IJERD – International Journal of Environmental and Rural Development (2011) 2–1

Research article
erd

The Rice Soil Fertility Capability Classification System
VO QUANG MINH
Department of Land Resources, Cantho University, Vietnam
Email: vqminh@ctu.edu.vn
Received 2 December 2010

Accepted 10 February 2011

Abstract The Rice Soil Fertility Capability Classification (RSFCC) is based on FCC(Fertility Capability Classification) system, with some modifications. The system deals
with soil morphology, physics, and chemistry characteristics. Most of the class limits ofmodifiers are borrowed from soil taxonomy, others could be from field observation, which
consists of 4 categories and based on three soil layers. The upper layer coincides with the
top 20cm or Type (C for clay and L for Loamy). The soil below the upper layer from 20 to
50cm is referred to the Substrata Type (C for Clay and L for Loamy), and from 50 to100cm is referred to Subsoil Type (C for Clay, L for Loamy, and S for Sandy). The
condition modifiers, directly relevant to plant growth, include a, a- c, c-, e, f, f-, g+, i, n-, s,s-, o, p. Some modifications and additions for classification are suggested, in which newmodifiers of p (low P available), o (low organic carbon), c, c- (actual acid sulfate), f, f(potential acid sulfate) are added, the former c condition modifier (sulfidic) divided into c(actual acid sulfate) and f (potential acid sulfate). Modifiers of a, i, n, s, are suggested withmodifications from FCC system. The classes within each category and assigned modifiersfor each soil type/substrata type/subsoil type are different, which is followed by modifiers
presented.
Keywords FCC, fertility capability classification, modifier, rice

INTRODUCTION
Soil is a component of the natural medium that acquires its morphology and properties after a longand slow evolution after reaching equilibrium with environmental conditions. The data from fieldtests or from yield production provided by individual farmers records or else are usually local,
spotty, and sometimes not reliable and are generally difficult to extrapolate. Therefore, theevaluation is normally conducted indirectly on the basis of the soil properties. The evaluations
made should be validated finally with real constraints and yield data. According to Sanchez et al(2003), the problem with soil taxonomy is that it quantifies only permanent soil parameters, mostof which are located in the subsoil. Soil taxonomy ignores many dynamic parameters crucial tocrop productivity, which are mostly in the topsoil where the majority of plant roots are located,both in natural and agricultural systems. To overcome this limitation, a fertility capability soil
classification system (FCC) was developed to interpret soil taxonomy and soil tests in aquantitative manner that is relevant to growing plants (Buol et al., 1975). It is now widely used andis included in the FAO soils database (FAO, 1995).
Based on the developed FCC system by Sanchez et al (2003), the research suggests theframework for developing the system for rice soil fertility classification and recommendation,
where soil environment is effected such as soil acidity, agrochemical uses of fertilizer, pesticide,etc, and soil nutrient degradation. The recommended system is useful for farmers or agriculturalextension workers to classify their soil, due to its simplicity and easy to apply by using simple lab
analytical methods or field identification, with some recommendations for proper soil fertility
improvement.

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THE CONSTRAINS FOR RICE CULTIVATION RELATED TO SOIL MODIFIERS OR
INDICATORS IDENTIFIED
The system was developed based on the soil constraints for rice cultivation, related to suggested
system condition modifiers. The attributes used in the system are the lower-case letters of theconstraints that have been identified for that soil, which recommended in the system description.
Constraints related to soil mineralogy
High leaching potential (e): Soils with a low cation exchange capacity (CEC) have topsoils withlow organic matter content, low clay content, clay minerals with low CEC, or all these properties.
These soils have a low inherent fertility and also a low capacity to retain nutrients added as
fertilizers.
High phosphorus fixation (i): This is caused primarily by a high content of free ferric oxides(Fe2O3) in the clay fraction, which fix phosphate ions. It is a feature also found in strongly acidsoils, and hence commonly associated with aluminum toxicity. High P fixation by Fe; P
deficiency; Fe toxicity potential; these soils are difficult to puddle and will regenerate to their
original structure rapidly.
Low Nutrient Capital Reserves (k): Low inherent fertility because of low inherent reserves ofweatherable minerals; potential K deficiency depending on base contents of irrigation water.
Low organic matter status (o): N deficient; response to N fertilization very likely; low ECEC on
sandy soils; N fertilizer should be applied in frequent, small doses.
Low inherent P content (p): Plant available P deficient; response to small additions of P
fertilization.
Constraints related to soil reaction
Al toxicity, low pH (a, a-): Aluminum toxicity will occur in aerobic layers; these are soils in which
the exchange complex is dominated by alumina. The problem is strongly acid soils, which can becaused by strong leaching from high rainfall, and mainly from oxidation of sulfidic material.
Actual acid sulfate soils (c, c-): Al and Fe toxicity, low pH, and P deficiency, which originatedfrom oxidation of sulfidic material.
Potential acid sulfate soil (f, f-): Potential acid-sulfate soils, causing Fe and S toxicity whenanaerobic and Al toxicity when aerobic; depth at which sulfidic material occurs determines
feasibility of rice production; Zn deficiency common; prevent seepage from these areas.
Constant saturation (g+): Prolonged submergence causes Zn deficiency. N loss increased if soil isintermittently flooded and drained.
Saline (s, s-): Defines saline soils; drainage needed but EC of irrigation water must be considered. .
Potential Sodic (n-): This soil has a slightly high content of sodium but is low in calcium andmagnesium salts causing soil dispersion, puddling, poor infiltration and poor aeration, and if
sodium is high in the plow layer, probability of surface crust formation will be increased
METHOD FOR RICE SOIL FERTILITY CLASSIFICATION
Based on the soil constraints for rice cultivation, a method for rice soil fertility classification related
to constraints recommended, on the basis of FCC system from Sanchez et al (2003) with somemodifications, which are easy to apply and classify by using the simple methods for identificationin the field or laboratory.
The   term   “FCC”   is   used   to   indicate   adaptation   of   the   Fertility   Capability   Classification,   as  developed by Sanchez and Buol (1985), and modified by Sanchez et al (2003), to the soil and rice
growing conditions, which deal with soil morphology, soil physic, and soil chemistrycharacteristics. Most of class limits are borrowed from Soil taxonomy (Soil Survey Staff, 1994) or
the FAO/Unesco soil classification system (FAO, 1974). The system consists of two categorical© ISERD

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IJERD – International Journal of Environmental and Rural Development (2011) 2–1

levels. The first category; type/substrata/subsoil type - describes topsoil, substrata and subsoil
texture at three soil depths and is expressed in capital letters. The second category; condition
modifiers defined to delimit specific soil conditions affecting rice growth with quantitative limits.
Each condition modifier is expressed as a lower case letter. The type/substrata type/subsoil typeand condition modifiers are the soil attributes in terms of their capability for rice plant growth.
Emphasis is placed on features that are easily detectable in the field, such as texture, color, depth ofhorizons, presence or absence of mottles, etc. Soil analytical laboratory data are only used tosupport the classification if available. This approach was chosen to enable people with little
practical experience in pedology to easily identify soils in the field and classify them into one of
the broad groups or phases.
Based on the FCC structure from Sanchez et al (2003), modifiers from system were used forrice soil. Based on the FCC structure from Sanchez et al (2003), modifiers from system were used
for rice soil. We found the new structure system that can be used for classifying rice soils. Fourteen
soil modifiers that affect rice growth were determined: a, a-, c, c-, e, f, f-, g+, i, n-, s, s-, o, and p.
Among these parameters, a, a- ,e , g+, i , k, n-, o, p, s- for topsoil type, (which directly affects riceroot), and a, a-, c, f, g+, k, i, s, s-, n-, for substrata type, which directly affects rice root, and c-,f - , s,s- for subsoil type. There were 6 modifiers added to the system from Sanchez et al (2003), such as:p, o, c, c-, f, f-, in which superscripts + or - indicate a greater or lesser expression of the modifiers.
The structure of the soil names in the system were changed as follows: Soil texture of topsoil
layer 0 to 20cm (C, L) plus modifiers of topsoil layer (a, a-, e, i, k, g+, n-, o, p, s-) plus soil textureof substrata topsoil; 20 to 50cm (C, L) plus modifiers of substrata topsoil (a, a- ,c ,f ,g+ ,k ,i, s ,s- ,n-),plus texture of subsoil 50 to 100cm (C, L, S), plus modifiers of subsoil layer (c-, f-, s, s-). The
pertinent parts of the classification, which have relevance to rice growing, are described below.
System description
Type (Textute) at less than 20cm
L : Loamy : <35% clay but not loamy sand or sand.
C : Clayed : > 35% clay;
Modifiers:a : Soil pHH2O(1:1) < 5.0 (or > 60% Al saturation),a- : Soil pH
from 5.0 to 6.0 (or 10-60% Al saturation).
H2O(1:1)e : < 4 cmolc kg-1 soil as ECEC, or < 7 cmolc kg-1 soil by sum of cations at pH 7, or < 10 cmolc
3+
kg-1 soil by sum of cations +Al +H+ at pH 8.2
k : Exchangeable K < 0.2 meq/100g soil, or coarse texture (sandy) .
g+ : Prolong submergence more than 200 days/year, soil without clearly mottles represented forFe3+ from less than 20cm.
n- : Soil ESP from 6 to 15%.
o : < 0.75% Organic Carbon, and applied for top soil only.
p : (Applied for surface soil only). Available P < 2mg/100g (Olsen), or < 1mg/100g (Bray II).
s- : ECe 2 - 4 mmhos/cm at 25oC.
(Above types and modifers should be applied in this layer only)

Substra type (Textute) at 20 to 50cm
L : Loamy, <35% clay but not loamy sand or sand;C : Clayed, > 35% clay
Modifiers:
a- : Soil pH
from 5.0 to 6.0 (or 10-60% Al saturation).
H2O(1:1)

a : Soil pHH2O(1:1) < 5.0 (or > 60% Al saturation)c : Soil pHH2O(1:1) < 3.5; Jarosite mottle with hue = 2.5Y or yellower, chroma 6.
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f : Sulfidic material; pH < 3.5 after drying, without jarosite mottle with hue = 2.5Y at < 50 cm.
i : > 4% free Fe; or mottle with hue redder 5YR which > 35% clay.
k : Exchangeable K < 0.2 meq/100g soil, or coarse texture (sandy)g+ : Prolong submergence more than 200 days/year, soil without clearly mottles represented forFe3+ from 20cm to 50cm.
n- : Soil ESP from 6 to 15%.
s- : ECe 2 - 4 mmhos/cm at 25oC.
s : ECe > 4 mmhos/cm at 25oC.
(Above Substrata types and modifers should be applied in this layer only)

Subsoil type (Textute) at 50 to 100cm
S : Sandy, loamy sands and sands
L : Loamy, <35% clay but not loamy sand or sand;C : Clayed, > 35% clay
Modifiers:c- : Soil pH< 3.5; Jarosite mottle with hue = 2.5Y or yellower, chroma 6.
H2O(1:1)

f- : Sulfidic material; pH < 3.5 after drying, without jarosite mottle with hue = 2.5Y at > 50cm soil
surface.
s : ECe 2 - 4 mmhos/cm at 25oC.
s : ECe > 4 mmhos/cm at 25oC.
(Above Subsoil types and modifers should be applied in this layer only)Interpretation of system nomenclature
The whole idea of this  system  is  that  the  soil  ‘name’  as  given  by its system is meaningful for soil
fertility management.
CAPITAL character: indicated for TYPE, SUBSTRATA TYPE, SUBSOIL TYPE according
to soil depth.
Normal character: indicated for Modifiers and follows after above character
Example: Soil profile which has silt texture (L) at < 20cm, silt (L) and clay (C) at 20-50cm, and50-100cm, and modifiers a, p at surface and a, c, i at subsurface and f-, s- at subsoil, which can be
named as LapLaciCf-s-.
Strategies for better utilization of soil and soil fertility conservation
The management requirements are given per interpreted soil property or group of properties. A
complete listing of all possible combinations is not given because only a limited number of
combinations of soil properties will be found in any area under consideration. On a large scale,
however, interpretation of the soil properties in relation to farming systems, local expertise or rice
varieties could be a valuable extension tool. The management requirements are based on Sanchez
et al (2003), Smith (1989) and several experiments in the Mekong delta, Vietnam, on soil
reclamation, etc. A description of each soil fertility or management constraint identified is given
below.
Al toxicity, low pH (a, a-): Soluble and exchangeable acidity should be removed as much as
possible by leaching before applying amendments.
Actual acid sulfate soils (c, c-): The free sulfuric acid dissolves clay minerals and produces large
amounts of exchangeable aluminum. Iron and manganese toxicities and phosphorus deficiency arecommon. Physical properties are very poor. Jarosite occurs at 10 to 50 cm depth (c). Draining
results in a dramatic decrease in pH. High liming rates (greater than 10t/ha every 3 to 4 years) or
long term leaching would then be required for crop production (Breeman and Pons, 1978). The© ISERD

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most profitable practice is shallow drainage to grow one crop of a medium-term rice (Vo-Tong
Xuan, 1997).
High leaching potential (e): The use of mineral fertilizers is not recommended in these soils intheir natural state, as nutrients are not retained by these soils due to the low capacity to retain
nutrients. In addition, leaching causes big nutrient losses when lime and fertilizers are applied;therefore, heavy applications of these nutrients and of N fertilizers should be split. Organic matter
application is also recommended to increase soil cation exchange capacity. The practicality ofadding high activity clays to increase permanent charge could be assessed (Noble et al., 2004).
Potential acid sulfate soil (f, f -): When f soils are exposed to air and are low in calcium carbonate,
FeS2 is oxidized to ferric sulfate and free sulfuric acid, producing pH values on the order of 2 or 3.
Drained acid sulfate soils are extremely infertile. Flooded rice is often grown, since underconstantly reduced conditions, the pH is sufficiently high to eliminate aluminum toxicity.
High phosphorus fixation (i): These soils require high levels of P fertilizers or special P
management Sources and a method of P fertilizer application should be considered. P fertilizer
application should be split into several times as recommended by Đỗ Thị Thanh Ren and Nguyễn
Mỹ Hoa (1998).
Low Nutrient Capital Reserves (k): Potassium fertilizers must be added. Generally, these soils
have also limited capacity to retain nutrients and the potassium, calcium and magnesium added canbe easily lost (Nguyễn Mỹ Hoa, 2003). The other source of nutrient capital reserves is soil organic
matter, which contains all the nitrogen and much of the phosphorus and sulfur capital of soils.
Potassium fertilizers or organic amendments with a significant content of K will need to be applied.
Crops should be closely monitored for K deficiency symptoms (P. M. Moody et al, 2008).
Prolong submergence (g+): Prolonged submergence causes Zn deficiency, especially on all year
round cultivation soil remittently flooded and drained. H2S toxicity symptom can occur if soil highin organic matter (Ponnamperuma, 1977)
Potential Sodic (n-): Reclamation requires the replacement of Na+ on the exchange complex by
Ca2+ and leaching of Na+ out of the root zone. Soil permeability and internal drainage must also be
improved, so the displaced sodium ions can be leached out of the root zone.
Low organic matter status (o): Increasing the levels of organic matter in these soils would
improve nutrient supply, increase CEC and water holding capacity. The management of soilorganic   matter   involves   mulching   and   incorporation   of   ‘green   manure’   crops,   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 organic wastes obtained
from off-site (P. W. Moody et al, 2008).
Low inherent P content (p): P management should be considered as a long-term investment insoil fertility, and it is more effective to prevent P deficiency than to treat P deficiency symptoms,
because P is not easily lost or added to the root zone by biological and chemical processes that
affect N supply. The residual effect of P fertilizer application can persist for several years, andmanagement must emphasize the buildup and maintenance of adequate soil-available P levels toensure that P supply does not limit crop growth and N use efficiency. Use rice cultivars that use P
efficiently.
Saline (s, s-): Presence of soluble salts requires drainage and special management for salt-sensitive
rice varieties. Total reclamation of saline soils is often impractical because of the lack of highquality water for irrigation and leaching. Wetland rice production may be an economical alternative.
Continuous flooding helps to leach salts out of the root zone. Where enough irrigation water ofgood quality is available, salts can be leached unless there are high percentages of sodium in thesoil which will result in structure collapse and pan formation (Sombroek and nachtergaele, 1994).
Limitations of the method
Land use recommendations and soil improvement/reclamations were based on field survey, farmer
interview and several field, lab experiments from several authors recommended, which needs to betested and recommended for specific location. Modifiers on soil biology as recommended by© ISERD

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Sanchez et al (2003) is need to be added. Besides rice cultivation, other crops such as vegetable,
upland, aquaculture, etc, were integrated to rice cultivation, since the system did not classify orrecommend for all systems. There are some gaps in defining and identifying the indicators or
modifiers. The developed system is used for classification of rice soil fertility at specific locations
only.
CONCLUSIONS AND RECOMMENDATIONSThe soil fertility classification relies mostly on the topsoil and subsoils properties that indicate thesoil fertility capability and affect rice production. The classification allows no specialists to classify
the soil on which they are standing, in the field, even without the aid of a laboratory. The key to thesuccess of the system will be its usefulness to agriculturalists or soil scientists working in the field.
The results are the first attempt to compare soil constraints using standardized data andmethods. In order to develop sustainable systems, there must be reliable information on theconstraints and potential of the soil and land resources. The principles of soil management are wellknown, but because climatic, soil and water conditions vary so widely, the design of land use
systems, and particularly of conservation measures, must be site-specific. Details of the system fordifferent levels of classification and recommendation should be studied for proper recommendation.
If a soil cannot be adequately classified, or depending on the scale of study, then it is possible
to  create  a  new  phase  or  modifiers,  because  the  system  has  been  left  “open-ended”  to  accommodate  such modifications in the future, which can be classify the soil for better management and forgetting more crop productions. There are some relations between modifiers definition with soil
diagnostic horizons, properties, materials from FAO-WRB (World Reference Based) system, so itneeds to study on those relationships for conversion from soil map to soil fertility map.
REFERENCES
Breeman, N.V. and Ponts, L. (1978) Acid sulfate soils and rice. Soils and Rice. International Rice ResearchInstitute, 739-763, Philippines.
Buol, S.W., Sanchez, P.A., Cate, R.B. and Granger, M.A. (1975) Soil fertility capability classification, A
technical soil classification system for fertility management. Soil Management in Tropical America,
North Carolina State University, Raleigh, 126-145, USA.
FAO (1974) A framework for land evaluation. Soils Bulletin 32. FAO of the United Nations, Italy.
FAO (1995) Digital soil map of the world and derived soil properties. FAO, Rome.
Nguyễn Mỹ Hoa (2003) Soil potassium dynamics under intensive rice cropping. A case study in the Mekong
Delta, Vietnam. Ph.D thesis Wageningen University, Netherlands.
Noble, A.D., Ruaysoongnern, S., Penning de Vries, F.W.T., Hartmann, C. and Webb, M.J. (2004) Enhancing
the agronomic productivity of degraded soils in northeast Thailand through clay-based Interventions.
ACIAR Proceedings, 116, 147-160.
Moody, P.W., Legrandl, P.T.J. and Chon, N.Q. (2008) A decision support constraints to upland soils. Soil
Use and Management, 24, 148-155.
Ponnamperuma, F.N. (1977) Screening for tolerance to mineral stresses. International Rice Research Institute,
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Sanchez, P.A., Palm, C.A. and Buol, S.W. (2003) Fertility capability soil classification: A tool to help assess
soil quality in the tropics. Geoderma, 114, 157-185.

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