009/06 VIE Six-monthly Report- October 2008
Attachment 2 009/06 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

3. South East Region
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,

o
35’ east longitude and from 10
o
20’ to 12
o
17’ north attitude. The total area is
about 2.2 million hectares (approximately 20.3% of the total land area of Vietnam).
The South East Region receives the highest solar radiation in Vietnam- more than 130
Kcal/cm
2
/year which is favourable for agriculture production. Annual mean
temperature is 26-27
o
C and constant throughout the year. The region receives a high
annual rainfall, from 1800-2400 mm. Rainfall is concentrated in the rainy season
(May to November, 200-300 mm per month) causing soil erosion in sloping areas and
severe leaching of the soil profile. Mean annual evaporation is about 1200-1400 mm.
Because of its favourable climate, the South East Region produces many high value
crops such as rubber, coffee, black pepper, sugarcane, maize, fruit trees and
vegetables. 2. Parent Materials
Basaltic materials of the Pleistocene and Pleistocene-Holocene periods cover
more than 25% of the region (Phan Lieu, 1992). Through a long weathering process,
soils with ‘laterite’-bauxite layers containing nodules are found in the north of Binh
Duong province (Phuoc Long and Dong Phu Districts). The younger basalts form
brownish red soils with a soil depth of 8-10 m in average. These soils are found in
Loc Ninh, Binh Long, Phu Rieng, Xuan Loc, and Dat Do Districts and near the border
with Cambodia in Tay Ninh Province.

8 Skeletal soils (Leptosols) 13.195 <1
9 Saline soils (Fluvisols) 2.500 <1 Ferralsols have good soil physical properties but are poor in chemical fertility.
These soils are important for growing perennial crops such as black pepper, rubber,
fruit trees, cashew and coffee.
Small areas of Acrisols are located at low altitudes and are therefore mostly
used for rice production. Larger areas at high elevation are used for perennial crops
(rubber, coffee, cashew, sugarcane) and annual crops such as cassava, peanut, maize
and vegetables.
Acid sulphate soils occur in low landscape positions near Hochiminh City.
Eucalyptus, pineapple, sugarcane and rice are grown on these soils.
Black soils are found in Dong Nai Province on basaltic materials and in foot-
slope positions in Tay Ninh Province.

4

4. Soil Constraints and Management Practices for Sustainable Crop Production
In general most of the soils in the South East Region are acidic, with low
organic carbon contents and low CEC. Soil constraints to crop production will be
discussed for the two major soil groups: Ferralsols and Acrisols.
Ferralsols
The main constraints identified for the Ferralsols in the region are acidity (a),
low nutrient retention (e) and high P fixation (i). Unlike Ferralsols of the Central
Highlands, variable charge characteristics (geric) are not common in this region. This
could be due to the basalt materials in the South East Region being younger in age,
and therefore less weathered than the basalts of the Central Highlands. Drainage is
the most common pathway of water movement but surface runoff is also a severe
problem as most of the Ferralsols occur in sloping positions in the landscape rather

5
Table 2. Soil properties of some soils growing sugarcane in Tay Ninh Province.
(Source: Sugarcane Research and Development Centre, the IAS)

No.
pH
KCl
Organic
C
(%)

Total
N
(%)
Olsen
P
(mg/100g)
Exch
K
+

(cmol
c
kg
-1
)

Exch
Ca
2+

10 4.13 1.38 0.081 0.4 0.06 1.1 0.7 3.8
11 4.12 1.32 0.083 0.4 0.09 1.0 0.6 3.6
12 4.01 1.38 0.072 1.2 0.04 0.8 1.0 2.6
13 3.85 1.33 0.045 0.1 0.03 0.7 0.5 3.7
14 4.16 1.28 0.067 0.6 0.10 0.6 1.2 3.7
15 4.06 1.28 0.063 0.8 0.04 0.6 0.2 3.0
16 4.00 2.76 0.116 0.8 0.03 0.5 0.3 5.5
17 4.07 2.86 0.073 0.7 0.03 0.6 0.3 6.0

Information from Table 2 indicates that the soils are acidic. Soil organic matter
is generally higher compared with other Acrisols probably due to the recycling of root
residues from ratoon sugarcane crops and the common practice of minimum tillage
(Phan Thi Cong, 1997). The soils have a low CEC and low base saturation.
Additional information on the constraints of Acrisols was obtained by the
project 'Sustainable Agricultural Development in the Uplands of South Vietnam'
(IAS- KUL, 1998). The most commonly identified constraints were low-moderate
organic matter ratings, low K reserves particularly in subsurface layers, and soil
physical problems of hard-setting surfaces and compaction. Some individual sites
suffered from impeded drainage leading to waterlogging and ponding of water. Iron
leaching leaves a typical grey color in the profiles of many Acrisols in the region. In
addition, plinthite in the sub horizons threatens the sustainability of these soils due to
the upwards movement of Fe oxides/hydroxides as a result of capillary rise associated
with high evaporation. Soil compaction very near to the soil surface is a common
constraint.
To address these constraints, the SCAMP database would indicate the
following management strategies:
om (low-moderate): Increasing the levels of organic matter in these soils
would improve nutrient supply, increase CEC, increase water holding capacity and
increase pH buffer capacity. The management of soil organic matter in tropical soils
involves mulching and incorporation of ‘green manure’ crops such as legumes or

Year 2006 2007 2006 2007 2006 2007
Ba Ria Vung Tau 19,0 18,8 0,4 0,5 1,4 1,7
Binh Duong 0,8 0,6 1,1 1,1 3,6 3,0
Binh Phuoc 7,0 6,3 0,8 0,7 1,7 1,2
Dong Nai 56,7 58,2 8,8 8,9 1,6 1,4
Tay Ninh 7,8 7,1 38,0 31,3 20,9 21,3
Hochiminh City 1,2 1,1 2,3 2,0 0,7 1,0

Maize is grown mainly in Dong Nai Province on fertile Luvisols or Lixisols.
On these soils, maize can give high yields of up to 10 tonnes/ha. In Ba Ria Vung Tau
and Tay Ninh Provinces, maize is grown on Acrisols and Ferralsols. Sugarcane is
mainly grown in Tay Ninh Province, and to a lesser extent, Dong Nai Province. A
few years ago, large areas of sugarcane could be found in Binh Duong Province on
Acrisols, but this crop has given way to the urbanization of the province. Peanut has
been grown on the grey degraded soils of Tay Ninh Province for more than 40 years
and still comprises a major crop of the province.
Water availability is the main factor controlling the cropping patterns of the
region. After a long dry season, annual crops such as rice and maize are grown when
the rain starts. Paddy rice is the main crop grown in the low position lands while
maize is grown on the higher land. Peanut or mungbean are planted at the end of the
wet season which coincides with the winter-spring season. Perennials of importance
such as black pepper or coffee are grown in low positions of the landscape where
irrigation water can be managed in the dry season. Imbalanced fertilization is a

7
constraint in management practices of farmers in the region. The efficiency of
nutrient use is very low.
In the South East Region, 83% farmers burn sugarcane crop residues (leaves
and cane top) (Nguyễn Thị Rạng, 2002). The effect of different mulching techniques
using the crop residue of the first crop to cover the ground of the ratoon crop on the


6. Soil Suitability for Major Upland Crops grown by Smallholders
SCAMP assessments of the Ferralsols and Acrisols (Section 4 above) have
identified several soil constraints to crop productivity. Some 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), and hardsetting
characteristics (hs). 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 Acrisols and Ferralsols have been rated
according to their effects on the sustainable production of the major crops grown by
smallholders in the South East Region (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). 8
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


O 3 3
3
Drainage
1 (g) 4 4
4
rating
2 (g
-
) 4 3
3

3 3 2
3

4 1 1
2

5 1 1
1

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

2-5 1 1
1


zone
9
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 4 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

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. and 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.

Dierolf, T., Fairhurst, T. and Mutert, E. 2001. Soil Fertility Kit. Potash and Phosphate
Institute: Singapore.

Do Ngoc Diep 2005. Nghiên cứu một số biện pháp kỹ thuật chăm sóc mía ban đầu
cho cây mía ở Nam Bộ. Project Report. Centre for Sugarcane Research and
Development. Institute of Agricultural Sciences of Southern Vietnam.

FAO. 1976. Framework for land evaluation. Soils Bulletin No. 32. FAO: Rome.

Institute of Agricultural Sciences of Southern Vietnam and Katholieke Universiteit
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Moody, P.W. and Cong, P.T. 2008. Soil Constraints and Management Package
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ACIAR Monograph No. 130, 86pp. Australian Centre for International
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Moody, P.W., Phan Thi Cong, Legrand, J.



Phan, T.C. and Merckx, R. 2005. Improving phosphorus availability in two upland
soils of Vietnam using Tithonia diversifolia H. Plant and Soil 269, 11-23.

Robinson, J.C. 1996. Bananas and Plantains. CAB International: Oxon.

Schaffer, B. and Andersen, P.C. 1994. Handbook of Environmental Physiology of
Fruit Crops. CRC Press: Florida.

Statistical Year Book, 2007. Statistical Publishing House: Hanoi.

Williams, C.N. 1975. The Agronomy of the Major Tropical Crops. Oxford University
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