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Major Cropping Soils and Soil Constraints to Productivity of Major Upland Crops Grown by Smallholders 3.. Therefore, once the constraints of a particular soil type have been identified

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 MoodyA and Phan Thi CongB

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

Australia

BInstitute 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:

• review existing information on the identification and extent of upland

cropping soils in focus provinces of Vietnam

• identify the major soils used for smallholder cropping in the focus provinces, and determine their constraints by the application of SCAMP

• identify the major crops/cropping systems used by smallholders in the focus provinces, and document the specific soil requirements of these

crops/cropping systems

• 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

Part 3 focuses on the soils and cropping systems of the South East Region

comprising five provinces (Binh Phuoc, Binh Duong, Tay Ninh, Dong Nai, Ba Ria Vung Tau) and the suburbs of Hochiminh City The region stretches from 105o 49’ to

107o 35’ east longitude and from 10o 20’ to 12o 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/cm2/year which is favourable for agriculture production Annual mean

temperature is 26-27oC 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

Ancient alluvia cover about 33% of the South East Region The depth of this material varies from 2-7 m and is predominantly grey in colour Particle size of the alluvia ranges from coarse sand to clay Depending on formation processes, ancient alluvial has weathered into two different soil groups: grey degraded soils and

yellowish brown soils

Other major parent materials are granite (Nui Ba, Tay Ninh Province; Ba Ra, Binh Phuoc Province) and schist in the mountainous areas of Tan Uyen, Dong Phu, and Phuoc Long Districts, Binh Phuoc Province

3 Major Soil used for Smallholder Cropping

The South East Region has nine major soil groups (Table 1), with Ferralsols and Acrisols comprising the two major soil groups and accounting for 75% of the

total area

Table 1 Major soil groups in the South East Region of Vietnam (Source: Phạm Quang Khánh, 1997)

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 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 than on the top of plateaus as occurs in the Central Highlands

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 and

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

Acrisols

Large areas of Acrisols are used for growing sugarcane, with Tay Ninh

Province having the largest area Soil properties of some sugarcane fields are

presented in Table 2

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

Ca2+

(cmolc kg -1 )

Exch

Mg2+

(cmolc kg -1 )

CEC

(cmol c kg -1 )

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 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

5 Major Upland Crops grown by Smallholders

Maize, sugarcane and peanut are the major smallholder crops and the

production areas are indicated in Table 3

Table 3 Total areas (x 1000 ha) of maize, sugarcane and peanut grown in the South East Region of Vietnam in 2006 and 2007 (Source: Statistical Year Book 2007)

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

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 income/investment cost ratio of sugarcane is presented in Table 4 Results show that mulching improves yield and income compared with residue burning

Table 4 Effect of different mulching techniques on the income/cost ratio

(Source: Do Ngoc Diep, 2005)

Yield at 10 CCS (tonnes/ha)

Product value (1.000đ)

Investment cost (1.000đ)

Income (1.000đ/ha)

Income/cost ratio

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)

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 Maize Sugarcane

Peanut

Main nutrient

/water uptake zone

(cm)

100

Nutrient

needs

High N, K req'd

High N req'd Ca in pegging

zone

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

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 the South East Region The constraints to crop production which are likely to occur in the Ferralsols are acidity, low nutrient cation retention, and high P fixation 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

The upland crops most commonly grown by smallholders in the region are maize, sugarcane and peanut 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

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