Major Cropping Soils and Soil Constraints to Productivity of Major Upland Crops Grown by Smallholders 2.. Major Soils used for Smallholder Cropping Acrisols, Fluvisols and Arenosols co
Trang 1009/06 VIE Six-monthly Report- October 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
2 Southern Central Coast
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
Trang 21 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 2 focuses on the soils and cropping systems of the Southern Central Coast comprising Quang Nam, Quang Ngai, Binh Dinh, Phu Yen, Khanh Hoa, Ninh Thuan, and Binh Thuan Provinces
2 Climate and Landforms
The region has a typical tropical monsoon climate with an annual temperature of around 24oC-27oC on average (minimum 20oC-21oC and maximum 31oC-32oC) Total heat accumulation per annum is 8,000oC– 9,500oC, with annual solar radiation of 140 Kcal/cm2 Annual rainfall ranges from 500 mm to 2,500 mm with an average
humidity of 70-80% Differences in regional rainfall have resulted in the identification
of 3 major agri-ecological zones:
• Nam-Ngai (Quang Nam & Quang Ngai): 2000-2600 mm ;
• Binh–Phu (Binh Dinh & Phu Yen): 1500-1700 mm; and
• Southern Ca Pass (Khanh Hoa, Ninh Thuan): < 600 mm
The landforms of the Southern Central Coast comprise:
(i) mountains and midlands, (ii) river deltas, and
(iii) coastal sand dunes, floodplains and swamps
Trang 33 Major Soils used for Smallholder Cropping
Acrisols, Fluvisols and Arenosols comprise the major soil types of the South
Central Coast of Vietnam The areal extents of the soils are given in Table 1 Of the
total land area of the Southern Central Coast, about 19% comprises land that is
suitable for agriculture (of which about 21% is cultivated), 39% comprises forestry
land, and 35% comprises unused land, rivers and streams
Table 1 Areas of major soil groups in the South Central Coast of Vietnam
Soil type Area Proportion
Ferralitic grey soils (Ferric Acrisols) 299,512 54.9
Acidic alluvial soils (Dystric Fluvisols) 59,466 10.9
Grey soils with yellowish red mottles (Plinthic Acrisols) 53,465 9.8
Source: Nguyen thi Ngoc Hue et al (2008)
4 Soil Constraints and Management Practices for Sustainable Crop Production
The following general constraints to agricultural productivity have been identified
for the Southern Central Coast:
• the soils are generally low in nutrients and are acidic (low water and nutrient retention capacity);
• drought is common due to irregular rainfall and high evaporation during the dry season;
• wind and water erosion is common as a result of the sloping topography with limited groundcover;
• soil degradation and desertification are common particularly in Quang Ngai and Binh Dinh Provinces;
• flooding often occurs in the wet season;
• sand encroachment occurs inland due to strong winds and limited groundcover
It is evident from Table 1 that Acrisols, Fluvisols and Arenosols occupy the
greatest proportion of the land surface of the South Central Coast Constraints and
management strategies for Acrisols in the Central Highlands have already been
discussed in Part 1 of this series of reports (Moody and Cong 2008), and these
constraints and strategies would be equally applicable to the Acrisols of the South
Central Coast Consequently, this report will consider the constraints and management
Trang 4In a limited assessment of the soils of Binh Thuan Province, Moody et al
(2005) identified several constraints of the sandy soils (Arenosols) and the alluvial
soils (Fluvisols) (Table 2)
Table 2 SCAMP descriptors for 4 Arenosols and 5 Fluvisols of Binh Thuan
Province, Vietnam The number of sites with the attribute is in parentheses
runoff/ponding (4)
These assessments indicate that the Arenosols are sandy in texture, with low
organic matter content, low CEC, and high to very high acidification hazard
Potassium status is low Drainage is the main pathway of water movement
Compaction is a constraint in those Arenosols that have a predominantly fine sand
component (20-200 µm)
The Fluvisols are predominantly clayey in texture Depending on site slope,
runoff or ponding is the main pathway of water movement Acidity constraints are not
common Low soil K reserves and hard-setting surfaces are common
With these constraints, the SCAMP database would indicate the following
management strategies for sustainable productivity:
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)
om (low): 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
Trang 5hs, 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
Agricultural census data (1999) were used to identify the major crops grown
by smallholders in the Southern Central Coast Where available, crop areas are
presented in Table 3 Smallholder crops with significant areas are rice, maize,
cassava, sugarcane, and peanut In general, coconut, cashew and rubber are grown in commercial plantations
Trang 6Table 3 Crop areas of the Southern Central Coast All crops except rubber are grown by smallholders
Crop
Area (ha)
Rice 540000 Sugarcane 71067
6 Soil Suitability for Major Upland Crops grown by Smallholders
SCAMP assessments of the Arenosols and Fluvisols (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: low CEC (e); low organic carbon (om); K deficiency (k); 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 4) To facilitate the use of SCAMP for this application, individual soil attributes/constraints identified for the Arenosols and Fluvisols have been rated according to their effects on the sustainable production of the major crops grown by smallholders in the Southern Coastal Region (Table 5) 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)
Trang 7Table 4 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 5 Suitability class of soil attributes/constraints for production of specific
crops
SCAMP descriptor
Paddy rice
Maize Cassava Sugarcane Coffee Peanut
s
2
3
3
4
3
4
2
4
3
4
3
4
Main nutrient
/water uptake zone
(cm)
80-100
>100 >100 >100 50-
100
Nutrient
needs
req'd
High
N, K req'd
Tolerates low fertility
High N req'd
High N,
K 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
Trang 8Texture
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, Acrisols, Arenosols and Fluvisols are the major arable soil groups
in the Southern Central Coast The constraints to crop production which commonly occur in the Arenosols are low plant available water capacity, low nutrient cation retention, K deficiency, acidity, low organic matter, and compaction in soils with high fine sand content Drainage is the dominant pathway of water movement For
Fluvisols, commonly occurring constraints are low K reserves, occasional acidity, and the soil physical problem of hard-setting surfaces Fluvisols have impeded drainage leading to runoff on slopes or ponding in low-lying areas
The crops most commonly grown by smallholders in the region are: paddy rice, maize, cassava, sugarcane, coffee and peanut Individual crop tolerances to some
of the identified constraints vary, and so soil management responses to ameliorate or
Trang 9minimise the effects of these constraints on crop productivity will also vary In
general, however the Arenosols and Fluvisols would benefit from application of K fertilisers and reduced cultivation (to reduce the risk of compaction and hard-setting) Increasing the organic matter content of Arenosols is essential Fluvisols may require raised beds to improve drainage in the root zone of upland crops
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