Soil distribution and soil properties in the subalpine region of Kazbegi; Greater Caucasus; Georgia: Soil quality rating of agricultural soils

Accepted Manuscript Soil distribution and soil properties in the subalpine region of Kazbegi; greater Caucasus; Georgia: Soil quality rating of agricultural soils Thomas Hanauer, Carolin Pohlenz, Besik Kalandadze, Tengiz Urushadze, Peter Felix-Henningsen PII:

S1512-1887(16)30073-2

DOI:

10.1016/j.aasci.2016.12.001

Reference:

AASCI 76

To appear in:

Annals of Agrarian Sciences

Received Date: 5 October 2016 Revised Date:

6 December 2016

Accepted Date: 16 December 2016

Please cite this article as: T. Hanauer, C. Pohlenz, B. Kalandadze, T. Urushadze, P. Felix-Henningsen, Soil distribution and soil properties in the subalpine region of Kazbegi; greater Caucasus; Georgia: Soil quality rating of agricultural soils, Annals of Agrarian Sciences (2017), doi: 10.1016/j.aasci.2016.12.001. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT 1

Soil quality assessment

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SOIL DISTRIBUTION AND SOIL PROPERTIES IN THE SUBALPINE REGION

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OF KAZBEGI; GREATER CAUCASUS; GEORGIA: SOIL QUALITY RATING

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OF AGRICULTURAL SOILS

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5 Surnames, first names and patronymics of the authors.

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Hanauer, Thomas*; Pohlenz, Carolin*; Kalandadze, Besik**; Urushadze, Tengiz***; Felix-Henningsen, Peter**

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Name of the institution, address, positions and scientific degrees of the authors.

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*Justus Liebig University Giessen, Institute of Soil Science and Soil Conservation

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Heinrich-Buff-Ring 26-32, Giessen, 35392, Germany; [email protected]: M.Sc. / Dr. /

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Prof. Dr.

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**Ivane Javakhishvili Tbilisi State University, Department of Geography

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1, Chavchavadze ave., Tbilisi, 0179, Georgia; [email protected]: Prof. Dr.

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***Mikheil Sabashvili Institute of Soil Science, Agrochemistry and Melioration, Agricultural University of

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Georgia, 13 km, David Agmashenebeli Ave., 0159, Tbilisi; [email protected]: Prof. Dr.

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ACCEPTED MANUSCRIPT 1

Soil quality assessment

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SOIL DISTRIBUTION AND SOIL PROPERTIES IN THE SUBALPINE REGION

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OF KAZBEGI; GREATER CAUCASUS; GEORGIA: SOIL QUALITY RATING

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OF AGRICULTURAL SOILS

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Keywords: Muencheberg Soil Quality Rating; Alpine Soils; Cambisols (Humic); Cambic Umbrisols; Kazbegi

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ABSTRACT

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Soils of the alpine ecosystem of Kazbegi region were investigated according to the Muencheberg Soil Quality

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Rating (M-SQR). Most limiting factors are climate as well as steepness, while the low nutrient supply and soil

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acidity can be tackled by adequate fertilization and liming practice. Inorganic or organic pollutions were not

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detected. Soils on sediment fans as well as glacial sediments, mostly Cambisols (Humic), are characterized by a

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low to moderate yield potential while high-yield soils, mostly Cambic Umbrisols, can be found on volcanic

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plateaus. A common element of all soils is the high humus content. Actually, most of them are used only for

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pasture, due to poor accessibility. Soils on fluvial deposits, mostly Fluvisols, show a very high range of M-SQR-

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scores. Altogether, the soils of the study area have the actually untapped potential to optimize the basic supply of

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the local population as well as tourism also by cultivation of cereals. Nevertheless, variety trials on different soil

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forming substrates as well as erosion control are major preconditions for successful implementation of new

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cropping systems in the Kazbegi region. Furthermore, particularly rare soils, e.g. Cambisols on Tephra, should

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be protected.

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1.

INTRODUCTION

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Soil quality is, beside climate, the fundamental requirement for prosperity and development of a rural

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population. Therefore, assessment of soil quality, yield potential and soil ecological functions are essential parts

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of the interdisciplinary AMIES II‐project, which aims to support the rural development of the Kazbegi district in

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the Greater Caucasus. It focuses on the human‐environment interface and comprises ecological and socio‐

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economic research to develop sustainable, agricultural land‐use options.

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Due to the Soil Science Society of America (SSSA) soil quality is defined as: ‘the capacity of a specific kind of

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soil to function, within natural or managed ecosystem boundaries, to sustain plant and animal productivity,

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maintain or enhance water and air quality, and support human health and habitation’ [1]. In the frame of the

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project the Muencheberg Soil Quality Rating (M-SQR) for crop and farmland as well as grassland designed by

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[2], valid for a wide range of soils, was applied in the mountainous area of Kazbegi to evaluate the potential of

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agricultural soils of the area on an international basis. The M-SQR was chosen for this purpose, due to its

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concept to ‘measure long-term soil quality and estimate of the local crop potential’, its suitability for grassland as

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well as arable land and especially due to its internationality, because of using the FAO Guidelines for soil

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description [2]. This article summarizes the results of field campaigns in 2014 and 2015.

2.

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STATE OF KNOWLEDGE

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Due to increasing pressure on existing and potential agricultural land a multitude of approaches exist to quantify

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agricultural soil quality resp. the production function. However, due to differing input data ratings are not

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transferable or universally applicable [3]. Soil rating focuses on the evaluation of soil fertility, e.g. yield potential

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of arable soils [4]. Due to Müller et al. [27] three natural limits to growth can be distinguished (1) temperature

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and moisture regime of the soil, (2) internal soil deficits, e.g. a substrate hindering root growth and nutrition

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supply, and (3) the relief. A brief summary of the different approaches has to start with the Californian Storie-

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Index Rating (SIR), evaluating soil type, texture and further parameters (nutrients, erosion etc.) and developed

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already in 1933. It is a multiplicative and parametric System, multiplying percentage performance levels (x:100)

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to get the final so called Storie-Index [4] [5]. The FAO developed rating systems, too. At first the Land

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Suitability Classification (LSC), developed in 1960 and focusing on natural conditions limiting the yield

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potential: Thermal and moisture regime, nutrient supply and relief as well as socioeconomic factors of the site.

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Hence, more emphasis is on rating of climatic and edaphic factors then soil rating itself. In a second project, the

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‘Agro Ecological Zones’, agro-climatic zones were combined with the already existing Soil Map of The World

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(1:5.000.000) to get suitability classes for different crops [4]. Furthermore, national soil ratings exist like the

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German ‘Amtliche Bodenschätzung’, rating the natural yield potential by soil properties, relief, climatic

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conditions and moisture regime [6]. From its basic it is a fiscal instrument but often used for agro-ecological

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issues, actually. To get an international consistent rating scheme the Soil Quality Assessment was developed in

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the USA. It focuses on small data sets of the evaluated soils to determine soil quality by only a few

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measurements [7]. A method explicitly accounting for the soil productivity of arable land as well as grassland is

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the Muencheberg Soil Quality Rating (M-SQR) [2]. For example, M-SQR was already applied extensively in

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Germany, based on soil maps (1:100.000) [8]. Furthermore, the practicability and reliability was confirmed by

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field tests in several countries and the rating scores are well correlated with crop yields, especially at a moderate

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level of farming intensity [3], as it is typical for the study area. The results of the M-SQR and the soil properties

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primarily concerning the yield potential are discussed here. By means of this rating, the arable productivity can

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be estimated on a global scale [8]. Hence, M-SQR was chosen for the purpose of this article.

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3.

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3.1. Location and climate

STUDY AREA

ACCEPTED MANUSCRIPT The Kazbegi study area is located in the Mtskheta‐Mtianeti region and aprox. 155 km2 in size (aprox. 270 ha are

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settlements). The Kazbegi district (population approx. 6,500) as an administrative unit stretches from the

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dividing Jvari Pass (‘Cross Pass’) to the Russian border (North‐Ossetia and Ingushetia) on the northern slope of

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the Great Caucasian Ridge. It is characterized by the valley of the Tergi (Terek) river and the Georgian Military

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Highway, one of the major routes crossing the Caucasus (Fig. 1). The main town Stepantsminda (‘Kazbegi’ in

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Russian, 1,850 m a.s.l.; population 1,700) is characterized by a moderately humid climate with relatively dry,

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cold winters and long, cool summers. The average annual temperature is 4.9 °C. January is the coldest month

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with an average temperature of ‐5.2 °C, while the maximum average temperature is 14.4 °C in July [9]. Besides

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Stepantsminda, the region is sparsely populated.

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Fig. 1 Location of the study area in N Georgia according to [10] (modified); total size of study area:

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154.94 km2

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3.2. Soil resources of the study area

ACCEPTED MANUSCRIPT Elevation of the study area is restricted to the montane to alpine zone [11]. The landscape morphology is diverse

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and shaped by quaternary fluvial and glacial sediments, Tertiary and Quaternary volcanic rocks and Jurassic

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sedimentary rocks [12][13][14][15]. The study area belongs to the geomorphological zone of the Tergi-Arguni

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interridge isoclinal depression (Kazbegi-Khevi intermontane basin) [16] and is characterized by high tectonic

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and geomorphologic activities. The Kazbek Neovolcanic center was still active in late Quaternary until less than

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50 k. y. BP. The last satellite volcano Tkasrsheti erupted in middle Holocene, approx. 6 k. y. BP. The

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stratovolcano Kazbek became a center of eruption with lava flows extended up to 15 km. Its lavas have a mixed

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mantle-crustal origin composition of mainly porphyry, rarely aphyric, rocks varies from basaltic andesites

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(basaltic trachyandesites) to dacites with a leading role of dacite lavas [17]. Three small explosive apparatuses

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are localized in the study area: near Pkhelshe, downward Sioni and at the mouth of the Chkheri River [17] NE’

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Stepantsminda.

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The second important bedrocks are flysch terrigenous and carbonate sediments of the complete Jurassic [16]

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(primary clay slates but also marlstone) and lower Cretaceous (limestone) [12][13][14][15]. The quaternary

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fluvial and glacial deposits are composed of both of these bedrocks. Due to this, a sediment cascade typical for

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the alpine geosystems [18] can be found in the study area: rock face, valley head (regolith), slope (debris/ talus

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fan), valley plain (alluvial sediments, terraces). Pediments are formed by sediment fans (e.g. talus) of Jurassic

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sediments or by slope loam and debris of volcanic rocks.

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Mudflows are a common natural hazard in Georgia (about 37 occurrences in the past 200 years), mainly due to

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intensive precipitation and consequent flooding with hot spots e.g. in the Tergi river basin [19]. However, due to

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[19] the study area is only in a zone of medium landslide hazard level. Furthermore, >70% of the territory of the

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Tergi river basin is subject to avalanches [20].

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Dominating soil types are Leptosols, Cambisols, Gelysols and Histosols [21]. Due to Urushadze [22] Mountain-

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Meadow soil (Leptosols) are spread in the study area (1,800 to 3,200 m a.s.l.), bordered by Leptosols (upper

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zone) and Cambisols (lower zone). These soils are characterized amongst others by acid and weakly acid

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reaction, a high content of humus as well as deep humus penetration [22]. As the study area is situated in the

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hypsometric level for (peri)glacial processes of the middle belt e.g. alpine to subalpine landscape (1,750 – 2,300

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m a.s.l.), slope (solifluction, rock-streams, snow avalanches, talus trains and mudflows) as well as plane

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(polygonal-structural) processes of periglacial morphogenesis prevail [20]. The soil-climatic conditions in the

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study area are characterized by a soil temperature at surface resp. at 20 cm depth of <10 resp. 0-10 °C during

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growing season as well as a reserve of productive moisture in the 1-m layer of 100-200 [mm a-1] [23] on a

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regional scale.

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3.3. Land use of the Kazbegi region

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Land use is characterized by the declining agricultural sector and rural poverty. Small natural forest remnants

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occur mainly on steep, northern slopes. During Soviet times, Pinus sylvatica stands were afforested in the

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vicinity of the villages to provide wood for the local communities [24]. Furthermore, due to Hansen et al. Betula

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litwinowii shrubbery is encroaching and has spread its distribution since 1987 by nearly 25% [25]. However, the

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subalpine and alpine areas in the region are dominated by grasslands. Accordingly, land use in the Kazbegi area

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was traditionally dominated by large‐scale pastoralism, which had its peak in terms of livestock numbers during

ACCEPTED MANUSCRIPT Soviet times when overgrazing led to severe erosion events [24]. Today, however, small herds of domestic cattle

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free‐range the vast, subalpine grasslands, while sheep husbandry has lost its former significance. Until Soviet

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times, the Kazbegi pastures were important summer pastures in a traditional transhumance system, which relied

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on winter pastures in the Nogay district in Northern Dagestan (Russia). Due to security concerns related to the

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conflict in Chechnya and the tensions between Georgia and Russia, this transhumance has been abandoned [26].

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Although the number of sheep has declined considerably from more than one million, there are still around

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20,000 sheep owned by local Kazbegi livestock owners grazing the subalpine and alpine grasslands (estimated,

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based on interviews of the former AMIES-project; unpublished data). While in soviet times even cereals were

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grown (Regional Museum in Stepantsminda, oral communication 2015), cropping is restricted to potato growing

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on small fields (mainly <1 hectare), today.

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4.

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MATERIAL AND METHODS

4.1. Soil quality rating

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Just a brief description of the M-SQR will be provided, for more details see [3] [27] [2] [28]: The M-SQR bases

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on the evaluation of properties of the rooting zone for cropping and uses indicators concerning the natural yield-

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potentials. These indicators are distinguished in 8 so called ‘basic soil indicators’ and 13 ‘soil hazard indicators’.

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While the basic indicators concerning criteria for plant growth (e.g. texture, rooting depth, wetness, ponding) and

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range from 0 (poorest) to 2 (best), hazard indicators concerning potential yield-limiting factor (e.g.

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contamination, acidification, drought) and range from 0.1 (maximum limitation) to 3 (no limitation). All basic

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indicators are summed up and multiplied by the lowest respective most limiting hazard indicator to get the final

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soil score (M-SQR score) between 0 (poorest) to 100 (best). Additionally, the M-SQR-score can be grouped in

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five classes from very poor (<20) up to very good (>80) and pedon rating can be transferred to landscapes. All

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basic indicators can be determined in the field preferably by a regular soil pit or otherwise a small soil pit

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(0.2*0.3 m and 0.4 m depth) and auguring at the bottom of the pit down to at least 1.4 m below surface. While

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some hazard indicators can be determined in the field (e.g. soil depth above hard rock, steep slope) others must

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be determined by evaluating the regional climatic data or laboratory data of soil analyses (e.g. salinity, total

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nutrient status). Hence, the final M-SQR-score integrates the field work, rating the pedon as well as the

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topography, climate data research and results of the laboratory work. A special aspect of the study was to

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investigate potential hazards of the food chain (hazard indicator No. 1 ‘contamination’ [2]) due to anthropogenic

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inputs or background concentrations of potential harmful substances or elements. Selected topsoils were

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analyzed for persistent organic pollutants (POPs) to get an idea of background concentrations by traffic and

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industrial emissions, application of plant protectants or due to ‘global distillation’ (also known as ‘grasshopper

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effect’). By ‘global distillation’, POPs are transported from emission areas to cooler regions via the atmosphere:

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Recurring volatilization and cold condensation ultimately result in accumulation of POPs in cold regions, i.e.

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high mountains and Polar Regions [29]. In these regions, POP concentrations are found to increase with altitude

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as a result of the cold-trapping effect and accumulate in forest soils near the tree-line, which is attributed to the

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filter effect of trees. Recently, these phenomena were observed in mountainous regions of Europe, North

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America and in the Himalaya [29] [30]. Furthermore, a low phosphorous availability is a well-known

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ACCEPTED MANUSCRIPT phenomenon of soils from volcanic parent material [31]. Hence, phosphorous sorption was comparatively

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investigated on selected soils from volcanic as well as non-volcanic parent material referring to hazard indicator

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No. 5 (‘low total nutrient status’).

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For this study the basic parameters were determined in the field while most of the hazard indicators were

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deduced from results of the laboratory analyses described below.

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To get an exact idea of soil distribution in landscape, geomorphological as well as geological representative

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areas were chosen for mapping of catenae, consisting of up to four profiles in different relief positions, while the

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interspace between the profiles was mapped with augers of 1 m depth. In total 43 soil pits and 32 augers were

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investigated in July and August 2014 and 2015. Soil mapping in field was conducted due to [32] as well as

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Error! Reference source not found. according to [3], representative mixed samples were taken from every soil

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horizon for determination of physical and chemical parameters (see below). SQR was conducted on 36 profiles

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(regular soil pits) and 3 augers due to [2] and [28] (adjusted climatic hazards). Highest soil exploration was

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located at 2.421 m a.s.l. (P23, N’ Juta) and lowest at 1.760 m a.s.l. (B24, E’ Pansheti). As SQR distinguishes

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between grassland and arable land, actual land use was documented. Hence, change of land use might lead to a

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different scoring.

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A further task was the creation of a synthetic soil quality map based on the surveyed profiles as well as soil

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substrate, inclination, elevation and aspect (based on a digital elevation model, cell size 20*20 m). Taking into

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account the SQR-factors ‘slope and relief’ as well as the hazard indicator ‘steep slope’, mapped SQR-

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Classification was additionally adapted to inclination. As a result soils in an area with >15° inclination were

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scored as ‘(very) poor’, regardless of soil type or substrate. In case of the parent material ‘volcanic influenced

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unconsolidated rocks’ (see below) a further restriction was made: so a ‘moderate’ or better rating is restricted to

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areas with an inclination <10°. For cartographic depiction ArcMap 10.2.1 (ESRI Inc.) was used.

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Soil samples for chemical and physical analyses were dried at 40°C, sieved for 2 mm, partially finely ground in a

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hand mortar and stored at room temperature until analysis. Partly, field fresh samples were also frozen (-30 °C)

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for analyzing POP. Soil pH was measured in suspension of soil and 0.01 M CaCl2 with a ratio of 1:2.5 [33].

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Electric conductivity was measured in suspension of soil and deionized water with a ratio of 1:2.5 [35]. Contents

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of carbonates were determined by the gas-volumetric method using a calcimeter [36]. The total amount of carbon

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(Ct) was determined by a C-N-S element analyzer (Elementar). Inorganic C was calculated from the carbonate

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content by using the factor 0.1199, while the amounts of Corg result from the difference between Ct and inorganic

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carbon. Particle size distribution was determined by a combined sieving (sand and coarse silt fractions) and

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pipette method (medium silt and clay fractions) after decomposition of carbonates (HCl) and organic matter

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(H2O2) and dispersion in Na-Pyrophosphate [[37]]. The (pseudo-)total content of elements was extracted with

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aqua regia (3 parts 32% HCl and 1 part 65% HNO3) and microwave extraction from finely ground samples [38]

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[39]. As the total content is not sufficient to determine eco-toxicologically relevant trace metals, the mobile and

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exchangeable fraction (potentially plant available and easily leachable) was also extracted with 1 M NH4NO3

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[40]. All extracts were stored in polyethylene bottles until analysis. Element concentrations were determined

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with ICP-OES (Agilent Technologies, Modell 720ES). Plant-available inorganic P and K was extracted by the

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ACCEPTED MANUSCRIPT CAL (Ca-acetate-lactate) method using a spectral photometer (T80 UV/VIS Spectrometer, PG Instruments Ltd.)

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[41] for P, resp. an atomic absorption spectrometer (AAS) (FAAS 4100, Perkin Elmer) for K. Potential CEC was

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determined at pH 7.2 with 0.1 M BaCl2, measuring Al3+, Ca2+, Mg2+, Mn2+, Na+, and K+ [42]. Organic pollutants

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were extracted and measured by soild-phase microextraction (SPME) coupled to GC/MS (ITQ, Thermo). 500

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mg of soil were weighted to 20 mL brownglas headspaces vials with 10 mL of 0.01 M CaCl2 solution. To

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enhance extraction, 10% NaCl was added. Quantification was performed with external standard calibration and a

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validation with soil samples of known pollutant concentration. SPME extraction was performed in headspace

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mode with 100 µm PDMS coated filters (Supelico). With this approach, concentrations >50 µg kg-1 can be

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determined (quantification limit).

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For climatic issues of the M-SQR (hazard indicators no. 7 and 12 ‘drought’, ‘unsuitable soil thermal regime’)

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data of the Department of Hydrometrology from 1961 to 1990 [43] were used. For deduction of the hazard

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indicator ‘contamination’ background concentrations of trace metals and organic pollutants/chemicals typical for

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Georgia (PAH, DDx, HCH, PCB, Dieldrin, Aldrin, Endosulfan I and trifluralin) were chosen.

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Phosphate-adsorption was determined according [44] by measuring the P-sorption of 0.5-1.0 g fine earth <2 mm

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from batch-solutions with defined phosphorous concentrations (0 up to 275 mg l-1).

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5.

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RESULTS AND DISSCUSSION

5.1. Soil Quality Rating

For the purpose of evaluating and classifying soil quality, a classification by soil types due to Error! Reference

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source not found. proved difficult, because Cambisols and Umbrisols developed on stony sediments fans as

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well as on volcanic influenced substrates with very different properties and yield potentials. However, due to the

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dependency of soil quality from soil substrate (see below) a rough classification due to the six main parent

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materials of pedogenesis of the study area was developed. The general term ‘parent material’ is used, because

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different substrates might be included, e.g. loam or even gravel in case of fluvial deposits. For practical reasons

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and for sake of clarity, such a simplification is appropriate. The results are summarized in Table 1 and discussed

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in the following.

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Table 1: Muencheberg Soil Quality Rating (SQR), agricultural potential and soil type (dominating type

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underlined) as a function of parent material; amedian // minimum – maximum; b median //arithmetic mean and

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standard deviation; n.a.: not analysed; (): small sample size

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226 Parent

Solid rock

Material

Debris of

Glacial

Volcanic

Fluvial

Jurassic

sediments

influenced

sediments

sedimentary

(pumice, ashes)

rocks

unconsolidated

Peat

rock Soil types

Leptosol

Skeletic

Umbrisol/

Umbrisol/

Fluvisol,

Histosol

ACCEPTED MANUSCRIPT

SQR-class

Very Poor

Regosol,

Cambisol,

Skeletic

Regosol

Cambisol

Fluvic Cambisol,

Cambisol/

Regosol

Umbrisol

(Fluvic)

(Very) Poor

Poor

– Moderate

Moderate

–

(Very Poor) –

(Very) Poor

Moderate

– Moderate

–

Moderate

Steep

High

High

Acidification /

e.g. hazard

slope/

percentage

percentage

Low total

factors (except

High

of coarse

of coarse

nutrient status,

thermal

percentage

soil texture

soil texture

especially

regime) [2]

of coarse

fragments

fragments

phosphorous

High

Flooding

percentage

and extreme

of coarse

waterlogging

soil texture

fragments /

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Main limiting

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(Good)

soil texture

Flooding

fragments

and extreme

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waterlogging

Actual land

(Forrest,

Forrest,

Forrest,

Forrest, Pasture,

Pasture,

Pasture,

use

Pasture)

Pasture,

Pasture,

Meadow,

Meadow,

Meadow

Meadow,

Meadow,

(Cropping)

(Cropping)

(Cropping)

(Cropping)

pH-value1 (6.5)

5.0-7.2

3.9-6.1

4.3-6.9

5.0-7.4

(6.9)

Subsoil

n.a.

4.3-7.4

4.0-5.1

4.0-5.1

5.1-7.5

(4.5-5.1)

Underground

n.a.

4.7-7.4

4.3-6.9

3.8-5.8

5.2-7.7

(2.6-3.6)

(11,2)

7.9 // 2.7-

14.2 // 6.7-

9.0 // 5.2-13.9

4.2 // 0.8-6.8

(28,6)

16.7

17.7

2.7 // 0.4-5.2

1.3 // 0.9-2.3

(25.5)

Topsoil

Subsoil

n.a.

2.3 // 0.6-5.1

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Dominating

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Corg [%]a

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Topsoil

1.0 // 0.66.0

texture class (FAO)

Topsoil

(SL)

L

LC

L

SL

-

L

SL

SL/SiL

SiL

-

14.8 //

20.1 //

83.0 //

8.8 //

(11.3)

28.5±27.1

25.7±8.2

31.0±19.6

9.8±4.9

(29.3)

(7.5)

4.0 //

8.7//

0.5 // 4.9±6.0

1.4 //

(1.0)

Subsoil

Nutrient content (Profile)b K [g m-2] -2

P [g m ]

ACCEPTED MANUSCRIPT 7.6±8.6

7.8±1.7

1.7±2.1

7.6 //

11.2 // 16.8

2.9 //

7.9±4.0

±8.1

1,899.3 //

4,093.9 //

1,855.4±110 (501.0) C:N (Topsoil) N profiles

-2

Nmin [g m ]

7.9 // 9.0±4.5

2.6±1.3

3,725.7±57

2,520.0 //

776.7 //

3.9

3.4

2,210.6±1,499.2

820.8±607.3

(2,392.2)

(11:1)

11:1

10:1

10:1

14:1

(1:16)

1

11

4

15

Nres. [g m-2]2

(4.8)

RI PT

(1.8)

7

1

No averaging, due to aggregation of substrates with different basicity

228

2

Nres = Nitrogen-reserve, based on total N [%]

229

A general characteristic of all soils of the study area is the high Corg content in combination with a narrow C/N-

230

value. Hence, nitrogen supply is mostly on a high or very high level [44]. Most of the soils show a low bulk

231

density, in some cases even down to 0.5 g cm-3 (Ah-horizon of P22, a Cambic Umbrisol on glacial sediments)

232

due to the high content of Corg and the stabile crumbly soil structure. By contrast, the phosphorus supply is a

233

limiting factor in nearly all soils, independent from parent material. In addition, potassium deficiency is a

234

problem, though less severe.

235

Furthermore, drought or too cold climate conditions are the critical hazard indicators [28]. Due to the relatively

236

high precipitation of 442 mm during the vegetation period (May to August), there is no risk of drought.

237

Nevertheless, an ‘unsuitable thermal regime’ is a general SQR-hazard indicator due to a mean annual

238

temperature of 4.9°C (see above) resulting in a lower graduation for arable land [28]. The soil thermal regime is

239

critical for germination. Most grasses germinate at temperatures above 5°C, while crops need for germination

240

temperatures between 5 and 10°C [28]. However, due to the increased radiation budget SE to WW exposed

241

slopes are characterized by a more favorable microclimate, leading to an extended vegetation period of 2 to 3

242

weeks (Otte, oral communication 2016).

244

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1

5.2. Properties of the parent materials Soils of the alpine ecosystem are regarded to be shallow, rocky, and mostly used as pasture. Indeed, we find such

246

soils largely extended in the study area. However, they are not as characteristic for the Kazbegi region as they

247

seem to be at the first sight. On very steep slopes with an inclination >30° or on exposed slope areas soils above

248

solid rock, maybe underlain by a shallow regolith layer only, are widely spread (45.55 km2 or 29% of the study

249

area) especially in higher elevations at the transition zone from pediment to the open rock surface. Due to Error!

250

Reference source not found. such soils have to be classified as Leptosols (partly Humic). Depending on coarse

251

fraction and bedrock the qualifiers (Hyper)Skeletic and/or Calcaric might be prefixed. Obviously due to the

252

shallow root zone and steepness that influence further soil parameters, e.g. water capacity or thermal regime, an

253

agricultural potential is strongly limited or nonexistent. Due to limited access and the assumption of a spatially

254

homogenous soil development from such parent materials, only one example profile (P44, close to Akhaltsikhe)

255

was classified with M- SQR, resulting in only 11 points or ‘Very Low’. Even if in some areas site conditions are

256

slightly better, e.g. a deeper regolith layer, it can be assumed that these soils belong to the M-SQR-class ‘very

257

low’ due to steepness, shallow profile, low nutrient status as well as small water capacity. Hence, only fallow,

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245

ACCEPTED MANUSCRIPT extensive pasturing or the use of extensive forestry is possible, strongly connected to accessibility and steepness,

259

but erosion control must have highest priority, because the unconsolidated rocks at steep slopes of the study area

260

are exposed to mud slides like incase of the mud slide in Mleta in 2010 [45].

261

Hence, below the Leptosols above solid rock deeper soils can be found on weathered debris. It has to be

262

distinguished between soils formed on accumulated debris from the Jurassic sedimentary rocks and soils formed

263

on parent material, which was more or less mixed with pyroclastic materials. The soils mentioned first are very

264

rich in stones with up to 75% coarse fraction in the subsoil resulting in a low water capacity combined with

265

limited nutrient supply and difficult conditions for cultivation. However, due to the loose substrate, roots can be

266

found down to more than 1 m. Most of the settlements in the study area, e.g. itself, are built on these debris fans.

267

Hence, main SQR-hazard indicators are, beside the thermal regime that is a problem for all soils in the study

268

area, ‘high percentage of coarse soil texture fragments’ and ‘steep slope’. Chemical alteration of the subsoil is

269

partly masked by the primary dark rock color of slate debris. If chemical alteration can only be traced in

270

laboratory by analyzing crystalline and amorphous iron oxides these soils are no Cambisols as described by

271

Urushadze et al. [Error! Bookmark not defined.]. Instead of this, they have to be classified as Regosols. Under

272

intensive cultivation in house gardens or fields close to the settlements, Hortisols have developed as well. They

273

are characterized by a high content of Corg, accumulated in the topsoil. However, the blackish color is not only

274

the result of humus accumulation, but results also from lithogenic carbon of the Jurassic silt stones and clay

275

slates. These soils cover 5,039 ha or ca. 32.5 % of the study area. The agricultural potential due to SQR ranges

276

from very poor in case of steep slopes and/or a high proportion of coarse fraction, to moderate on lesser steep

277

parts of the sediment fans.

278

Concentrations of primary nutrients differ, while (in non-cultivated soils) potassium and phosphorus reserves of

279

the profiles are low [44], nitrogen reserves as well as actually available nitrate and ammonia are mostly (very)

280

high due to the high humus content, high mineralization rates and low leaching rates during the dry phases of the

281

vegetation period. Therefore, most of these soils, even with a good accessibility, are used as pasture, hay

282

meadow or small potato fields. At least in case of soils on the lower parts of the sediment fans, this kind of land

283

use is far below their potential. This also becomes evident if the former land us is taken into account: In the

284

second half of the last century barley was grown on a large scale on the lower parts of the sediment fans close to

285

Stepantsminda (Regional Museum in Stepantsminda , oral communication 2015).

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ACCEPTED MANUSCRIPT

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287

Fig. 2 On debris fans of the Jurassic sedimentary rocks (mainly slates), profound but skeletic soils have

289

developed; P12 Skeletic Regosol (Humic) from Jurassic clay slate on a sediment fan, SE of Stepantsminda, M-

290

SQR rating 43 points (class: moderate), used as pasture below a former potato field.

291

The third main group of soils has developed on pediments and plateaus from Andesite-Dacite and other

292

pyroclastics (e.g. tuff). This parent material (‘volcanic influenced unconsolidated rock’) covers 2,518 ha or ca.

293

16% of the study area. Depending on base saturation, Cambic Umbrisols or Cambisols (Humic) have developed.

294

It is obvious that in case of steep slopes also on this substrate only very low or low SQR-rated soils developed,

295

e.g. P17 (19 points). But on smooth slopes or in flat areas moderate to good SQR-classes are distributed. These

296

are by far the best soils of the study area, especially if they have developed on colluvial loam in accumulation

297

areas (e.g. slope toe). We found rooting even down to nearly 2 m below surface. For example the Umbrisol

298

(Protoandic Colluvic Hyperhumic) (P05, see Fig. 3) roughly in the middle of the volcanic plateau close to the

299

village Ukhati gets 79 points, that is on the upper edge of the SQR-class ‘good’.

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301

ACCEPTED MANUSCRIPT Fig. 3 Umbrisol (Colluvic Hyperhumic Protoandic) above Gleyic Umbrisol, from colluvium above glacial-

303

fluvial sediments above colluvium, pasture; P05 W’ Ukhati, SQR rating 79 points (class: good).

304

Except of the thermal regime acidification could be problematic in a few cases, because soil pH in most profiles

305

is >4.5. Furthermore, phosphorus availability might be limited (referring to SQR-hazard indicator ‘low total

306

nutrient status’) if the soils show protoandic properties Error! Reference source not found.. These result in an

307

increased phosphate-fixation by allophanes and metal-humus complexes, due to a high anion exchange capacity.

308

This could also be a problem for other anionic nutrients (e.g. nitrate or chloride) [31]. In Table 2 the

309

phosphorus-retention of three different soils is shown. A Cambic Umbrisol (Protoandic) (P07) has developed on

310

slope loam over Andesite-Dacite (close to Ukhati), while a Cambisol (Humic Tephric) (P16) has developed

311

directly on significantly younger (very likely from Holocene) and only weakly weathered tephra (close to Sioni).

312

In contrasts, A Cambisol (Humic) (P11) has developed on debris of clay slate (above Stepantsmida). P07 shows

313

a dramatically higher phosphorus-retention than P16 due to the formation of Fe- and Al-oxides in the Umbrisol

314

of P07 by weathering of silicates, with a significant proportion of allophanes and ferrihydrite (see Tab. 2:

315

Alox+1/2 Feox), certainly. Hence, cropping may need an increased phosphorus-fertilization combined with liming

316

to increase soil-pH and to decrease anion exchange capacity.

317

Table 2: P-sorption of two soils on volcanic influenced unconsolidated rock (P07, P16) and one on debris of

318

Jurassic sedimentary rocks; Alox+1/2 Feox [mg kg-1] = active oxides [44], diagnostic criteria due to Error!

319

Reference source not found.

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302

Added P [mg l-1)

Sorbet P [%]

Alox+1/2 Feox [mg kg-1]

P07 / Ah2 (Cambic Umbrisol

25 100 250 25

100 93 61 100

10.306

Protoandic) P07 / Bw-Ah

AC C

P16 / Bw

P11 / Ah (Cambisol Humic Tephric)

P11 / Bw

100 250 25 100 150 25

95 64 17 5 3 28

100 150 25 100 150 25 100 150

11 7 76 37 27 68 35 22

EP

P16 / Ah (Cambisol Humic)

TE D

Profile/horizon

12.815

5.335

4.710

1.087

1.599

320 321

Within the Pleistocene major parts of the study area were covered by glaciers, as it is easy to conclude from the

322

shape of valleys and the distribution of end and side moraines, e.g. in the Truso valley. Hence, soils developed

323

on glacial deposits partly covered by Holocene deposits. For example in the Chkheri valley, WNW’

ACCEPTED MANUSCRIPT 324

Stepantsminda, a groundmoraine is buried beneath late-glacial fluvial sediments or at the Ukhati plateau by

325

colluvium (P05, P36; see Fig. 6). Hence, only a total area of 398 ha, or less than 3% of the study area, various

326

glacial sediments are the parent material of the complete soil. However, in other soils they participate as layers in

327

deeper parts. A typical hazard indicator for these soils, mostly Cambisols or Umbrisols but also Calcaric

328

Regosols, is a ‘high percentage of coarse soil texture fragments’ due to bed load of the moraines.

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329

330

Fig. 4 Cambic Umbrisol (Hyperhumic) (P23 N’ Juta, see Fig. 6) as a typical soil on an endmoraine, with a high

332

content of organic matter and fine earth, but rather shallow. Land use 2015: pasture; M-SQR rating 40 points

333

(class: poor).

334

Fluvisols or soils with fluvic properties cover 2.081 ha or ca. 13% of the study area. These soils are formed on a

335

variety of substrates, depending on source area of the watercourse as well as distance to the water divide. Due to

336

dominating calcareous sedimentary rocks in the south of the study area, most alluvial sediments are calcareous.

337

Water logging and ponding up to paludification is a problem in case of the braided river beds of the Truso river

338

(below Ukhati) and the Snotskali river (SE Akhothi), resulting in the SQR-hazard indicator ‘flooding and

339

extreme waterlogging’. However, the main hazard indicator ‘high percentage of coarse soil texture fragments’ is

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ACCEPTED MANUSCRIPT a result of postglacial outwash as well as mass movements on slopes in the study area, especially at the low

341

terraces.

342

Fig. 5 Depending on the substrate yield potentials of the Fluvisols differ within a broad range: a) Calcaric Gleyic

343

Fluvisol (P03, see Fig. 6), on haugh, Truso valley, SQR rating 50 points (class: moderate); b) Calcaric Skeletic

344

Regosol (Humic Fluvic) (P29, see Fig. 6), on coarse gravel and rubble, pasture; NE’ Achkhoti, SQR rating 34

345

points (class: poor)

346

Histosols occur in isolated and small areas in abandoned braided river beds, e.g. between Achkhoti and Sno (ca.

347

2 ha in size, see Fig. 6), or slope flattenings above an aquiclude, e.g. at the counter slope S’ Ukhati (see Fig. 6).

348

Bogs are not taken into account of the SQR-map due to the small size of the areas. Generally, similar restrictions

349

for cultivation apply as in case of the Fluvisols with an extreme water regime as mentioned above. For example

350

the drained low-level moor between Achkhoti and Sno is used as a meadow in 2015.

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340

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ACCEPTED MANUSCRIPT

351 352

Fig. 6. Map of the SQR-Score [2] of the study area, in case of the Jutistkali River no fluvial parent material is

353

shown separately, due to dominating slope processes in the steep gorge.

355

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5.3. Hazard indicator ‘contamination’ [28]:

Due to the aim of the study to supply information for a sustainable agricultural and horticultural land use

357

particular care has been given to the hazard indicator ‘contamination’. For this purpose trace metals as well as

358

organic pollutants/chemicals were measured in selected samples.

359

Trace metals increase in soils on bedrocks containing high lithogenic amounts. This is the case for sedimentary

360

resp. metamorphic as well as volcanic rocks [46]; both are more or less sources of all soil forming substrates in

361

the study area. The andesite and dacite lavas of the Kazbek nevolcanic center show e.g. Ni and Cr concentrations

362

of 15-150 resp. 30-270 [mg kg-1] [17].

363

In Table 3, selected trace metals in the topsoil horizons of the soil explorations as well as further sampling

364

points are shown. In a few case total concentrations exceed Georgian thresholds [47]. However, mobile forms

365

are relevant for risk assessment. Due to this 10 % of the samples, covering the range of metal concentrations,

366

were extracted with 1 M NH4NO3-solution to evaluate mobile species. As expected, only a very small part of

367

total concentrations belongs to the mobile fraction. Hence, elevated trace metal concentrations can be traced

368

back to lithogenic background concentrations which cause only a very small risk for a translocation into food

369

chain.

370

Table 3: Selected trace metals in the Ah horizons of soils of the Kazbegi region

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ACCEPTED MANUSCRIPT Trace Metal

Min

Max

[mg kg-1]

Arithmetic mean,

Median

standard deviation1

Georgian

N

Mobil form2

threshold (clay, pH <5.5)

3.80

33.30

12.61±7.87

11.57

5

44

<0.1%

Pb

4.84

47.64

18.81±10.14

13.26

65

44

<0.2%

Co

4.97

47.34

15.18±8.24

14.25

-

44

<0.1%

Cu

14.48

127.42

36.21±21.75

30.75

66

Ni

18.77

73.19

40.47±13.65

39.81

40

Zn

34.56

191.70

95.23±36.32

78.78

110

1

Aqua regia-extraction

372

2

1 M NH4NO3-extraction

44

<0.4%

44

<0.1%

44

<0.2%

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As

373

A further task was the evaluation of POPs in topsoils due to industrial and traffic emissions or application of

375

plant pesticides. In topsoils of three (former) glass houses in Kazbegi region we found residues of DDT and

376

HCH resp. their metabolites (data not shown), presumably due to application in Soviet times. In one case the

377

Georgian threshold for DDT was exceeded [47]. Due to this, 22 topsoils of the investigated profiles were chosen

378

for a screening on POPs.

379

However, in the investigated soils, all measured substances were below the quantification limit of the screening

380

method used. Hence, neither inorganic nor organic pollutants can be found in relevant amounts in outdoor

381

topsoils of the study area. Due to this, the hazard indicator ‘contamination’ can be excluded for all investigated

382

soils. Nevertheless, for precautionary reasons the still intensively used topsoils of the (former) glass houses

383

should be investigated in more detail.

Table 4: Persistent organic Pollutants in the topsoils of the Kazbegi region (mixing samples of A-Horizons) Substance

Use/

4.4 DDE; 2.4-, 4.4-

EP

385

Quantification

N

Detected

-1

Source

limit [µg kg ]

metabolites/ insecticides

50

22

-

e.g. trans-formators, hydraulic engines

50

22

-

incomplete combustion of organic matter

50

22

-

α, β,γ and ∆-HCH

Technical mixture, Insecticide (γ),

50

22

-

Dieldrin

Insecticide

50

22

-

Aldrin

Insecticide

50

22

-

Endosulfan I

Insecticide, acaricide

50

22

-

Trifluralin

Herbicide

50

22

-

DDT; PCB PAH

2.4-,

4.4

AC C

DDD;

386

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384

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ACCEPTED MANUSCRIPT 387 388

5.4. Yield potential and appropriated crops: Soils with a poor (or even very poor) yield potential are rated with less than 20 and up to 40 M-SQR-points.

390

From all 39 soil explorations 21 fall into this category. These soils are suitable for grassland and (if ≥20 SQR-

391

points) for crops adapted to local conditions for subsistence farming [2]. Due to hazard indicators like ‘soil depth

392

above hard rock’, ‘flooding and extreme water logging’ or ‘steep slope’ cropping is strongly limited. While

393

excess water is limited to the Fluvisols in floodplains resp. Histosols, inclination of slopes and soil depth pose a

394

problem to all soils. But due to the further hazard indicator ‘High percentage of coarse soil texture fragments’

395

soils on ‘debris of Jurassic sedimentary rocks’ are disproportionately represented (7 of 10) in this class. Sites not

396

that much restricted by inclination are suitable for cropping in case of an adequate soil management (erosion

397

control, fertilization).

398

Suitable soils with a low yield potential for cropping, developed from ‘volcanic influenced unconsolidated rock’

399

are distributed e.g. on the smooth to middle steep slopes above Ukhati. Soils from ‘debris of Jurassic slates’ are

400

distributed on the unforested slopes N’ and S’ Stepantsminda.

401

If these soils are deep enough cereals could be cultivated to improve local food supply as well as local markets

402

e.g. for sustainable tourism. Many abandoned terraces indicate where grain was formerly grown in the Khevi

403

region [48] (Kazbegi). Arable crops adapted to local conditions could be Oat (Avena sativa L.), Summer-Barley

404

(Hordeum vulgare var. distichon L.) [48] and Solanum tuberosum L. [50] (list is not exhaustive; variety trials are

405

necessary). Nevertheless, erosion control must have highest priority. Furthermore, particularly rare soils, like the

406

Cambisols on Tephra close to Sioni (P 16, see Fig. 6), should be protected e.g. in form of geotopes.

407

Secale cereale shows the broadest ecological adaptability, due to its few demands on soil quality and climate

408

[48] [51]. Caucasian rye (S. cereale L.) used to be cultivated in high mountain regions of Georgia (1.800-2.200

409

m) and entered into bread and beer production [48]. Actually S. cereale L. is only a local cultivar of high

410

mountain regions of Georgia and fields are now found only in Upper and Lower Svaneti (north-western

411

Georgia) and Meskheti (south-western Georgia) [52]. However, heavy rainfall, typical for the vegetation period

412

in the study area [43], could be a problem for the stability of the long haulms of S. cereale [48].

413

H. vulgare var. distichon is a summer culture due to the limited frost hardiness of winter barley of only -12 °C

414

[53]. For summer barley the climatic preconditions, as vernalization temperature (5 to 10 days of max. 10°C) and

415

frost hardiness (-6 °C) are fulfilled [54]. Nevertheless, pH-value should be above 6, because summer barley is

416

sensible to a lower pH [50]. This might be a problem for most of the soils and therefore liming would be

417

unavoidable. H. vulgare is an ancient agricultural crop in Georgia and had particular importance in beer

418

production [48]. Avena sativa could be a further alternative cereal but it has only a limited functionality for food

419

supply. Its frost hardiness is similar to H. vulgare but it is less sensitive to low pH-values [54], also its root

420

system is more effective [50].

421

Solanum tuberosum could be an alternative on shallower soils or soils with a coarse fraction. It is highly

422

adaptable to soil quality and climate and grows on soils with a pH-value down to 3.7 [50]. Cultivation is possible

423

up to 2.000 m a.s.l. and soils from sandy loam or loamy sand rich in humus are most suitable, while a higher clay

424

content reduces yield [50]. It is already cultivated to some degree in the study area, even on the volcanic plateau

425

of Ukhati >2.000 m a.s.l..

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ACCEPTED MANUSCRIPT 426 Soils with a moderate yield potential are rated between 40 and 60 M-SQR-points. From all 39 soil explorations

428

17 fall into this category. These soils, mainly developed from glacial sediments or volcanic influenced

429

unconsolidated rock, are also classified as ‘unique farmland’, characterized by a lower quality than ‘prime

430

farmland’, [55]. Due to [56] the strongly represented Umbrisols can be improved drastically by erosion control,

431

fertilization (N, P, K, Mg) as well as adapted cropping (potatoes, cereals). In addition to the above notified crops,

432

cropping of Triticum aestivum L. or other Tritium species might be possible in a few cases, e.g. on Fluvisols

433

from alluvial loam in the Truso valley (cp. Fig. 5). Nineteen species of wheat from the 26 known species of the

434

genus Triticum have been historically distributed in Georgia [52]. Summer wheat can be cultivated up to 2.000 m

435

a.s.l. with best results on calcareous, humus-rich soils [57], like the Fluvisols mentioned above. However, T.

436

aestivum needs a dry period for grain maturity. Hence, due to only short dry periods during vegetation period

437

(max. 9 days due to [43]) yield could be less than regular. Wheat fields were planted throughout Georgia at

438

elevations from 300 m to even 2.160 m a.s.l.. Almost none of these traditional wheat varieties and species occur

439

in the territory of Georgia, actually. Nevertheless, endemic T. carthlicum, that is adapted to high elevations, is

440

still grown in the mountainous area of Meskheti [52].

441

However, cropping is restricted to the lower areas of the study area even on these soils. Furthermore, liming is

442

necessary for most soils as well as an appropriate erosion control. Soils on higher areas should stay pastures or

443

meadows, even in case of a moderate yield potential e.g. soil on glacial sediments around the village of Jutha.

444

Soils with a high yield potential are rated between 60 and 80 SQR-points. From all 39 soil explorations only 1

445

site falls into this category. These high quality soils are restricted to loamy colluvium at the volcanic plateaus in

446

the study area, e.g. Ukhati, Toti or Tsdo. Despite their altitude (>2.000 a.s.l.) and difficult accessibility, these

447

soils are predestinated to improve productivity of the local agriculture. Due to their location in the landscape

448

(accumulation area), erosion is less problematic but amelioration (liming) is still necessary due to the low pH

449

(see Table 1).

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427

To check the plausibility of the modeled SQR-map, it was compared to a map of grassland yield, developed by

452

Magiera et al. [58], which is based on extrapolated species composition, represented by metrically scaled

453

variables in form of ordination axes. As predictive variables for plant species composition, vegetation indices

454

from Rapid Eye imagery and environmental variables from a digital elevation model were used. As a result a

455

higher yield fit well with higher M-SQR-scores. In a few cases, e.g. the N’ slope of Truso valley, higher yield

456

correspondences with a low SQR-score, as steep slopes lead to a low SQR-score but do not have that massive

457

impact on the productivity of grassland. Hence, practical applicability of the SQR can be taken for proven.

458

However, the map cannot simply be adopted as concrete options for small-scale planning. Due to the high spatial

459

heterogeneity of substrates and morphology of the study area, site specific validation has to be carried out first.

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460

461

6.

CONCLUSIONS

462

Most limiting factors are climate as well as steepness, while the low nutrient supply and soil acidity can be

463

tackled by adequate fertilization and liming practice. Inorganic or organic pollutions were not detected. Soils on

464

sediment fans (debris of Jurassic sedimentary rocks) as well as glacial sediments, mostly Cambisols (Humic), are

ACCEPTED MANUSCRIPT characterized by a low to moderate fertility while high-yield soils, mostly Cambic Umbrisols, can be found on

466

volcanic plateaus, e.g. around the abandoned villages of Ukhati and Toti. Actually, most of them are used only

467

for pasture, due to poor accessibility. To exploit the moderate up to good potential fertility, road transport

468

infrastructure has to be optimized. Soils on fluvial deposits (mostly Fluvisols) show a very high range of SQR-

469

scores. In case of loamy alluvial deposits cropping is a suitable land use (as it is partly already practiced), but

470

most of the banks are characterized by gravel-rich deposits, suitable only for pasture. Due to climate and soil

471

conditions, the most adequate crop is Solanum tuberosum L. Further cereals with respect to local conditions are

472

rye, summer barley or even summer wheat. However, heavy rainfalls could cause harvest losses and water

473

erosion and that is why the cultivation of cereals was given up and replaced by grassland management with cattle

474

and sheep. Due to this, soils with a moderate SQR-Score but a high erosion risk should remain grassland.

475

Altogether, the soils of the study area have the actually untapped potential to optimize the basic supply of the

476

local population as well as tourism also by cultivation of some special cereals. Nevertheless, variety trials on

477

different soil forming substrates are major preconditions for successful implementation of new cropping systems

478

in the Kazbegi region. Furthermore, particularly rare soils, e.g. Cambisols on Tephra, should be protected. 7.

479

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Acknowledgements

480

The authors wish to thank the Volkswagen Foundation for financing the project, Dr. B. Vashev for his intensive

481

support in field, M. Schatz and L. Böhm for their diligent support in POP-analytics, N. Mayerhofer for his

482

support in P-sorption experiments and Prof. Dr. A. Otte for the fruitful discussion and support as well as the

483

anonymous reviewers for their helpful comments.

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