Chapter 2

Beyond the Horizons: Challenges and Prospects for Soil Science and Soil Care in Southeast Asia

Karl Stahr, Gerhard Clemens, Ulrich Schuler, Petra Erbe, Volker Haering, Nguyen Dinh Cong, Michael Bock, Vu Dinh Tuan, Heinrich Hagel, Bui Le Vinh, Wanida Rangubpit, Adichat Surinkum, Jan Willer, Joachim Ingwersen, Mehdi Zarei, and Ludger Herrmann

Abbreviations

CEC Cation exchange capacity

CV Coefficient of variation

K. Stahr (*) • G. Clemens • P. Erbe • V. Haering • M. Zarei • L. Herrmann Department of Soil Science and Petrography (310a), University of Hohenheim, Stuttgart, Germany

e-mail: Karl.Stahr@uni-hohenheim.de

U. Schuler

Department of Soil Science and Petrography (310a), University of Hohenheim, Stuttgart, Germany

Federal Institute of Geosciences and Natural Resources (BGR), Hanover, Germany

N.D. Cong • B. Le Vinh

Department of Soil Science and Petrography (310a), University of Hohenheim, Stuttgart, Germany

Faculty of Natural Resources and Environment, Hanoi University of Agriculture, Hanoi, Vietnam

M. Bock • J. Willer

Federal Institute of Geosciences and Natural Resources (BGR), Hanover, Germany

V.D. Tuan

Department of Plant Production in the Tropics and Subtropics (380b), University of Hohenheim,

Stuttgart, Germany

H. Hagel

Department of Computer Applications and Business Management in Agriculture (410c),

Hohenheim University, Stuttgart, Germany

W. Rangubpit • A. Surinkum

Department of Mineral Resources (DMR), Bangkok, Thailand

J. Ingwersen

Department of Biogeophysics (310d), University of Hohenheim, Stuttgart, Germany

H.L. Fröhlich et al. (eds.), Sustainable Land Use and Rural Development in Southeast Asia: Innovations and Policies for Mountainous Areas, Springer Environmental Science and Engineering, DOI 10.1007/978-3-642-33377-4_2, # The Author(s) 2013

31

mailto:Karl.Stahr@uni-hohenheim.de

DEM Digital Elevation Model

DMR Department of Mineral Resources Bangkok

FAO Food and Agriculture Organization of the United Nations

K Potassium

m.a.s.l. Meter above sea level

OOB Out Of Bag

PCA Principal Component Analysis

PRA Participatory Rural Appraisal

RSG Reference Soil Group

SEA Southeast Asia

eTh Thorium equivalent

Th Thorium

eU Uranium equivalent

U Uranium

WRB World Reference Base for Soil Resources

2.1 The Need for Sound Soil Information in Mountainous Tropical Areas1

The quality and quantity of information on soils in the mountainous areas of

Southeast Asia (SEA) is still poor; therefore, the aim of soil research work must

be twofold: (1) to gain information about soils, in order to facilitate interdisciplin-

ary research, and (2) to proactively improve soil analysis and soil monitoring

methods in order to try out new methods, those not yet applied in a given area.

To meet the first aim, our research developed a soil map for north-west Thailand at

a scale of 1:200,000 and specific soil maps for other key areas in SEA. With the

same aim, research into soil development in the limestone areas of SEA helped

improve soil knowledge, because soils and limestone are not found to a large extent

in other savannah regions of the world. Finally, in Vietnam, research was carried

out into the impacts of soil erosion on soil fertility, again with the first aim in mind.

For the second aim, methodological progress has been achieved through the use of

non-destructive gamma ray spectrometry, a method which can be used multiple

times and across spatial scales. Mapping has also been carried out in a number of

local areas in order to compare traditional ground-check methods with local

knowledge, statistical methods and digital soil mapping. The first aim is mainly

dedicated to the improvement of soil knowledge and to help with land use planning

in the uplands of SEA, while the second aim is focused on developing methods for

use in research across other areas.

1 This section was written by Karl Stahr with Ludger Herrmann, Ulrich Schuler and Gerhard

Clemens.

32 K. Stahr et al.

The highlands of northern Thailand have changed over the last few decades, due

to population growth, changing political paradigms and economic development

(see Chap. 1). A soil database is crucial for sound land use planning, but is currently

lacking in the highlands of northern Thailand; therefore, one objective of the soil

sciences element of the Uplands Program was to establish a regional soil map based

on stepwise up-scaling and using innovative mapping approaches. Gamma-ray

spectrometry has proved to be a useful tool for soil mapping on all scales, given a

sound process understanding to infer the detected signals. Section 2.2 introduces the

principles of gamma-ray spectrometry, explains its use for soil mapping, and

presents its application at the soil profile and landscape scale.

The soil resources of northern Thailand play an important role in the mostly

agrarian-based livelihoods of the local populations there; hence, site-adapted

land management strategies are necessary that require detailed soil information.

As comprehensive and intensive soil mapping activities are not affordable,

alternative mapping approaches need to be utilized. Several soil mapping

approaches on a meso-scale (>1:100,000 scale) have been developed, namely the catena-based, grid-based randomized and indigenous knowledge approaches

(see Sect. 2.3). Comparisons of these approaches in northern Thailand have

shown that the catena approach is accurate, but labor intensive and time con-

suming. The grid-based randomized mapping approach is fairly accurate; how-

ever, it is quite difficult to locate the predefined sampling points in steep terrain

and with high vegetation density. The local knowledge approach is quite accu-

rate and rapid, yet restricted to the village level and its ethnic context, meaning

the results are thus not transferable across sites, with mapping criteria based on

local experiences. An alternative is scale-independent soil prediction approaches

based on statistics and the use of airborne gamma–ray data. These comprise inter alia the application of (a) maximum likelihood, (b) classification trees, (c) and random forest algorithms. Comparing these approaches when used in northern

Thailand, the random forest approach performed the best (Sect. 2.3),

demonstrating the feasibility of producing meso-scale soil maps for almost the

whole of Thailand using airborne radiometric data sets.

The search for measures and policies to mitigate the negative effects of land use

intensification in mountainous areas of SEA is based mostly on simple economic

indicators, which do not account for an efficient and comprehensive analysis of the

natural and socio-economic context, and so often neglect the needs and interests of

local people. They also do not integrate indigenous knowledge. Spatial information

needed for the qualitative and quantitative evaluation of soil and land resources, a

prerequisite for the development of sustainable resource management, is poor and/

or not available on the necessary scale. The question therefore arises as to whether

local soil knowledge can help to overcome this shortcoming. The case study detailed

in Sects. 2.3 and 2.4 investigated the potential for local soil knowledge to help

gather spatial soil information across various parts of SEA and various ethnic

groups, using Participatory Rural Appraisal (PRA) tools, then compared this with

soil information obtained using conventional scientific methods. Despite its geo-

graphical restriction, the identification of local soil knowledge through PRA can be

2 Beyond the Horizons: Challenges and Prospects for Soil Science and Soil. . . 33

http://dx.doi.org/10.1007/978-3-642-33377-4_1

used (1) to optimize conventional soil mapping by minimizing the required number

of samples, (2) for soil suitability assessments and (3) is as such a key to sustainable

land use planning on the local scale, as it facilitates the participation of local people

in the decision making process.

While limestone areas are relatively rare in the tropics, they are extensive in

SEA and their characterization play an important role for land use planning.

Therefore, research into Paleozoic and Mesozoic limestone soils in the northern

parts of Thailand, Laos and Vietnam was carried out (see Sect. 2.5), with the

dominant soils found being Alisols and Acrisols in Thailand, Acrisols associated

with some Luvisols in Laos and Luvisols associated with Alisols in Vietnam.

Clay minerals showed a sequence running from illite through vermiculite to

kaolinite. Gibbsite was abundant in Thailand, where limestone showed intrusions

of iron ore, while goethite and hematite were also found. Kaolinite- and gibbsite-

dominated soils showed a limited chemical fertility, and most mineral nutrients

were restricted to the relatively fertile topsoil layer. These differences were due to

the different stages of soil development and young soil/sediment translocations.

In princi