatments. This result highlights the benefits of using
'straight' fertiliser forms rather than blends or compound fertilisers.
In the first two seasons, soil and plant analyses indicated that as well as providing 'slow
release' N and P, Tithonia increased soil pH (thus ameliorating Al toxicity) and increased
ECEC. Bentonite application also increased ECEC, preventing the leaching of added K
into the subsoil. These results confirm the constraints identified in the SCAMP analysis of