Statistical and hydrological modeling of soil and subsoil salt-accumulation caused by tree
plantations established above shallow saline groundwater
Introduction
In Hungary there was a great increase in the acreage of afforested areas during the last hundred
years, from 1.1 to 1.8 million ha. Most of these are plantations were established on previous
grassland/cropland, ca 60%. European Union incentives favor further afforestations, and there are
ca 15 000 hectares being afforested on earlier croplands each year. For the coming 30 years some
700 000 ha more afforestation is planned (Andrasevits et al., 2005). Although it has been
demonstrated that trees cause subsurface salt accumulation above shallow saline groundwater in
areas with negative water balance (Bazykina 2000, Nosetto et al., 2007, 2008), when the decision
on afforestation of a particular plot is made there is no allowance made for the salinity of
groundwater, therefore a future risk is incorporated in every such case.
The area suggested for afforestation by the National Forest Strategy, 2009 covers areas where
other agricultural activity is not profitable, and this area is overlapping with the area of saline
shallow groundwaters as shown by Map 1. and there is a considerable risk that undesired,
deleterious salt accumulation will occur in newly afforested areas.
Map 1. Total soluble salt concentration of groundwater in the Great Hungarian Plain
The model of the study
The hydrological effect of trees is much different from the crops or grasses, being characteristic
for the earlier land-use. Due to their deep roots, trees extract water from much deeper layers and
there is an increased water absorption and transpiration. As Fig 1 from Jobbágy et Jackson, 2004
shows there is a tendency of salt accumulation under the established tree stand. Where the
conditions are favorable a horizontal groundwater flux will accelerate the rate of salt
accumulation.
Figure 1. The scheme of salt accumulation above a shallow groundwater as described by Jobbágy
and Jackson, 2004
With our project our intention is to quantify the risk and provide guidelines for the optimal
selection of plots and trees in order to reduce the risk of subsurface salt accumulation in
Argentine and Hungary with the same methodology and evaluation techniques. The model of the
study is shown in Fig 2 of Nosetto et al., 2008. Here we list those factors that affect the
underground salt accumulation under tree stands, and which are studied in the project one-by-one.
The positive factors on the left of the figure increase the chance of salt accumulation. The project
aims at describing the complex interrelation of the listed factors in such a way that the effect of
new afforestations could be predicted.
Objectives
The objective of the suggested studies is the detailed investigation of the Hungarian situation
through the systematic study of the affecting factors and to give suggestions for the prevention of
expected problems. There will be two scales as hinted by Fig 2. At the regional scale throughout
the Great Hungarian Plain altogether 243 afforested plots will be visited to collect data on
groundwater, soil and vegetation characteristics. These data will be used in a statistical modeling
for the prediction of the effect of afforestation on soil, subsoil, groundwater characteristics. At the
stand-scale studies carried out at 16 selected plots the effect of age group of trees, groundwater
level, groundwater salinity and soil texture on the transpiration of trees will be assessed by
detailed temporal monitoring.
The suggested research is fundamental research, because the main objective is to find a predictive
model of expected salt accumulation. This a novel research because of the comprehensive
consideration of all important factors of salt accumulation. Only limited number of factors were
studied so far by Nosetto 2007, 2008, Bazykina, 2000 and others, and the spatial variability of
soil texture is disregarded. In Hungary it is a very strong limiting factor and deserves
consideration as suggested by Várallyay, 2002.
Factors studied
All the modifying factors listed in Fig 2 will be studied in the project. In our previous paper the
effect of climatic water balance was described in detail for the Argentine Pampas. Throughout the
Great Hungarian Plain there is a great range found in the annual climatic water deficit (difference
between potential evaporation and precipitation), ranging from 100 to more than 250 mm (Pécsi
et al., 1985) as shown by Fig 3, but the effect of these differences on soil or subsoil salt
accumulation have not been evaluated yet.
Fig 3. The annual climatic water deficit in Hungary
The range of groundwater depths (watertable) in the Great Hungarian Plain (GHP) was tabulated
by Tóth et al., 2001 and ca 77% of the area was found to lie above groundwater depths between 1
and 4 meter. The same publication showed that in ca 59% of the GHP areas have shallow
groundwaters more saline than 1 g/l. Also Tóth et al. (2001) listed the typical subsoil textural
sequences in GHP and found that 45% of the area can be characterized as clay, 12% as sand
down to the depth of 10 m. Some 30% of the area are characterized by variable layers of silt, sand
and clay.
At present the most common tree species used for afforestation in the GHP are English oak,
(Quercus robur L.), black locust, (Robinia pseudoacacia L.) and various poplars, most often
(Populus alba L., P. ×canadensis Moench). These trees are characterized by different growth rate,
rooting system and rooting depth according to Crow, 2005. The order of salt tolerance between
the species is hypothesised to be Q robur > P species > R pseudoacacia but all three species have
some tolerance according to UMES, 2004.
A further factor affecting the salt accumulation is the stand age. This factor determines rooting
depth, growth rate and related water uptake and results in increasing salt accumulation
underground by time (Bazykina,2000).
Methods used in the project
During three years of field data collection 243 afforested plots will be visited and there
groundwater, subsoil, soil and tree growth parameters will be collected. The studied 243 plots
will represent the most important combinations of the factors which affect the subsoil salt
accumulation as shown in Fig 2. The number of study sites is received as 35 based on the
following combinations: three mentioned species [Q robur, R pseudoacacia, P species] X
common texture sequences [clayey, sandy, variable silty] X common groundwater depth [1-2, 24, 4-8 m] X groundwater salinity [1-2, 2-5, 5-10 g/l] X stand age [10-20, 30-40, 50-60 year].
There will be two versions of the equations: one numerical based on the measured data and one
using categories of widely available information sources, such as AGROTOPO database
(Várallyay and Molnár, 1989), existing groundwater depth and salinity maps by Tóth et al., 2001.
At each plot four boreholes will be made (two inside, two outside of the plot in order to provide
replicates) in a transect delineated based on the heterogeneous growth of vegetation.
The effect of existing soil and subsoil salinity on the tree growth characteristics will be analysed
in those studied plots, which are covered by a series of available ASTER satellite images (Fig 4.)
with spring and autumn recordings.
The novelty of this study plan is the vertical and horizontal integration of three different
approaches plus the parallel Argentine studies. This way the undisclosed constants and regression
coefficients in the equations formulated for the regional scale can be explained based on
hydrological measurements carried out at stand scale. The final evaluation of the two databases
will be carried out together by the two national teams. The databases of the two national groups
will have the same structure and each element of study at both spatial scales will be compatible.
Fig 4. The cover of available ASTER satellite images
Expected results
The results of the study will show the effect of contrasting vegetation types on salt accumulation.
Not evident interactions between tree salt tolerance, soil and subsoil texture sequences and
groundwater depth and salinity will be described by the numerical equations between salt
accumulation and affecting factors. The results will give very clear answer to the long-time
speculated effect of afforestations on groundwater depth in the Great Hungarian Plain. The extent
of progressive salt accumulation under older stands will help to evaluate the phenomenon of tree
dieback, being characteristic in salt-affected regions. The data collected on the temporal
fluctuation of groundwater will give a very important physiological indicator and will help the
future selection of promising tree genotypes for the GHP. With the data collected an open
database will be created about areas lying above shallow groundwater. The scientific importance
of the database is manifold: it provides a basis for the analysis of land use effects on basic soil
and subsoil parameters, first of all salt accumulation. Besides it will contain basic biometric data
on the tree stand and groundwater depth, which are basic for environmental monitoring. This way
the project will provide useful, often highly demanded data for spatial and temporal monitoring
both on soils and subsoils, adding new data to the database of Research Institute for Soil Science
and Agricultural Chemistry of the Hungarian Academy of Sciences (RISSAC-TAKI) and
Hungarian State Geological Institute (HSGI-MÁFI) as well.
The practical importance of the results is straightforward, because with the use of the equations
describing salt accumulation (dependent variable) with the categories of affecting factors
collected from easily available databases (independent variable) the planning of new
afforestations is greatly facilitated, and this way the undesirable process of salt accumulation in
soils and subsoils will be prevented.
Preliminary Research
The basic series of the geology of the GHP was developed by Hungarian State Geological
Institute in the seventies-eighties of the last century by the participation of László Kuti. He,
together with RISSAC staff members has assessed the hydrogeological factors of soil salinization
in Tóth et al., 2001. The current tendencies of soil salt concentratin in relation with the
groundwater level have been described by Tóth et al., 2006.
During the preceding years the collaboration with the Argentine team resulted in two papers on
the situation in a few oak stands inside Hungary, which is described in Nosetto et al., 2007 and
another on the regional situation in Argentina in Nosetto et al., 2008. These were the bases of one
PhD thesis and several other publications.
The competence of the RISSAC team in the use of field techniques for the characterization of soil
salt accumulation with geoelectric instruments was shown by the publications Douaik et al., 2007,
Tóth et al., 2006. The suggested augering techniqe was used by Tóth and Várallyay, 2001 for the
description of the relationship of soil and subsoil salt accumulation with groundwater depth and
salinity.
Workplan
1st year:




Development of the joint stand preselection methodology, database structure,
instrumentation and field protocol for the project by the two national teams.
Selection of the studied afforested plots based on the combination of affecting factors as
presented in publications of Tóth et al., 2001, the series of Geological Atlas of Hungary
and the register of forests at the National Forest Authority. Each site and the
corresponding boreholes and transects will be selected with the visual aid of generally
available satellite and aerial records of Google Earth and MEPAR (Hungarian
Agricultural Plot Identification System).
From the 243 plots selected for regional-scale study 16 will be selected for stand-scale
study based representativity.
Already during first year and each following year the local data collection of groundwater
changes together with accompanying soil salinity, moisture and temperature plus weather
data will be collected at one fourth of the plots selected for it during more than six
months preceding leaf fall. The reason for salinity and moisture monitoring is the need to
study the effect of changing salinity on transpiration. Based on the temporal monitoring
of detailed groundwater level fluctuations and the chemical composition of groundwater
and soil and subsoil layers and other affecting factors the transpiration of the stands will
be estimated and compared to estimates received on the basis of chloride balance
calculations.
2nd year:
 Regional-scale data collection at one third of the plots during September and October. At
each selected plot the elevation above sea level will be determined for the boreholes.
There will be two boreholes outside the studied plot in grassland/cropland on two
opposite sides of the afforested plot at distances not shorter than 50 m from the edge of
the afforested plot. There will be two boreholes inside the plot at distances not shorter
than 50 m from the edge and each other. Along the transects, the bulk electrical
conductivity of the soil will be measured with an electromagnetic induction probe and
calibration samples will be collected. From the boreholes the texture sequence will be
determined by field geological assessment. Also from the each 20 cm layer laboratory
texture analysis will be performed for sand, silt and clay fractions. From the same layers
soil salinity, alkalinity and sodicity and chloride content will be determined. The depth of
groundwater found and risen after 30 minutes will be determined. A groundwater sample
will be collected and analysed in the laboratory for electrical conductivity, Na, Cl,
carbonates and bicarbonates. Along the transect the tree trunk circumference, tree height
will be determined in order to estimate the timber volume. In the transect segments
outside the tree stand the biomass will be measured by cutting the aboveground plant
mass and subsequent drying.
 Continuation of stand-scale data collection at another fourth of the plots selected for this
research.
 Biomass estimation of plots covered by the satellite image limits will be carried out by
the ASTER satellite images.
3rd year:



Continuation of regional-scale data collection at another third of the plots.
Continuation of stand-scale data collection at another fourth of the plots selected for this
research.
Biomass estimation of plots covered by the ASTER satellite images.
4th year:





Continuation of regional-scale data collection at another third of the plots.
Continuation of stand-scale data collection at another fourth of the plots selected for this
research.
Biomass estimation of plots covered by the ASTER satellite images.
Statistical analyses of data will be carried out for the collected data.
At regional scale for each tree species the salt accumulation of stands versus nearby
grasslands/croplands will be predicted by the studied independent variables shown by Fig
2, climatic water balance, clay percent, groundwater salinity, groundwater depth, stand
age. The correlation between timber volume and soil salt accumulation will be studied at
this regional scale also inside the area covered by ASTER satellite images the tree
biomass will be estimated by Normalized Differential Vegetation Index and its
correlation with soil and subsoil salt accumulation will be calculated. At stand scale the
analysis of groundwater fluctuations and the chloride curves of underground layers will
provide two independent estimates of tree transpiration as described by Nosetto et al.,
2007.
Work flow between Hungarian partners, covering the personal responsabilities











Selection of study sites
Preparation of basic hydrogeological spatial database on the combinations of
hydrogeological factors: L Kuti
Selection of relevant afforestations: I Csiha and Z Gribovszki
Interpretation of salt tolerance of species: I Csiha
Field geological augering and description: L Kuti
Field characterization of stands: A Szabó
Field installation of groundwater monitoring stations: Z Gribovszki
Sample analysis: A Szabó
Statistical modeling: T Tóth
Hydrological modeling: Z Gribovszki
Remote sensing analysis: A Szabó
History of collaboration between the Hungarian and Argentine teams
The two teams collaborated in a Hungarian-Argentine Intergovernmental project 2004-2005
“Vegetation and salt/water dynamics in flat landscapes: Comparative and
complementary studies in Pampa Deprimida”. The principal investigators of the project were
Tibor Tóth from the Hungarian side and Esteban Jobbágy from the Argentine side. The results of
the collaboration are published in the papers Nosetto et al., 2007 on the salt accumulation in a
Hungarian study site and in Nosetto, 2008 on the analysis of the situation in the Pampa
Deprimida, and also his PhD thesis: “Conversion of grasslands into forests: the impact on the
water and salt dynamics. Universidad de Buenos Aires, 2007.
Most important interactions between Argentine and Hungarian research groups during the
project








Collaboration in the study site selection and parallel instrumentation at mutual level
Joint development of the structure of field database and field protocol.
Supervision of site selection at mutual level.
Supervision of soil property selection and analytical methods by Hungarian team.
Supervision of remote sensing analysis by Argentine team.
Supervision of hydrological instrumentation by Hungarian team.
Supervision of ecohydrological interpretation by Argentine team.
Supervision of statistical interpretation by Hungarian team.
Required infrastructure



The maps required were developed by the Research Institute for Soil Science and
Agricultural Chemistry of the Hungarian Academy of Sciences and Hungarian State
Geological Institute and are available. The location of possible afforested stands will be
determined based on the advise given and database accessed by the Station for
Afforestation of Salt-Affected Areas of the Forestry Research Institute.
The augerings will be carried out by the staff of Hungarian State Geological Institute.
The field devices necessary for the field bulk electrical conductivity measurements
(EM38 2K, EMRC-120) are available in RISSAC.






The devices necessary for temporal monitoring of groundwater depth and meteorological
elements will be purchased with the contribution of the project funding.
The devices used for timber volume estimation are available at the Station for
Afforestation of Salt-Affected Areas of the Forestry Research Institute.
The GIS software ArcView is available at RISSAC. The ASTER satellite images are
available at RISSAC together with the ERDAS processing software.
The necessary desktop computers, GPS and leveling instruments are available at
RISSAC.
A field notebook will be purchased with the funds provided by the project.
A four-wheel vehicle for access and transport is available at RISSAC.
Personnel of the project
At RISSAC the following personnel is available for the project
 Tibor Tóth principal investigator
 András Szabó PhD student
 Newly employed PhD student will be payed with project funding.
At the Hungarian State Geological Institute the following personnel is available for the project
 László Kuti, head of the Department of Environmental Geology
At the Station for Afforestation of Salt-Affected Areas of the Forestry Research Institute the
following personnel is available
 Imre Csiha, station director
At the University of Western Hungary the following personnel is available
 Zoltán Gribovszki, associate professor
References:
Andrasevits, Z., Buzás, Gy., Schiberna E. 2005. Current afforestation practice and expected
trends on family farms in West Hungary. Journal of Central European Agriculture. 5:297-302.
http://www.agr.hr/jcea/issues/jcea5-4/pdf/jcea54-8.pdf
Bazykina, G. S. 2000. Ecological Assessment of Meadow-Chestnut Soils
of the Solonetzic Complex Ameliorated by Means of Afforestation
in Nonirrigated Conditions in the Northern Caspian Region. Pochvovedenie. No.11. 1340-1348.
Crow, P. 2005. The influence of soils and species on tree rooting depth. Forestry Commission
Information Note. November 2005
www.forestry.gov.uk/pdf/fcin078.pdf/$file/fcin078.pdf
Douaik, A., M. Van Meirvenne, T. Tóth . (2007.) Statistical methods for evaluating soil salinity
spatial and temporal variability. Soil Science Society of America Journal. 71:1629-1635.
http://www.taki.iif.hu/english/soilsci/toth/abstr/235DMT2007FULL.pdf
National Forest Strategy, accessed 2009.Ministry of Agriculture and Regional Development.
www.fvm.hu/main.php?folderID=2336
Nosetto, M D., E. G. Jobbágy, T Tóth and C. M. Di Bella (2007.) The effects of tree
establishment on water and salt dynamics in naturally salt-affected grasslands. Oecologia. 152:
695-705.
http://www.taki.iif.hu/english/soilsci/toth/abstr/230NJTB2007FULL.pdf
Nosetto M.D., Jobbágy M. G., Tóth T., Jackson R. B. (2008.) Regional patterns and controls of
ecosystem salinization with grassland afforestation along a rainfall gradient. Global
Biogeochemival Cycles. 22 doi:10.1029/2007GB003000
http://www.taki.iif.hu/english/soilsci/toth/abstr/NJTJ2008.pdf
Pécsi, M. 1985. National Atlas of Hungary.Kartográfia. Budapest.
Tóth T., Kovács, D., Marth, P., 2006 Mesoregional variability of the salt content of the genetic
horizons of salt-affected soils as shown by the Hungarian Soil Monitoring System. 2006
Talajvédelem Különszám Talajtani vándorgyűlés Sopron, pp 192-201. (in Hungarian)
Tóth, T., and L. Kuti. (1999.) Geological factors affecting the salinization of the Nyirolapos
Sample Area (Hortobagy, Hungary). I. General geological characterization, calcite concentration
and pH values of subsurface layers. (in Hungarian). Agrokémia és Talajtan. 48: 431-444.
http://www.taki.iif.hu/english/soilsci/toth/abstr/TK99FULL_5-6.PDF
Tóth, T., and Gy. Várallyay (2001.) Variability of soil conditions in relationship with salinization.
(in Hungarian). Agrokémia és Talajtan. 50:19-34.
http://www.taki.iif.hu/english/soilsci/toth/abstr/TV2001FULL.pdf
Tóth, T., L. Kuti, S. Kabos, and L. Pasztor L. (2001.) Use of digitalized hydrogeological maps for
evaluation of salt-affected soils of large areas. Arid Land Research and Management. 15: 329346.
http://www.taki.iif.hu/english/soilsci/toth/abstr/TKKP2001FULL.pdf
Tóth T., L. Kuti, and U. Fügedi (2003.) Monthly studies at Zab-szék saline lake. Temporal
changes of lake water, groundwater, soil and vegetation. (in Hungarian) Természetvédelmi
Közlemények. 10:191-206.
http://www.taki.iif.hu/english/soilsci/toth/abstr/TKF2003FULL.pdf
Tóth, T., A. Ristolainen, V. Nagy, D. Kovács, and Cs. Farkas. (2006.) Measurement of soil
electrical properties for the characterization of the conditions of food chain element transport in
soils. Part II. Classification of management units. Cereal Research Communications. 34: (No.1)
163-166. http://www.taki.iif.hu/english/soilsci/toth/abstr/TRNKF2006FULL.pdf
UMES (University of Minnesota Extension Service). 2004. "Protecting Trees & Shrubs
Against Winter Damage", Advocate, Winter 2004
http://on-line-seminars.com/pb/wp_3a6c2c92.html
Várallyay Gy., Molnár E., (1989). The agro-topographical map of Hungary (1:100,000 scale).
Hungarian Cartographical Studies. 14th World Conference of ICA-ACI, Budapest: pp. 221-225.
Várallyay, Gy. 2002. Environmental stresses induced by salinity/alkalinity in the Carpathian
Basin (Central Europe). Agrokémia és Talajtan. 51:233-242.