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Major Cropping Soils and Soil Constraints to Productivity of Major Upland Crops Grown by Smallholders I.. Crops vary in their tolerance to soil constraints and a soil property limiting

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 MoodyA and Phan Thi CongB

A

Queensland Department of Natural Resources and Water, Indooroopilly, Qld 4068,

Australia

B

Institute of Agricultural Sciences of Southern Vietnam, Ho Chi Minh City,

Vietnam

1 Introduction

The Soil Constraints and Management Package (SCAMP) has been developed

to identify soil constraints to crop production by considering a range of key soil

properties (Moody and Phan Thi Cong 2008; Moody et al 2008) Once these

constraints have been identified, management practices that ameliorate or modify

these constraints can be formulated Crops vary in their tolerance to soil constraints

and a soil property limiting the productivity of one crop may not be a limitation to the

productivity of another crop Therefore, once the constraints of a particular soil type

have been identified, the soil can then be assessed for its ability to potentially support

the production of specific crops

The objectives of this series of reports are to:

ƒ review existing information on the identification and extent of upland

cropping soils in focus provinces of Vietnam

ƒ identify the major soils used for smallholder cropping in the focus

provinces, and determine their constraints by the application of SCAMP

ƒ identify the major crops/cropping systems used by smallholders in the

focus provinces, and document the specific soil requirements of these crops/cropping systems

ƒ link soil constraints to the soil requirements of the major upland crops

and develop management guidelines for the management of specific soil types for specific crops

Report I focuses on the soils and cropping systems of Gia Lai Province

2 Major Soils used for Smallholder Cropping

The areal extents of the different soil groups (FAO-UNESCO classification)

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

Chromic and Haplic Acrisols

Acric,Humic and Vetic Ferralsols

756,433 49 Dystric and Gleyic Arenosols

Luvisols

364,638 23

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

TOTAL 1,549,571

The land forms of Gia Lai have been classified (Berding et al., 1999) as:

ƒ Hills and low mountains,

ƒ Basaltic plateaus,

ƒ Gently to rolling uplands on metamorphic or granitic rocks or on recent alluvium and

ƒ Depositional areas

Topography (slope) limits the agricultural use of many areas of Gia Lai, and the major soil groups of agricultural importance are the Ferralsols and Acrisols occurring on the basaltic plateaus and gently to rolling uplands These soil groups comprise about 49%

of the land surface of the province (Table 1, line 1)

3 Soil Constraints and Management Practices for Sustainable Crop Production

In a recent study (Moody et al 2008), sites identified on the 1:100,000 soils

map of Gia Lai Province as 'Red-brown soils on basalt' (Ferralsols) and 'Grey soils on acid igneous rocks' (Acrisols) (Le Trung Lap, 2000) were selected from the basaltic plateaus and gently to rolling uplands areas Fourteen Ferralsols were sampled under a range of land uses (maize-upland rice, maize-cassava, rubber, coffee, eucalypt

plantation, fruit trees, cashew) in Dak Doa, Mang Yang, Chu Pah, Ia Grai, Duc Co, Chu Prong and Chu Se Districts of north west Gia Lai Province Sixteen Acrisols were sampled from various positions (upper, mid, lower slope) in the landscape under several land uses (maize, cassava, sugarcane, vegetables) in the vicinity of Dak Po Village, Dak Po District in the east of Gia Lai Province

Mini-pits were dug at each site and SCAMP Level 1 and Level 2 assessments made (Table 2) A composite 0-15 cm soil sample was taken from each site to

represent the plough layer and analysed for Level 3 attributes (Table 2)

Table 2 Attributes determined for each application level of SCAMP

Level 1 Texture, colour (moist) of soil matrix and mottles, structure and consistence (moist),

drainage class, permeability class, slope, erosion hazard, gravel content, compaction Level 2 Field pH (water and 1M KCl), field EC, dispersion class, infiltration rate

Level 3 Organic C, clay %, P fixation capacity, exchangeable Ca, Mg, Na and K, extractable

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)

Table 3 SCAMP descriptors for 14 Ferralsols and 16 Acrisols of Gia Lai

Province, Vietnam Number of sites with the attribute is in parentheses

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)

Variable charge characteristics geric (4)

Hard-setting hs (2)

Compaction comp (4)

These assessments indicate that the Ferralsols are predominantly loamy in

texture, with a range of erosion hazards depending on site slope The main pathways

of water movement are by drainage or runoff plus drainage They typically have a low

soil pH (<5.2 in water) but a low acidification hazard because of their high organic C

and clay content ECEC is typically very low (<4 cmolc/kg) and they have a high P

fixation capacity The variable charge component of several of the soils is near, or at,

the point of zero net charge (pHKCl-pHwater ranging between -0.10 and 0.10)

The Acrisols are predominantly loamy in texture, although a loamy surface

over a sandy subsurface sometimes occurs Erosion hazard ranges from slight to

extreme depending on site slope Drainage is the main pathway of water movement in

half of the sites, with the remainder exhibiting runoff plus drainage or runoff

pathways Acidity constraints are not common, but most of the soils have a moderate

acidification hazard because of their low clay and organic matter contents Low

subsurface K reserves commonly occur Hard-setting surfaces or compaction

occurred at several sites

The main constraints identified for the Ferralsols were acidity (a), low nutrient

retention (e), high P fixation (i), and variable charge characteristics (geric), with

drainage being the most common pathway of water movement (Table 2) With these

constraints, the SCAMP database would indicate the following management strategies

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

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 organic materials such as green manure crops should be considered because this may

also increase net negative variable charge

With respect to the Acrisols, the most commonly identified constraints were low-moderate organic matter ratings, low K reserves particularly in subsurface layers, and the soil physical problems of hard-setting surfaces and compaction Some individual sites suffered from impeded drainage leading to waterlogging and ponding of water

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 forage grasses, retaining all crop residues in the field where the crop has grown, not burning crop residues, minimum or zero tillage farming systems, strip or alley cropping and application of organic materials (such as animal manure, composted municipal waste,

sewage sludge, and locally available industrial organic wastes) obtained from off-site

k: Potassium fertilisers or organic amendments having a significant content of K

will need to be applied In soils with low K reserves in the subsurface layer, it is likely that crops will exhibit K deficiency during periods of drought In these circumstances, placement of K fertilisers below the seed at sowing or mixing K fertiliser through the soil in the planting hole is a more efficient management strategy than sidedressing K fertilisers on the soil surface Crops should be closely monitored for K deficiency symptoms

hs, comp: Hard-setting surfaces reduce infiltration rate and cause poor crop

establishment, while compaction layers restrict root growth and limit rooting depth causing drought stress to crops Retaining crop residues and applying surface mulch should be used to maintain soil surface moisture thus minimising hard-setting To minimise compaction risk, soils should only be cultivated when drier than their plastic limit, and tillage and machinery traffic should be avoided when soil is wetter than its plastic limit

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 (%)

TOTAL 312983

5 Soil Suitability for Major Upland Crops grown by Smallholders

SCAMP assessments of the Ferralsols and Acrisols (Section 3 above) have 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)

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 drainage)

3 Marginally suitable Soil is only suitable for sustainable

production of the crop if major ameliorative measures are undertaken (e.g large scale drainage works)

4 Currently not suitable Soil is not suitable for sustainable

production of the crop

Table 6 Suitability class of soil attributes/constraints for production of specific

crops

SCAMP descriptor

Paddy rice

Maize Cassava Sugarcane Coffee

>10 4 3 3 2 3

Salinity s -

s

2

3

3

4

3

4

2

4

3

4

Main nutrient

/water uptake zone

(cm)

<50 80-100 >100 >100 >100

Nutrient

needs

High N

req'd

High N, K req'd

Tolerates low fertility

High N req'd High N, K

req'd

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

tolerance to Al and/or Mn toxicity such as maize and coffee unless a comprehensive liming program is undertaken

a - : These soils require a liming program if they are being used to grow crops

of low tolerance to Al toxicity such as maize and coffee Applying Tithonia residues

to acidic soils has been shown to ameliorate soil acidity by increasing soil pH An added benefit of using fused magnesium phosphate (FMP) as a P fertiliser is that it also has a liming effect

Main nutrient/water uptake zone

Crops with a comparatively shallow active rooting depth will not be as

sensitive as deeper rooted crops such as coffee and sugarcane to constraints such as a

compaction layer (comp)

Conclusions

Ferralsols and Acrisols are the major arable soil groups in Gia Lai The

constraints to crop production which commonly occur in the Ferralsols are acidity, low nutrient cation retention, high P fixation and variable charge characteristics, with drainage being the most common pathway of water movement For Acrisols,

commonly occurring constraints are low-moderate organic matter ratings, low K reserves particularly in subsurface layers, and the soil physical problems of hard-setting surfaces and compaction Some Acrisols have impeded drainage leading to waterlogging and ponding of water

The crops most commonly grown by smallholders in the province are: paddy rice, maize, cassava, sugarcane and coffee Individual crop tolerances to some of the identified constraints vary, and so soil management responses to ameliorate or

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

tropical upland soils Soil Use and Management, 24, 148-155

Noble, A.D., Ruaysoongnern, S., Penning de Vries, F.W.T., Hartmann, C & Webb,

M.J 2004 Enhancing the agronomic productivity of degraded soils in

northeast Thailand through clay-based Interventions In: Water and

Agriculture (eds Seng, V., Craswell, E., Fukai, S & Fischer, K.), ACIAR

Proceedings No 116, ACIAR, Canberra, pp 147-160

Page, P.E 1984 Tropical Tree Fruits for Australia QDPI Information Series QI

83018 Queensland Department of Primary Industries: Brisbane

Phan & Merckx Phan, T.C & 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 & Andersen, P.C 1994 Handbook of Environmental Physiology of Fruit Crops CRC Press: Florida

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

Press: London

009/06 VIE Six-monthly Report_April 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

SCAMP Training Course Gia Lai: March 2008

Pre- and Post- training survey

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