Departamento de Biologia Vegetal, Facultad de Farmacia,Departamento de Biologia Vegetal, Facultad de...

Land evaluation methodology for Mediterranean

environments

C. Ano, J. Sanchez & C. Antolm

Departamento de Biologia Vegetal, Facultad de Farmacia,

Universitat de Valencia, 46100 Burjassot (Valencia), Spain.

Abstract

Land Evaluation in Spain experienced a late development and, above all, its evolution has beenhighly dependent on the most significant international methodologies. These characteristics haveresulted in the current lack of a methodological frame suitable for the biophysical characteristicsof the Mediterranean region. We propose a new methodology that fills this gap and provides anevaluation system which considers the special characteristics of our soils and the environmentalproblems of the Mediterranean agricultural lands. The edaphic resource is studied from a holisticpoint of view, and several stages are distinguished in the evaluation process. Firstly, a set ofintrinsic and extrinsic soil characteristics is selected and ranked. Secondly, parameters areassessed and grouped into two Indexes, namely Capability and Vulnerability, which are thecorner stone of this methodology. The Capability Index refers to the intrinsic vocation of bothsoil and its physical surrounding, and it determines land capability for farming use. TheVulnerability Index shows the potential limitations on land use due to human action. The effectsof these limitations are, either the deterioration of the edaphic system functions or themodification of its properties.

1 Introduction

The soil is a fundamental attribute of natural ecosystems in two ways. First, it isa multifunctional system ( productivity, scene of human activities, regulation ofthe hydrological cycle, control of pollutant substances, etc ). Second, it is a verylimiting resource when inadequately used. Thus, the soil is a key element in theplanning and management of natural resources. Evaluation procedures used inApplied Edaphology efficiently assess the edaphic potential. Land evaluationsystems determine those characteristics that make the soil either capable of, orvulnerable to sustaining human activities. According to the methodologicalapproach, they allow to appraise the soil potentials and limitations, as well as toprovide feasible plans for the use of lands. As land evaluation systems integrateknowledge of the enviromental resources, they participate in land-use planningfrom its very first stages (Vink, 1983).

There exist many international methodologies that establish the soilcapability or suitability, either for general kinds of agricultural purposes or for

Transactions on Ecology and the Environment vol 16, © 1997 WIT Press, www.witpress.com, ISSN 1743-3541

490 Ecosystems and Sustainable Development

specific uses accurately described. In Spain, application of the evaluationapproaches of the most internationally widespread and accepted methodologies(Klingebiel and Montgomery, 1961; Riquier et al., 1970; F.A.O., 1976) has provedto be insatisfactory because, as a general rule, these methodologies focused on aspecific problem, difficult to extrapolate to our area. Their adaptation to localconditions is rarely succesful, especially if the criteria are wrongly selectedfrom the beginning, and if limits for the gradation of factors are not modified(Ario, 1996). Therefore, we claim the need for specific land evaluationprocedures adapted to the characteristics and necessities of a particular area, inorder to determine its soils capability or suitability.

Thus, we have developed a land evaluation methodology adapted to theparticular environmental characteristics of the Valencian Community and moregenerally, of the Mediterranean lands. Summing up, we have created amethodology (Ano, 1996) which analyses the performance of soil mappingunits of a particular area, evaluating -through two proposed Indexes, Capabilityand Vulnerability-, the soil potentiality and fragility with regard to major kindsof agricultural uses in the Mediterranean countryside. According to the valuesresulting from application of both Indexes, we assignate the Land UseRecommendations, a final proposal that sets up the most suitable kind of landuse for every mapping unit of the area under evaluation. Next, we develop thefirst two stages of our methodology: gradation of intrinsic and extrinsic soilparameters, and their appraisal and grouping into two Indexes whichrespectively illustrate the soil Capability and Vulnerability.

2 Evaluation of the edaphic potential: parameters

A first stage, basic for land evaluation, is the selection of a group of intrinsic andextrinsic soil characteristics in order to assess the soil capability and the soilvulnerability to degradation. These characteristics take shape in some parameters,establishing a gradation in every one of them. Intervals for every parameter havebeen established according to the peculiar characteristics of the Mediterraneanenvironment.

Thermic Conditions (C) and Plant-Available Soil Water (W) are twoparameters that directly affect plant growth, conditioning land use. The firstparameter (Table 1) is appraised according to the length of the vegetative season(Euverte's formula: number of months with an average temperature above 10-C),the period with a risk of freeze (Emberger's formula: number of months with anaverage temperature below 7 C), the value of the minimum absolute temperatures inwinter and the frequency of freeze in spring. The statistical information is availablein Perez Cueva, 1994. In the second parameter (Table 2), as it is difficult to establishthe field capacity and the permanent wilting point for every Mediterranean type ofsoil (the water holding capacity greatly varies among different soils) we havedecided to carry out a qualitative evaluation in terms of the soil water balance andthe presence, absence or easy access to surface or ground water resources, asassessed from hydrologic reports. The statistical information used to determine thesoil water balance (mean monthly rainfall, useful available water and mean monthly


Ecosystems and Sustainable Development 491

potential evapotranspiration according to Thorntwaite) comes from Perez Cueva,1994. The Risk of Flooding (F) parameter indicates the approximate frequency ofoccasional flooding caused by torrential rains. To establish the parameter gradationwe have used the criteria established to create a Geoscientiphic Cartography in theValencian Community, where a mixed geomorphological-historical method hasbeen used by incorporating the analysis of the flooding historical record (Table 3).

Cl. Very Appropriate Thermic ConditionsContinuous or long vegetative period (vegetative season longer than 10 months)Freezing risk shorter than 3 monthsMinimum absolute temperatures in winter are not below -4-CNot very common freezing in spring

C2. Moderately Appropriate Thermic ConditionsMedium vegetative period (vegetative season between 8 and 9 months)Freezing risk between 4 and 5 monthsMinimum absolute temperatures in winter are often below -5-CCommon freezing in spring

C3 Little Appropriate Thermic ConditionsShort vegetative period (vegetative season shorter than 7 months)Freezing risk longer than 6 monthsMinimum absolute temperatures in winter are often below -10-CVey common freezing in spring

Table 1. Thermic Conditions (C). Gradation.

Wl High Plant-Available Soil WaterSoil water deficit is minimum, or it does not occur in decisive moments for plantgrowing. If there is a high deficit, it is mitigated by plenty of surface or ground waterresources or with an easy access to them.

W2. Moderate Plant-Available Soil WaterSoil moisture balance determines the yield level of some specific crops. Surface orground water resources are limited or they have moderate difficulties to be used.

W3. Low Plant-Available Soil WaterVery severe water deficit that affects the growing and the yield level of any kind ofcrop. Surface or ground water resources are limited, with a very difficult use or witha low profitable economic access.

Table 2. Plant-Available Soil Water (W). Gradation.

FO! Seasonally or permanently flooded areas.Fl Low flood hazard. Flooding occurrence in time spells longer than 25 yearsF2 Medium flood hazard. Flooding occurrence in time spells between 10-25

yearsF3 - High flood hazard. Flooding occurrence in time spells shorter than 10 years

Table 3. Risk of Flooding (F). Gradation.



The Slope parameter (P) has a strong influence on many edaphic properties.Slope characteristics either allow or prevent mechanization and irrigation practices(Table 4). The Effective Soil Depth (X) parameter refers to the soil depth at whichroot growth is strongly inhibited. The gradation indicates the higher or lower soilcapacity to provide a suitable environment for plant rooting, water retention andnutrient supply (Table 5).

PIP2

P3

P4

P5

P6

Flat. Intensive mechanization and irrigation. No limitations.Gentle. High potential of mechanization. Moderate capability forirrigation.Moderate. Medium potential of mechanization. Low capability forirrigation.Moderately steep. Low potential of mechanization. Very lowcapability for irrigation.Steep. Very low potential of mechanization. Very severelimitations.Very steep. Marginal. Extremely severe limitations.

<3%3-8%

8-15%

15-25%

25-45%

>45%Table 4. Slope (P). Gradation.

Xlijjpft Deep. No limitations.Moderately deep. Slight limitations.Shallow. Moderate limitations.Very shallow. Severe limitations.Extremely shallow. Very severe limitations.

10-

Table 5. Effective Soil Depth (X). Gradation.

The Chemical Properties (Q) parameter indicates the higher or lower chemicalfertility of the soil, showing the facility of the soil to supply mineral nutrients to theroots. This aspect does not depend as much on the nutrients quantity as on certaincharacteristics, very difficult to be modified, that directly affect the availability. Theavailability depends on the organic matter content, the cation exchange capacity, thepH and the proportion of calcium carbonate and active limestone. Thesecharacteristics are assessed together (Table 6).

;gp|ppjpil:J:;piy;: Ql.:VriyJ ApproO.M. (%)

10-20Act.Lim.(%) C.E.C.(cmol(+)/kg)

<5 >20 6.1-7.8

1-2 20-30Act.Lim(%)

5-10C.E.C.(cmol(+)/kg)

10-20 5.5-6.1/7.8-8.5nQ3; Inappropriate Chemical Prbjj&Hie

30-50Act.Lim(%)

10-15C.E.C.(cmol(+)/kg)

<10 <5.5/>8.5Table 6. Chemical Properties (Q). Gradation.



In the Stoniness (G) parameter, two different elements have been considered:rough elements bigger than 10 centimetres diameter, generally found on the surface,and smaller elements that appear in the whole soil profile. In the first case, thedifferent degrees reflect the difficulties that can be imposed on the farming activitiesby the factor. In the second case, we have considered the effects on soil physicalproperties, mainly the likely decrease of available soil for root development andnutrient and water retention (Table 7). The Rock Outcrops (R) parameter indicatesthe percentage of the soil surface continously covered by solid rock or by roughelements bigger than 25 centimetres diameter. The gradation has been carried outtaking into account the difficulties that can be imposed on the farming activities bythe factor, especially in the use of machinery (Table 8). Furthermore, we show insmall letters the distance between rock outcrops according to the criteria establishedby FA.O. (1990): class a (>50 m), class b (20-50 m), class c (5-20 m), class d (2-5m) and class e (<2 m).

;G.I-!!;G2iih

!G3i!{;G4!iiGSiii

Very slightly stony. No limitations.Slightly stony. Slight limitations.Moderately stony. Moderate limitations.Very stony. Severe limitations.Extremely stony. Very severe limitations.

'<5%mmi

5±15%mi15~40%!ni:40 80 %:liii

:>80#!!HfTable 7. Stoniness (G). Gradation.

;Riii•R21I.mill!R4.«ilR5lh

'R6.il! ;

None or very few. No limitations.Few. Slight limitations.Common. Moderate limitations.Many. Severe limitations.Abundant. Very severe limitations.Dominant. Extremely severe limitations.

!<2%|Ip2-5. 115-15%!!15f40%40-80%;>80#i!!J!

Table 8. Rock Outcrops (R). Gradation.

In the Textural Class (T) parameter, relative proportion of mineral constituentsclassified according to their size (sand, silt and clay), we establish the gradation interms of the textural properties and characteristics (i.e. higher or lower nutrient-holding capacity; water holding capacity; infiltration rate; risk of surface crustformation...) which determine the soil behaviour (Table 9).

(ayjllillllliili T2. Silty Clay Loam|||#|#||E#i 13. Sandy ClaylilllEillBliSB T6, Silt

ImBlllmllllllllllllBlilBI T9. Sand

l|T2.:Saridy aayjjoam!j|

.•Sandy]Qpa'#|||i^

Table 9. Textural Classes (T). Gradation.

The Hydromorphy (H) parameter refers to the kind of drainage (higher or lowerdegree of soil saturation) regardless the frequency and length of the saturationperiods. The use of this parameter let us distinguish between well-drained soils and



those where a poor drainage, brought about by slow permeability or a shallow watertable, determines the seasonal or permanent soil saturation (Table 10).

HI Good drainage. Presence of hydromorphic properties deeper than 50 cm.H2 Somewhat restricted drainage. Presence of hydromorphic properties

between 30-50 cm depth.H3 Poor drainage. Presence of hydromorphic properties above 30 cm depth.

Table 10. Hydromorphy (H). Gradation.

Gradation in the Salinity (S) and the Alkalinity (N) parameters has been carriedout according to the limiting effects that the presence of salts more soluble thangypsum or sodium ion has on farming. In the first case, salt concentration isexpressed in terms of the electrical conductivity (25-C) of the solution extractedfrom a saturated sample of soil (Table 11). In the second case, it has been provedvery convenient to express the alkalinity level in terms of the sodium adsorptionratio (SAR) in the soil saturation extract (Table 12).

isii!!S2|1H::HHH:;

;##

IS4#issm;

Very low. No limitationsLow. Slight limitations.restrictedModerate. Moderate limiHigh. Severe limitations.Very high. Very severecrops yield satisfactorily.

. Salinity effects mostly negligible.Yields of very sensitive crops may be

tations. Yields of many crops restricted.Only tolerant crops yield satisfactorily.limitations. Only a few very tolerant

:<2'asM#izBZdg/mil;

;4rS!dS/m!i841(Jas/m>16dS/mmi

Table 11. Salinity (S).Gradation.

Nl ::•••.N2 :'*•*•N3N4'N5

Very low. No limitations.Low. Slight limitations.Moderate. Moderate limitations.High. Severe limitations.Very high. Very severe limitations.

<:5 mmol(l)l/2mii|H5-8 mmol (l)l/2##i8-11 mmol (1)1/2%11-15 mmol (1)1/2>15 mmol (1) 1/2 !#

Table 12. Alkalinity (N). Gradation.

Nowadays, Mediterranean soils present low or moderate salinity or alkalinitylevels, but topography (location on flat or gently undulated areas) and climaticconditions (low and irregularly distributed rainfall and high evapotranspiration rate)may increase current levels. Furthermore, the geological substratum and the use ofsaltpetrous or sodium ground water for agricultural purposes increase the risk, evenfor surrounding soils with very low current levels. These circumstances increase theRisk of Salinization or Alkalinization (RS/RN) in a medium or long term.Qualitative appraisal of this kind of degradation has been made in terms of thetopographical location, the water table depth, the maintenance of the irrigation anddrainage system, the leaching necessities and the agronomic quality of the irrigationwater (Table 13). These characteristics have been used by Boixadera and Porta(1991) in their methodology.



*: RS1-RN1: Low Risk of Salinization or Alkalinizatlon1|i|p||l||||J;Presence of a saline water table (>150 cm) that does not affect soils along the year.Very good maintenance of the irrigation and drainage system. Optimun levelling inthe land to be watered. Little leaching needs which are totally meet by irrigation.No risk of toxicity caused by Na, Cl or B. ^^j|lPl!!llpRS2 RN2; Moderate Risk of Salinization or Alkalinizationii|§§||Presence of a saline water table between 100 and 150 cm. Good maintenance of theirrigation and drainage system. Good levelling of the land to be watered. Highleaching necessities are not entirely meet by irrigation. Likely salinity increase. SoilSAR between 10 and 15. Moderate risk of toxicity caused by Na, Cl or B.

RS3 -RN3. High Risk of Salinization or Alkalinizatiori jjjjjPresence of a saline water table no deeper than 100 cm. Bad maintenance of theirrigation and drainage system. Faulty levelling of the land to be watered.Extremely high leaching necessities imposible to meet by normal irrigationpractices. Likely high increase of salinity levels. Soil SAR >15 . Medium or highrisk of toxicity caused by Na, Cl or B.

Table 13. Risk of Salinization or Alkalinization (RS/RN). Gradation.

The Present Erosion (Ea) degree indicates the approximate soil loss underpresent environmental conditions. The Potential Risk of Erosion (Ep) reflects thelikely soil loss if some conditions affecting the process change (potential soilcredibility, removal of the present vegetation cover and abandonment of supportpractices). We made a quantitative assessment (Table 14) applying the UniversalSoil Loss Equation, modified for the Mediterranean area by Rubio et al. (1984).Furthermore we made a qualitative assessment, by analysing the morphologicalchanges resulting from the erosive processes (sheet erosion, rills, gullies, ravines andlandslides) and considering the proportion of the land surface affected by them inevery case.

Eal-EplEa2-Ep2Ea3-Ep3Ea4-Ep4Ea5-Ep5Ea6-Ep6

* F"7 •JLjil

LowSlightModerateHighVery HighExtreme

<5 tm/ha/yr5-10 tm/ha/yr10-25 tm/ha/yr25-50 tm/ha/yr50-100 tm/ha/yr>100 tm/ha/yrT ithir» ff">F)£icp

Table 14. Present degree of erosion. (Ea). Potential risk of erosion. Gradation.

The Soil Vulnerability to Pollution (V) parameter refers to soil degradationbrought about by human action. The parameter gradation is carried out according tothe methodological approach established by Schmidt (1991) and modified for theMediterranean area by Sanchez and Ario (1993). We established the assessmentaccording to the clay and organic matter content and the textural class(characteristics accounting for the adsorption capacity of the A horizon), the water



holding capacity (that shows the leaching potential) and the slope that determinesthe higher or lower motion of chemical substances by surface runoff (Table 15).

DJ wiSoil PolJutioE

Clay(%) O.M.(%) Texture Moist.Cap.(mm) Slope(%)<8 <1.5 T8/T9 <100 >7

Clay(%) O.M.(%) Texture Moist.Cap.(mm) Slope(%)8-18 1.5-3 T5/T7 100-200 3-7

Clay(%) O.M.(%) Texture Moist.Cap.(mm) Slope(%)>3 T3/T4 >200 <3

Table 15. Soil Vulnerability to Pollution (V). Gradation.

These parameters are grouped into two Indexes that show the soil capability leveland the kind and degree of present and/or potential limitations for land use.

3 Capability Index and Vulnerability Index

The Capability Index comprises the following parameters: slope (P), plant-available soil water (W), thermic conditions (C), risk of flooding (F), rockoutcrops (R), stoniness (G), effective soil depth (X), hydromorphy (H),chemical properties (Q), textural class (T), salinity (S), alkalinity (N) andpresent erosion (Ea). This Index shows the soil intrinsic vocation which willeither allow or prevent land agricultural uses. Therefore, it should determine theway of man's use in every evaluation unit. In this way, the Capability Index,along with the Vulnerability Index will condition the final proposal of land use.According to the values assigned to every parameter, we distinguish amongdifferent degrees of Capability: Very High, High, Moderate, Low and VeryLow.

Very High Capability (Cl): Parameter values never exceed 1, except fortextural class, chemical properties, stoniness and risk of flooding, which mayreach a value of 2.

High Capability (C2): Parameter values are never above 2, except fortextural class, stoniness and risk of flooding which may reach a value of 3.

Moderate Capability (C3): Parameter values never exceed 3, except for thestoniness and the textural class, which may respectively reach values of 4 and 7.

Low Capability (C4): Values of the following parameters: slope, effectivesoil depth, rock outcrops, stoniness, present erosion, salinity, alkalinity andsandy textural class, range between 3 and 4, but textural class and slope mayrespectively reach values of 9 and 5. Values of remainder parameters are notsignificant.

Very Low Capability (C5): The most significant parameters are: slope,effective soil depth, stoniness, present erosion, salinity, alkalinity and sandytextural class. More of two of them reach a value of 5. Values of remainderparameters are not significant.



The Vulnerability Index includes the following parameters: potential risk oferosion (Ep), risk of salinization or alkalinization (RS/RN) and soilvulnerability to pollution (V). It refers to a set of limitations that restricts thenumber of possible ways of land use. This Index shows the easy manner inwhich human activities (inadequate practices or lack of efficient controlmeasures) may modify soil properties and/or reduce or damage the ecologicaland agronomic functions (protection against exogenous processes, biomassproduction), that a particular kind of soil can develop. According to the valuesassigned to the three parameters, we distinguish among Low, Moderate andHigh Vulnerability, which refer to different degrees of soil protection.

Low Vulnerability (VI): All parameter values are low (RS1-RN1, VI, Ep2/3).

Moderate Vulnerability (V2): All parameters have medium values (RS2-RN2, V2 and Ep 4).

High Vulnerability (V3): High or very high parameter values (RS3-RN3,V3 and Ep 5/6).When there are not limiting factors in both Indexes, the range of possible

uses of land increases. On the contrary, this range diminishes when there existlimitations, and mainly when they bring about a potential or actual soildegradation. As a general rule, a soil suffering from severe physical limitationshas few feasible uses. Analysis of those properties considered as unfavourableallows thinking about the necessary improvements to be made, the difficultiesinvolved in their elimination and the need of treatments for sustained land use.

4 Conclusions

The appraisal of both extrinsic and intrinsic soil characteristics which arerepresented in a number of parameters, allows a first approach (qualitative andquantitative values) to the capability and vulnerability of soils. In this firststage, unlike in traditional evaluation systems, we consider all the parametersthat have been selected, by presenting all the values given to the differentfactors, even if they are not very significant. In this way, a loss of information isavoided and the whole set of basic data obtained during the evaluation processis within the user's reach. The thorough analysis of every parameter, whichresults in the attribution of individual values, allows to ascertain whichparameter is more significant in every particular case, showing the occurrenceor absence of undesirable properties and specifying the degree of limitation forland use.

The assemblage of parameters in the Capability and Vulnerability Indexessynthesize all the information used to evaluate a cartographic unit, classifyingrural areas into homogeneous units with an uniform performance, which are inthe end planning units. This methodology has been applied in three areas of theValencian Community ( Chelva, Villar del Arzobispo, Sagunto ) under differentenvironmental conditions and with a different socio-economic situation.Results are available in Ano (1996). Lately, the National Plan of Environmental



Cartography has included both Indexes as elements for soil appraisal, in theproduction of soil maps useful for land evaluation and planning.

Eventually, land use will depend on political, cultural, economical and socialfactors, but knowledge of soil capability and vulnerability is needed forsatisfactory land-use planning. The soil is a scarce and non-renewableresource, at least in short or medium term, and its inappropriate use may haveserious effects, especially on the Mediterranean environment, characterized by adeficient capacity of recovery of ecosystems disturbed by human action.

5 References

Ario, C. Metodologia de evaluation de suelos para el dmbito mediterrdneo,Servicio de Publicaciones de la Universitat de Valencia, Valencia, 1996.

Boixadera, J. & Porta, J. Information de suelos y evaluation catastral Metodo delValor Indice, Ministerio de Economia y Hacienda, Madrid, 1991.

F.A.O. A framework for land evaluation. Soils Bulletin 32, F.A.O., Rome, 1976.

F.A.O. Guidelines for soil profile description, F.A.O., Rome, 1990.

Klingebiel, A.A. & Montgomery, P.H. Land capability classification,AgriculturalHandbook 210, U.S.D.A, Washington ,1961.

Perez Cueva, A.J. Atlas dimdtico de la Comunidad Valenciana (1961-1990),Conselleria d'Obres Publiques i Transports, Generalitat Valenciana, Valencia, 1994.

Riquier, J, Bramao, L. & Cornet, S.P. A new system of soil appraisal in terms ofactual and potential productivity, F.A.O., Rome, 1970.

Rubio, J.L:, Sanchez, J., Sanroque, P. & Molina, MJ. Metodologia de evaluacion dela erosion hidrica en suelos del area mediterranea, pp. 827-836, / CongresoNational de la Ciencia del Suelo, Madrid, 1984.

Sanchez, J. & Aiio, C. Metodologia de Capacidad de Uso para la planificacion deusos del suelo en el ambito mediterraneo, pp. 1391-1398., XII CongresoLatinoamericano de la Ciencia del Suelo, Salamanca.

Schmidt, R. Soil vulnerability assessment and chemical soil degradation in easternGermany, pp.77-81, Proceedings of the Workshop on Mapping of Soil and TerrainVulnerability to Specified Chemical Compounds in Europe, Wageningen, 1991.

Vink; A.P.A. Landscape ecology and land use, Longman, London.


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