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Characteristics and fertility constraintsof degraded soils in Leyte, PhilippinesIan A. Navarrete a , Kiyoshi Tsutsuki b & Victor B. Asio ca United Graduate School of Agricultural Sciences , IwateUniversity , Iwate , Japanb Laboratory of Environmental Soil Science , Obihiro University ofAgriculture and Veterinary Medicine , Inada-cho , Japanc Department of Agronomy and Soil Science , Visayas StateUniversity , Baybay , Leyte , PhilippinesAccepted author version posted online: 23 Feb 2012.Publishedonline: 20 Mar 2012.

To cite this article: Ian A. Navarrete , Kiyoshi Tsutsuki & Victor B. Asio (2013): Characteristics andfertility constraints of degraded soils in Leyte, Philippines, Archives of Agronomy and Soil Science,59:5, 625-639

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Characteristics and fertility constraints of degraded soils in

Leyte, Philippines

Ian A. Navarretea*, Kiyoshi Tsutsukib and Victor B. Asioc

aUnited Graduate School of Agricultural Sciences, Iwate University, Iwate, Japan;bLaboratory of Environmental Soil Science, Obihiro University of Agriculture and Veterinary

Medicine, Inada-cho, Japan; cDepartment of Agronomy and Soil Science, Visayas StateUniversity, Baybay, Leyte, Philippines

(Received 26 February 2011; final version received 22 May 2011)

Knowledge of the characteristics and fertility status of degraded soil isfundamental to planning suitable soil management strategies for crop productionpurposes. Such knowledge can be obtained through quantitative appraisal of soilproperties and assessment of soil fertility status. Sixty soil samples were collectedfrom five locations at Ormoc, Baybay, Bontoc, Bato and Matalom on the westernside of Leyte island, Philippines. An important physical constraint in most of thesoils is the high clay content, particularly in the soils of Baybay and Bato where itis a problem for cultivation. The strongly acidic and strongly alkaline pH, lowavailable P and, in some cases, low exchangeable K are the chemical constraints.Variation in the physical and chemical constraints of these degraded soils isdirectly or indirectly related to the nature of the parent material, geomorphicposition and anthropogenic effect. Soil fertility characteristics are distinct withinsimilar soil types, primarily because they are related to the dominant soil-formingprocesses. Consideration of the soil physical and chemical constraints is essentialfor the long-term planning of soil management strategies that will lead tosustainable utilization of these problematic soils.

Keywords: degraded soils; fertility constraints; land use; Philippines; soil types

Introduction

Soil degradation, a process that lowers the capacity of the soil to produce goods orservices, is a prevalent agricultural and environmental problem in the Philippines(Asio et al. 2009). This has tremendous consequences for the important soil functionsof plant production, buffering, transformation, filtering, geogeny, cultural heritageand infrastructure (Blum 1998). The National Action Plan (NAP 2004) of thePhilippines reported that *52 000 km2 of land are seriously degraded, resulting in a30–50% decrease in soil productivity. Control of soil degradation is thus recognizedas a main research priority in the Philippines. To date, the nature and characteristicsof degraded soils in the Philippines have been poorly understood, in that there havebeen few studies on this subject (Asio 1997; Asio et al. 2009; Navarrete et al. 2009;Navarrete and Tsutsuki 2008). Utilization of degraded land has resulted in seriousecological problems (Asio 1997), low crop yield (Garrity 1993) and the failure of

*Corresponding author. Email: ian-navarrete@daad-alumni.de

Archives of Agronomy and Soil Science

Vol. 59, No. 5, May 2013, 625–639

ISSN 0365-0340 print/ISSN 1476-3567 online

� 2013 Taylor & Francis

http://dx.doi.org/10.1080/03650340.2012.663908

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forest rehabilitation projects (Alcala 1997). Cramb (2001) described that various cropproduction technologies developed for marginal areas in the Philippines have notbeen successfully adapted by farmers or have failed to alleviate crop production.Cramb further stated that the introduction of unsuitable soil managementtechnologies by farmers has intensified the soil degradation processes occurring inthese areas. Accordingly, detailed information on soil properties, which can beobtained through more pedological research, is needed for suitable land management.

Site qualities are complex collections of observable and measurable character-istics that have to be appraised for specific land uses (FAO 1976). In appraising sitequalities, several soil properties must be summarized in terms of rooting depth,rootability, moisture content, air capacity and nutrient availability (Schlichting et al.1995), including knowledge about the geomorphological and pedological historyof the landscape. Jahn and Stahr (1996) emphasized that because most soilcharacteristics are the result of soil formation or pedogenesis, the progression of sitequalities is closely related to the time-dependent development of the soil. Jahn andStahr pointed out that in land evaluation, site characteristics are elucidated as time-dependent for the duration of survey only, and this period is comparatively concisein relation to the time needed for soil formation. Because the degree of soildegradation varies immensely among sites, depending on soil forming factors, soilmanagement strategies must be location specific. This suggests that every degradedsoil has to be evaluated in terms of its properties and constraints. This will diminishthe negative ecological impact of soil degradation and may provide sound andsustainable management for these marginal lands. It was anticipated that the resultsof this study would provide knowledge for the suitable management of similardegraded areas in the Philippines. The aim of this study was to determine thecharacteristics of degraded soils in Leyte, Philippines, and to evaluate their fertilityconstraints.

Materials and methods

Description of the study area

The study area is located on the island of Leyte, Philippines, which lies between1248170 and 1258180E and between 98550 and 118480N (Figure 1). Leyte was formedfrom tectonic movement and plate convergence, which started in the Tertiary andQuaternary (Wernstedt and Spencer 1967; Aurelio 2000). Uplift and block faultingand volcanism (Scott 2000) due to the Philippine Fault that traverses the central partof the island explain the widespread occurrence of volcanic rocks, except in thenortheast and southwest of the island, where exposed limestone rocks occur. Asio(1996) explained the importance of geological uplift to the occurrence of sedimentaryrocks such as coralline limestone, sandstone, siltstone and mudstone in the northeastand southwest of the island. Mean annual rainfall is *2800 mm, which fluctuatesseasonally with a dry season from March to May (115–118 mm) and a wet seasonfrom October to January (300–403 mm). The higher annual rainfall results in goodsoil moisture conditions all year round and gives a udic soil moisture regime (SoilSurvey Staff 2006). Mean annual temperature is *288C, which is relatively constantthroughout the year. The difference between the coldest (December) and the warmest(April) months is between 2 and 38C, giving an isohyperthermic temperature regime(Soil Survey Staff 2006). According to Coronas (1920), two types of monsoon windsblow in the island and other parts of the archipelago. The monsoon known locally as

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Habagat blows from the southwest from May to October, causing extreme cloudsand rainfall on the western side of the island. From November to April, the monsoonknown locally as Amihan blows from the northwest, causing high rainfall on theeastern side of the island.

The once dipterocarp rainforests in the uplands are now patches of secondarygrowth forest and coconut plantation, whereas the lowlands are used for croplandespecially corn (Zea mays), sweet potato (Ipomea batatas) and rice (Oryza sativa).Imperata cylindrica grass is dominant in abandoned croplands, which suggest thedegraded nature of these areas.

Field description and soil sampling

Twelve well-drained soil profiles were sampled from five sites across an elevationgradient (between 97 and 735 m) on the western part of Leyte, Philippines (Figure 1).In this study, each site is referred to by their location: Ormoc, Baybay, Bontoc, Batoand Matalom, respectively (Table 1). The five profiles in Ormoc were located acrossa late Quaternary volcanic (basalt-andesite) landscape (Asio 1996; Jahn and Asio1998; Navarrete et al. 2008) at an elevation between 630 and 730 m, whereas the fourpedons in Baybay were located at an altitude of 75–112 m on a basaltic parent rock

Figure 1. Map of Leyte showing the approximate location of the study sites.

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Table

1.

Generalsite

characteristics

ofthedegraded

soilsin

Leyte,Philippines.

Location

Altitude

Studysites

Latitude(N

)Longitude(E)

(m)

Slopeposition

Parentmaterial

Soiltypea

Landuse

Orm

oc

111805.5650

124840.0960

735

Shoulder

BasaltandAndesite

Typic

Hapludand

Cultivatedland

211805.5810

124840.0520

702

Backslope

BasaltandAndesite

Typic

Hapludand

Cultivatedland

311805.6140

124840.0150

671

Middle

backslope

BasaltandAndesite

Andic

Dystrudept

Cultivatedland

411805.6430

124839.9670

660

Lower

backslope

BasaltandAndesite

Acrudoxic

Hapludand

Reforestation

511805.7510

124839.8580

666

Middle

backslope

BasaltandAndesite

Typic

Hapludand

Grassland

Baybay

610844.9050

124848.2620

112

Upper

backslope

Basalt

Typic

Hapludult

Primary

forest

710844.6880

124848.3290

107

Middle

backslope

Basalt

Typic

Hapludult

Reforestation

810844.7530

124848.2290

99

Lower

footslope

Basalt

Typic

Haplohumult

Mahoganyplantation

910844.6140

124848.1380

75

Flattoeslope

Basalt

Typic

Hapludult

Coffee

plantation

Bontoc

10

10816.7940

124849.0850

97

Upper

backslope

Corallineshale

Typic

Hapludalf

Secondary

forest

Bato

11

10819.8840

124856.5350

120

Lower

footslope

Corallineshale

Typic

Hapludalf

Secondary

forest

Matalom

12

10818.4680

124853.5310

121

Lower

footslope

Corallinelimestone

Rendollic

Eutrudept

Grassland

Note:aSoilSurvey

Staff(2006).

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(Asio 1996; Navarrete et al. 2009). The soil profiles in Bontoc and Bato have analtitude of 97 and 120 m, respectively, on a coralline shale parent material. Thecalcareous limestone soil in Matalom was located at an elevation of 121 m on agrassland field. Based on the Soil Survey Staff (2006), the dominant soil types in thestudy sites were Andisols (n¼ 18), Ultisols (n¼ 20), Inceptisols (n¼ 11) and Alfisols(n¼ 11).

Bulked soil samples were taken from every horizon of each pedon, air-dried,freed of large plant residues, ground and allowed to pass through a 2-mm wiremesh.

Laboratory analyses

Particle size distribution was determined by pipette and wet sieving methods afterpretreatment of soils with NaOAc (pH 5.0) for samples containing free carbonatesand H2O2 to oxidize organic matter (International Soil Reference and InformationCenter 1995). The pH of air-dried samples (52 mm) was measured potentiome-trically in soil/solution suspensions of 1:2.5 H2O. Organic carbon (OC) wasdetermined using a modified Tyurin method, and total nitrogen was analyzed bydry combustion using a C/N analyzer (Elementar Vario EL III, Hanau, Germany).Potential cation exchange capacity (CECpot) and exchangeable bases were measuredby the NH4OAc method (pH 7.0). Free Fe (Fed) and Al (Ald) were extracted by thedithionite-citrate and amorphous Fe (Feo), and Al (Alo) were extracted using theammonium oxalate, all according to the method described by Blakemore et al.(1987). Fe and Al in solution were determined by ICP-AES (Shimadzu ICPS-8100).Element composition was obtained by X-ray fluorescence spectrometry (Rigaku3070).

Fertility evaluation

Evaluation of soil fertility was done by matching the values of the selected soilproperty with published threshold values or conditions of the same property for cropgrowth (Landon 1991; Schlichting et al. 1995). The suitability or constraints of aparticular soil property for crop growth is expressed by a positive (þ) or negative (7)sign, where positive denotes a soil property that is favorable for crop growth orproduction, and negative denotes a soil property that is a constraint to crop growthor production, following the method used by Asio et al. (2006).

Statistical analysis

Statistical analyses were carried out using a JMP (Version 8, SAS Institute, Cary,NC, USA) software package. Significant differences between mean values of theselected soil properties were estimated by Tukey-Kramar and t-test at the 95%confidence level (p5 0.05). Multivariate analysis by principal component analysis(PCA) and hierarchical cluster analysis (HCA) were extracted from the large datasets, to classify the samples according to the values of a set of variables into principalcomponent (PC) and cluster, respectively. Prior to the PCA and HCA analysis, thedata set was mean centered and autoscaled to variance 1 to insure that all variablescontributed equally to the model, independent of the scales with which they weremeasured (Sena et al. 2002).

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Results and discussion

Soil characteristics

Because of the variety of parent materials, topography, soil types and stage of soildevelopment, the studied soils show great variations in physical and chemicalproperties (Table 2). For example, the Andisols of Ormoc, which originatedfrom volcanoclastic parent material, possess markedly higher Corg (p5 0.001),Nt (p5 0.001), Feo (p5 0.001), Ald (p5 0.001), sand (p5 0.05) and Al2O3

(p5 0.05), but markedly lower exchangeable Ca and Mg (p5 0.05) and clay(p5 0.05) compared with the other sites. Shoji et al. (1993) explained that highCorg in Andisols is due to the formation of stable complexes between organicmatter and Fe-, Al-oxides and short-range order minerals. Navarrete et al. (2008)reported that the progression of soil development at the Ormoc site is greatlyaffected by topography, because of its influence on water movement, whichdetermines the rate of weathering, run-off and soil erosion, and soil formation(Sommer and Schlichting 1997). For example, the rapid leaching of basic cationshas resulted in low exchangeable bases and an acidic nature, implying youngvolcanic soils (Shoji et al. 1993; Asio 1996; Navarrete et al. 2008). The intenselydeveloped Ultisols in Baybay (Asio 1996; Navarrete et al. 2009) have markedlyhigher contents of clay (p5 0.05), Fed (p5 0.001), CECpot (p5 0.05) and Fe2O3

(p5 0.001), and low exchangeable K and Na (p5 0.05) compared with the othersites. Based on gain and loss calculations, Navarrete et al. (2009) found that32–80% CaO, 13–75% MgO, 57–70% K2O and 34–59% Na2O have been lostthrough weathering of basalt rock into soils, and the amount of loss varies amongsoils depending on the location along the landscape. By contrast, Matalom soilhad higher soil pH (p5 0.001), silt (p5 0.05), exchangeable Ca (p5 0.001) andCECpot (p5 0.05) compared with the other sites and certainly originates from thecoralline limestone parent rock. High exchangeable Ca, CECpot and high pHsuggest the young nature of these soils. Despite similar parent material (calcareousshale) between Bontoc and Bato, the soils that developed are distinctly different.In terms of sand content (p5 0.001), SiO2 (p5 0.001) and exchangeable Mg(p5 0.001), Bato soils have significantly higher values than other studied soils.Soils in Bontoc, Bato and Matalom have significantly lower amounts of Fed(p5 0.05), Feo (p5 0.05), Ald (p5 0.05) and Alo (p5 0.05) than soils at Ormocand Baybay.

Ultisols, which comprise 33% of all samples, have appreciably higher CECpot

(p5 0.001) and contents of clay (p5 0.001), Fed (p5 0.001), Al2O3 (p5 0.001)and Fe2O3 (p5 0.001). Andisols, which comprise 30% of the studied soils haveappreciably higher Corg (p5 0.001), sand (p5 0.001), silt (p5 0.05), exchangeableNa (p5 0.05), Feo (p5 0.001), Ald (p5 0.001), Alo (p5 0.001), SiO2 (p5 0.05)and Al2O3 compared with the other soils. In addition, Andisols have appreciablylower pH (p5 0.001), exchangeable Mg (p5 0.05) and CECpot (p5 0.05). Alfisolsand Inceptisols make up another 18% of the studied soils. Alfisols have higherMg (p5 0.001), but lower SiO2 (p5 0.001), whereas Inceptisols have appreciablyhigher soil pH (p5 0.001), silt (p5 0.001), and exchangeable Ca and K(p5 0.001) compared with the other soils. The soils on Leyte, Philippines varyfrom the less-developed Inceptisols and Andisols to the well-developed Ultisolsand Alfisols.

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Table

2.

Meanvalues

ofselected

soilproperties

accordingto

studysitesandsoiltypes.

Studysite

Dominantsoiltype

Orm

oc

Baybay

Bontoc

Bato

Matalom

Alfisols

Andisols

Inceptisols

Ultisols

Soilproperties

(n¼23)

(n¼20)

(n¼5)

(n¼6)

(n¼6)

(n¼11)

(n¼18)

(n¼11)

(n¼20)

pH-H

2O

5.28c

5.41c

6.47b

5.23c

8.14a

5.79b

5.25c

6.89a

5.41bc

Corg(%

)3.03a

1.27b

1.77ab

1.07b

1.07b

1.39b

2.93a

2.12ab

1.28b

Nt(%

)0.35a

0.16b

0.19b

0.11b

0.15b

0.14b

0.30a

0.31a

0.15b

Sand(%

)40.5

a22.3

b30.3

ab

38.5

a20.6

b34.8

ab

41.43a

28.14bc

22.30c

Silt(%

)38.4

a17.6

b25.1

b15.9

b41.7

a20.10b

39.46a

38.57a

17.63b

Clay(%

)21.0

c60.1

a44.5

b45.6

b37.7

b45.09b

19.10c

33.29b

60.07a

Exch

Ca(cmolkg71)

1.06c

1.55c

5.02b

4.87b

84.97a

4.93b

0.56b

47.6

a1.55b

Exch

Mg(cmolkg7

1)

0.34c

0.98b

1.945a

1.56a

0.11c

1.73a

0.19c

0.46c

0.98b

Exch

K(cmolkg7

1)

0.63a

0.13b

0.46ab

0.50ab

0.16ab

0.48b

0.18b

1.11a

0.13b

Exch

Na(cmolkg7

1)

0.36a

0.11b

0.26a

0.11bc

0.00c

0.18b

0.36a

0.16b

0.11b

CECpot(cmolkg7

1)

13.85b

20.09a

16.61ab

14.90ab

20.66a

15.68bc

12.18c

20.31ab

20.09a

Fe d

(gkg7

1)

22.5

b50.2

a12.3

bc

16.5

bc

6.5

c14.60c

23.27b

12.60c

50.20a

Fe o

(gkg7

1)

9.0

a7.0

b4.1

c3.5

c1.3

c3.76c

9.47a

4.13c

6.95b

Al d

(gkg7

1)

13.0

a7.2

b2.1

c2.0

c1.22c

2.42c

14.28a

4.37c

7.21b

Al o

(gkg7

1)

27.0

a6.7

b3.7

b2.7

b2.0

b3.15b

30.40a

7.73b

6.75b

SiO

2(g

kg7

1)

498c

428d

599b

690a

263e

65d

499a

240c

428b

Al 2O

3(g

kg7

1)

296a

295a

227b

183c

116d

20c

299a

137b

296a

Fe 2O

3(g

kg71)

127b

199a

105c

107c

33d

11d

125b

71c

200a

Notes:Differentletter

subscripts

onthesameproperties

indicate

differencesare

significant(p5

0.05).n¼number

ofsamples.

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Differences in soil properties according to sites and soil types

PCA and CA revealed groupings or clustering of soils as a function of study site andsoil type (Figures 2 and 3). In terms of PCA, all sites were distinctly dispensed in thetwo principal components (PC1 and PC2). PC1 and PC2 explained 28 and 21%of total variability, respectively (Figure 2a,b). PC1 for all data used in the PCAdifferentiates the parent materials of the soil (Figure 2a). Soils originating fromvolcanic rocks (Ormoc, Baybay) contributed to the positive loading, whereas soilsoriginating from limestone and coralline shale contributed to the negative loadingsin PC1, with the exclusion of a few which overlapped. Typical features of limestonesoils such as elevated soil pH (water), exchangeable Ca and total CaO (pH factor,negative eigenvectors) accounted for the largest negative loadings on PC1, whereasAlo, Feo, Corg, Nt and alkaline-earth metals (noncrystalline oxides, alkaline-earthmetal factors, positive eigenvectors), which characterize Andisols and Inceptisolscontributed to the largest positive loadings in PC1 (Table 3 and Figure 2b). Theresult implied that PC1 was increased by the contribution of organic matter,noncrystalline oxides and alkaline-earth metals, and decreased by the contribution ofthe pH factor. PC2 differentiated soils according to the degree of soil development.The well-developed Ultisols in Baybay contributed to the negative loadings, whereasthe less-developed Andisols, Inceptisols and Alfisols contributed to the positiveloadings. The negative loadings in PC2 were contributed by the crystalline andamorphous Fe oxides and the dominance of resistant oxides, particularly TiO2 andFe2O3 (Figure 2b), implying strongly weathered soils in Baybay (Navarrete et al.2009) and Bato, respectively. In general, the PC1-PC2 plots revealed that changesin the distribution patterns of soils from the right to the (lower) left reflect thedepletion of exchangeable cations, a decline in pH and an upsurge in the abundanceof weathering-resistant oxides. The result suggests that continued weathering ofInceptisols, Alfisols and Andisols will led to the formation of strongly weatheredsoils such as Ultisols of Baybay.

Figure 2. Plots of the first and second principal components (PC) extracted from theprincipal component analysis (PCA) of all selected.

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The HCA results are in conformity with the PCA. CA of the samples clearlyclustered soils according to soil type, implying the importance of soil formationprocesses and the degree of weathering in every site. The first cluster is representedby Inceptisols with characteristic features of elevated soil pH, exchangeable Ca andCaO, whereas Alfisols (high SiO2) represented the second cluster. By contrast, thethird cluster is represented by Ultisols, which have distinct characteristics ofcrystalline Fe oxides and minerals resistant to weathering, whereas the fourth clusterwas typical for Andosols with high noncrystalline Al and Fe oxides, Corg and Nt.PCA and CA were able to differentiate study sites and soil types, and accordinglywould be an important tool in designing suitable management practices of degradedsoils (Table 4).

Fertility status

Matching selected soil properties with published threshold or favorable values/condition for crop growth or crop production (Tisdale et al. 1985; Landon 1991)allows one to recognize potential fertility constraints to the production ofagricultural crops (Asio et al. 2006). The comparison may provide a basis forplanning suitable soil management strategies for crop production in problem soilssuch as those at our study site.

All soils showed distinctive fertility constraints, as reflected by the negative (7)or positive (þ) sign (Table 5). Rooting depth, which refers to the amount of space

Figure 3. Result of hierarchical cluster analysis for all soil properties (Ward’s method,n¼ 60).

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available for plant roots, was high (450 cm) in all soils. However, there werevariations in rooting depth among soils, as affected by the position of the soils inthe landscape (Table 1). For example, the upper slopes had thinner soils, whereasthicker soils were dominant on the lower slopes of Ormoc and Baybay (data notshown). Regardless of the disturbed nature of the soils, in some sites bulk densitywas low (0.50–1.21 g cm73) probably because of human activities such ascultivation. The low bulk density in the soils of Bontoc, Bato and Matalom isevident in the very good granular structure, whereas in the soils of Ormoc andBaybay, it was due in part to isovolumetric weathering of the parent material(Navarrete et al. 2008, 2009). The dominance of noncrystalline components,particularly allophane and imogolite in the soils of Ormoc (Asio 1996; Navarreteet al. 2008) and the abundance of halloysite in the soils of Baybay (Asio 1996;Navarrete et al. 2009), contributed to the low bulk density in these soils. In all soils,low bulk density indicates high porosity and accordingly, excellent gas exchangebetween the roots and atmosphere. The main physical constraint that likelyinfluences soil use and management in Baybay (sites 6, 7 and 9), Bontoc (site 10) and

Table 3. Loadings of the first three principal components with eigenvalue, cummulativepercentage of variation and estimated communalities of the variables.

Variables PC 1 PC 2 PC 3 Communality

pH 70.70 0.50 70.25 0.80Corg 0.66 0.25 70.28 0.58Nt 0.66 0.26 70.32 0.60Exch Ca 70.74 0.46 70.43 0.95Exch Mg 70.01 70.03 0.71 0.51Exch K 0.35 0.23 70.01 0.18Exch Na 0.69 0.22 70.03 0.52CECpot 70.28 70.15 70.07 0.11Fed 70.02 70.91 70.01 0.83Feo 0.72 70.22 70.22 0.61Ald 0.69 70.18 70.39 0.65Alo 0.68 0.18 70.38 0.63Feo/d 0.60 0.47 70.15 0.61SiO2 0.45 0.21 0.74 0.79Al2O3 0.59 70.59 70.08 0.70Fe2O3 0.25 70.92 0.13 0.94MnO 0.82 70.05 70.26 0.74TiO2 0.19 70.89 0.21 0.86CaO 70.71 0.46 70.49 0.96MgO 0.54 0.48 70.24 0.58K2O 0.65 0.58 0.22 0.81Na2O 0.57 0.53 0.27 0.68P2O5 0.64 0.21 70.49 0.68As 0.19 0.48 0.48 0.49Co 0.46 70.38 0.37 0.50Cr 70.22 0.12 0.90 0.87Cu 0.09 70.08 0.24 0.07Ni 70.03 0.55 0.63 0.71Pb 0.27 0.67 0.50 0.77Zn 0.47 70.35 0.26 0.41Eigenvalue 7.34 6.61 5.20 19.14Cummulative % of variation 24 46 64

Note: The major contributions of the original variables on each PC are printed in bold type.

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Table

4.

Selectedsoilproperties

ofthesurface

soillayer

ofallstudiedsites.

Exchangeable

Depth

pH

Corg

Nt

Ca

Mg

KNa

CECpot

Cu

Zn

Location

SiteNo

Horizon

(cm)

(water)

(%)

(cmolkg7

1)

(mgkg71)

Orm

oc

1Ap

0–10

4.8

6.3

0.62

0.79

0.30

0.42

0.34

18.2

58

71

Orm

oc

2Ap

0–16

5.1

4.9

0.45

1.18

0.31

0.20

0.49

14.2

55

49

Orm

oc

3Ap

0–12

5.7

7.3

0.85

4.28

1.83

2.19

0.27

19.0

68

89

Orm

oc

4Ap

0–15

5.0

4.7

0.44

0.27

0.19

0.16

0.34

20.5

52

56

Orm

oc

5Ap

0–8

4.7

5.2

0.53

1.20

0.45

0.29

0.33

19.3

51

54

Baybay

6Ah

0–8

5.1

2.9

0.33

1.28

0.95

0.26

0.05

15.6

54

78

Baybay

7Ah

0–20

5.1

1.7

0.21

1.21

0.66

0.17

0.07

11.1

52

70

Baybay

8Ah

0–10

5.7

2.1

0.24

4.97

2.02

0.19

0.07

33.5

49

88

Baybay

9Ap

0–11

5.2

2.7

0.30

1.01

0.86

0.50

0.02

17.2

63

88

Bontoc

10

Ah

0–11

6.9

4.9

0.36

3.6

1.99

0.61

0.02

16.0

60

86

Bato

11

Ah

0–12

5.1

1.5

0.16

4.9

1.50

0.56

0.03

15.2

43

40

Matalom

12

Ah

0–7

7.8

3.6

0.44

89.3

0.20

0.08

0.00

11.3

60

40

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Table

5.

Fertility

contraints

tocropgrowth

orproductionofdegraded

uplandsoilsbasedonthesurface

layer

ofthesoil.a

Available

Exchangeable

Site

Depth

Bulk

density

pH

Corgf

Ntf

PCaf

Mgg

Kf

Cuh

Znh

Soilproperties

No.

(cm)c

Texture

d(g

cm73)e

Consistence

(water)f

(%)

(mgkg7

1)f

(cmolkg71)

(mgkg71)

Threshold

valueb

450

Medium

51.45

fr,np,ns

5.5–7.0

43.0

40.2

48–15

40.40

40.50

40.20

40

410

Orm

oc

1þ

þþ

þ7

þþ

7þ

7þ

þþ

Orm

oc

2þ

þþ

þ7

þþ

7þ

7þ

þþ

Orm

oc

3þ

þþ

þþ

þþ

7þ

þþ

þþ

Orm

oc

4þ

þþ

þ7

þþ

7þ

77

þþ

Orm

oc

5þ

þþ

þ7

þþ

7þ

þ7

þþ

Baybay

6þ

7þ

77

7þ

7þ

þþ

þþ

Baybay

7þ

7þ

77

7þ

7þ

þ7

þþ

Baybay

8þ

þþ

þþ

7þ

7þ

þ7

þþ

Baybay

9þ

7þ

þ7

7þ

7þ

þþ

þþ

Bontoc

10

þ7

þþ

þþ

þ7

þþ

þþ

þBato

11

þþ

þþ

77

77

þþ

þþ

þMatalom

12

þþ

þþ

7þ

þ7

77

7þ

þ

Note:aExceptfordepth,whichconsiderssolum

thickness.

bItcanalsobecalled

‘favorablevalueorcondition’.

cBasedonSchlichtinget

al.(1995).

dBasedonLandon(1991).

Claytexture

withgranularstructure

isfavorable.eBasedonArshadet

al.(1996).

f BasedonLandon(1991).

gBasedonHabyet

al.(1990).

hBasedonSim

s(1999).fr,friable;np,

nonplastic;ns,nonsticky.

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Bato (site 11) is the heavy clay, which becomes hard when the soil is dry and veryplastic and sticky when the soil is wet. When very plastic and sticky, the soil becomestroublesome for farming due to resistance and compression. However, soils inOrmoc (sites 1–5), Baybay (site 8) and Matalom (site 8) were mostly medium-textured, containing elevated amounts of sand and silt, implying favorableconditions for crop production.

Soil reaction measured in terms of pH influences many soil properties includingCEC, nutrient availability and the aggregation of soil particles (Landon 1991). SoilpH is very useful in the evaluation of fertility because it provides information on thepotential availability or phytotoxicity of plant nutrients and nonessential elements inthe soil (Landon 1991; Sims 1999). The water pH in the soils of Ormoc (site 3),Baybay (site 8) and Bontoc (site 10) were within the favorable limits (5.5–7.0) forcrop growth (Landon 1991). The alkaline and acid pH are constraints for cropgrowth in site 12 and sites 4, 5, 6, 7, 9 and 11, respectively. Sims (1999) explainedthat, in alkaline conditions, the availability of plant nutrients is reduced because ofthe decreased solubility of P, Cu, Fe, Mn and Zn or greater sorption of B, whereas inacidic conditions, the plant availability of Ca, Mg, Mo and P is decreased because ofthe increased solubility of Al and Mn, resulting in plant toxicity of Al. The largedeviation in pH among the soils implies a distinctive fertility status, inasmuch as thesolubility of micronutrients and various nonessential trace elements is highly pHdependent. In terms of soil fertility management, the large deviation in pH impliesdifferent fertility management among the different soils. The Corg content was high inthe soils of Ormoc (average: 3.02%) and low in the soils of Baybay (average: 1.27%),Bato (average: 1.07%) and Matalom (average: 1.07%). The high Corg content in theAndosols of Ormoc may be due to the formation of organo-mineral compounds thatrestrain organic matter decomposition (Shoji et al. 1993), whereas the low Corg

content in the soils of Baybay, Bato and Matalom may be due to past land use andvarious human activities. Nitrogen turnover in tropical soils is elevated by hightemperature and moisture (Jahn 1999), and accordingly the availability of N is nota limiting factor in the soils in this study, except for site 11 of Matalom. In all soilsthe availability of P (53 mg kg71) was notably below the suitable amounts of 8–15mg kg71 (Landon 1991), suggesting that P is the main restricting nutrient in thesedegraded soils (Siebert 1987; Asio 1996; Navarrete et al. 2007; Navarrete andTsutsuki 2008). The low P availability in the soil can be explained by the low Pcontent of the parent material, by the alkaline or acidic chemical condition of thesoils and in volcanic soils, particularly Andisols in Ormoc, to the reaction of P withnoncrystalline Al and Fe oxides, resulting in the formation of insoluble metal-Pcompounds (Shoji et al. 1993). The capability of native vegetation to succeed in lowP availability, particularly in Baybay (sites 6, 7 and 8) may be due in part to anexternal input of P into the forest ecosystem (Zikeli et al. 2000; Sueta et al. 2007) andto mycorrhizal association (Jordan 1985).

In terms of nutrient availability, exchangeable Ca was adequate (40.40 cmolkg71) in all soils, except those of Matalom, which have a very high exchangeable Cadue to the limestone parent material. In accordance with Tisdale et al. (1985), excessCa, as in the case of Matalom soils, is a constraint because as the Ca/Mg ratioexceeds 7:1, Mg becomes deficient. Sites 1, 2, 4 and 12 exhibited constraint due toexchangeable Mg, as reflected by its low amount in the soils, whereas exchangeableK was not limiting in sites 1, 2, 3, 6, 9 and 11. Cu and Zn levels were suitable for cropgrowth, as reflected by their high levels in the soil. Although it was not observed in

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the calcareous soil of Matalom, Tisdale et al. (1985) stated that Zn is deficient incalcareous soil because it is adsorbed on carbonates.

Conclusion

Our findings showed that most of the soil physical and chemical constraints aredirectly or indirectly related to the nature and qualities of the parent material,geomorphic position and anthropogenic effects, such as land use. In addition, thesoil fertility characteristics assessed here have distinctive dynamics even withinsimilar soil types, primarily due to their distinct relationship with the dominant soil-forming processes. Careful consideration of the physical and chemical constraintsare essential in planning long-term soil management strategies that will lead to thesustainable utilization of these problem soils.

Acknowledgement

The first author is grateful to the Ministry of Education, Science, Sports and Culture of Japanfor the scholarship support.

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