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В странах Средней (Центральной) Азии также не сложилось единое мнение по этому вопросу. Исследователи почв арчевников называют их по разному или же относят их к различным почвенным типам, подтипам: черноземовидным, особым лесным темноцветным, горно-лесным почвам арчевников, перегнойноторфянистым или светло-коричневым бурым, коричневым [4, 6].

Первая классификация почв Кавказа, в том числе Азербайджана, дана профессором С.А. Захаровым в 1927 году. Большая работа в области изучения почв Большого Кавказа в пределах Азербайджана была проделана академиком Г.А. Алиевым [1]. Совместно с С.Г. Халиловым и Р.М. Абдуевой, им также была проведена большая работа по определению генетического типа преобладающих в аридных редколесьях коричневых почв и ряда сопровождающих их почв полупустынных и степных ландшафтов [2].

Мы также придерживаемся точки зрения о том, что на территории аридного редколесья Азербайджана сформировались коричневые почвы, которые несколько отличаются по некоторым показателям от коричневых лесных почв, формирующихся под ксерофильными широколиственными лесами, в частности, меньшим содержанием гумуса, большим содержанием карбонатов и т.д.

В области Большого Кавказа аридные леса низкогорья занимают восточное, северо-восточное окончание Гусарской наклонной равнины и южный склон Аджиноурских низкогорий. Самый крупный в Азербайджане массив фисташко- во-можжевеловых редколесий охраняется на территории Турианчайского Государственного Природного заповедника [7].

Мы в течение ряда лет проводили исследования почв аридных редколесий Большого Кавказа на вышеуказанных территориях. Некоторые полученные данные отражены в нижеследующей характеристике.

Горно-лесные коричневые выщелоченные почвы распространены отдель-

ными пятнами на северных склонах или в более увлажненных условиях, связанных с микрорельефом местности. Характерными морфологическими признаками коричневых выщелоченных почв являются: четкая структурная дифференциация профиля, а также глубокое залегание карбонатного горизонта. Содержание гумуса

вверхнем горизонте этих почв составляет 2,4-5,0%. Содержание азота коррелирует с содержанием гумуса и составляет в слое 0-20 см 0,16-0,33%. Реакция среды в верхних горизонтах близка к нейтральной (6,7-6,9), в нижних горизонтах немного повышается и в слое 0-100 см составляет 7,0-7,3. Сумма поглощенных оснований

вверхнем горизонте от 19,50 до 36,80 мг-экв/100 г почвы.

Горно-лесные коричневые типичные почвы в основном приурочены к се-

верным и западным склонам можжевелово-фисташковых редколесий с жасмином в подлеске и моховым покровом. Эта группа имеет большое распространение и характеризуется достаточно высокой сомкнутостью крон (0,7-0,8). Можжевельник достигает в этих группировках высоты 5-6 м.

Эти почвы развиваются преимущественно на карбонатных суглинках, часто на галечниках и пролювиальных отложениях. Влияние почвообразующих пород отражается на гранулометрическом составе этих почв: на делювии глинистых пород развиваются тяжелосуглинистые, а на переотложенных породах средне- и легкосуглинистые их разновидности.

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Морфологически горно-лесные коричневые типичные почвы характеризуются наличием подстилки, темно-коричневой или коричневой окраской верхнего гумусового горизонта с ореховато-комковатой структурой, оглинением среднего слоя почвенного профиля, наличием хорошо выраженного карбонатноиллювиального горизонта в нижней части почвенного профиля.

По гранулометрическому составу данные почвы, в основном, среднесуглинистые, в нижних горизонтах тяжелосуглинистые и легкоглинистые, на долю физической глины в слое 0-100 см приходится 37,70-65,16%.

Горно-лесные коричневые типичные почвы наиболее высокогумусные по сравнению с другими подтипами. В верхнем горизонте гумуса содержится 2,6- 5,8%, вниз по профилю его содержание резко снижается и на глубине 0-100 см падает до 0,9-1,2%. Содержание азота колеблется в верхнем слое в пределах от 0,20 до 0,38%. Реакция почвенного раствора по всему профилю слабо щелочная или щелочная (7,5-8,1), причем повышается с глубиной, что связано с карбонатностью пород. Данные почвы насыщены основаниями: в верхних горизонтах сумма поглощенных оснований составляет 23,53-39,45 мг-экв/100 г почвы.

Горно-лесные коричневые карбонатные почвы по своим морфологическим признакам схожи с типичными, но отличаются характером распределения карбонатов: у них они распределены по всему профилю, начиная с поверхности, а у типичных – с некоторой глубины. Такая карбонатность связана как с засушливостью климата, так и с разреженностью растительного покрова и рельефными условиями.

По гранулометрическому составу эти почвы средне-, тяжелосуглинистые и легкоглинистые: содержание физической глины по профилю 34,16-69,51%. Гумуса в них содержится несколько меньше, чем в типичных: в верхних горизонтах его количество составляет 2,1-4,5%. Содержание азота в верхних горизонтах колеблется в пределах 0,16-0,30%.

Реакция почвенного раствора в горно-лесных коричневых карбонатных почвах по всему профилю щелочная, в нижних горизонтах доходит до 8,4. Сумма поглощенных оснований в верхних горизонтах 19,21-31,10, а в слое 0-50 см 17-95- 26,78 мг-экв/100 г почвы.

Горно-лесные коричневые остепненные почвы распространены на значи-

тельной площади, в основном, на отдельных опушках леса и по окраинным частям аридных редколесий. Выше эти почвы граничат с коричневыми карбонатными почвами аридных редколесий, а ниже с горно-серо-коричневыми почвами. В почвенных исследованиях академика Гасана Алиева территории Большого Кавказа показано остепнение большей части лесных почв. Там, где остепнение началось недавно, такие почвы имеют переходный характер и сохраняют лесные признаки. Можно сказать, что остепнение лесных почв происходит вследствие смены общего фона природных факторов, особенно растительности, при изменении гидротермического режима почв и смене почвообразовательного процесса. После такого изменения типичные лесные почвы постепенно начинают проградировать, и в зависимости от конкретных физико-географических и биоклиматических условий почвообразовательный процесс идет по степному типу. Повышается количество температуры, поступающей в почву, и испарение с поверхности почвы. Также в зоне аридных редколесий имеют значение и другие факторы, как систематическая вырубка леса и выпас скота.

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По результатам проведенных анализов, содержание гумуса в верхних горизонтах горно-лесных коричневых остепненных почв составляет 1,8-4,0%. Количество азота колеблется в слое 0-20 см от 0,15 до 0,29%. Основаниями данные почвы насыщены средне: сумма поглощенных оснований в верхнем слое составляет 17,60-31,45 мг-экв/100 г почвы. Реакция среды в горизонте 0-20 см 7,6-8,2, в слое 0-100 см увеличивается до 8,1-8,4. По гранулометрическому составу данные почвы преимущественно тяжелосуглинистые и глинистые, количество физической глины по профилю составляет 45,55-70,62%.

Аридное редколесье является одним из наиболее приспособленных к аридному климату и эрозионным формам рельефа растительным сообществом. Однако за последнее время условия местообитания их ухудшились. Это связано как с природными факторами (еще большей аридизацией климата, понижением русел горных рек и связанное с этим понижение уровня грунтовых вод), так и с антропогенными (рубка и выпас скота, усиливающие эрозию). Все это привело к тому, что бывший широкий ареал аридных редколесий сильно сократился. Для сохранения имеющихся массивов аридного редколесья и почв, на которых они располагаются, необходимо усилить охрану его участков, запретить выпас скота, содействовать естественному возобновлению основных лесообразующих пород либо высаживать подходящие к данным эколого-почвенным условиям породы.

Литература

1.Алиев Г.А. Почвы Большого Кавказа. Ч.II. Баку: Элм. 1994. 310 с.

2.Алиев Г.А., Халилов С.Г., Абдуева Р.М. Экологические особенности почв аридных редколесий предгорий Большого Кавказа. Баку: ОЗАН, 2001.216 с.

3.Волобуев В.Р. О почвах аридного редколесья Карабахской степи // Труды Института почвоведения и агрохимии АН Аз.ССР. Баку. т.V. 1951. c.3-10.

4.Глазовская М.А. Материалы для классификации почв северных склонов Заилийского Алатау // Изв. АН Казах. ССР. Сер. почв,.1947. №3. Алма-Ата. с.17-42.

5.Литвинская С.А. Охрана редкого гено- и ценофонда Северо-Западного Кавказа. Ростов-на-Дону. Изд-во РГУ. 1993. 110 с.

6.Ройченко Г.И. Почвы южной Киргизии. Фрунзе: Изд АН Киргиз.ССР. 1960.

233 с.

7.Урушадзе Т.Ф., Мхеидзе Е.А. Почвы аридных редколесий Грузии // Почвове-

дение.1971. №6. с.11-22.

8.Холина Т.А. Экологическая характеристика и оценка почв аридных редколесий Турианчайского Государственного заповедника //Известия аграрной науки. Т.7, № 2.

Тбилиси. 2009. с.49-52.

UDC 631.4

Coşkun Gülser, Rıdvan Kızılkaya

Ondokuz Mayıs University, Faculty of Agriculture,

Department of Soil Science & Plant Nutrition, Samsun, Turkey

CONCEPT OF SOIL QUALITY

Abstract. A thin layer of topsoil, takes hundreds of years to form, covers much of the earth as the interface between aquatic, atmospheric, and terrestrial ecosystems. Soil is a fundamental natural resource for basic human needs. Soil can provide the physical support, nutrients, water, and gas exchange necessary for crop growth. Soil is also home to many macro or micro organismswhich directly or indirectly impact crop growth. Soil also supports natural ecosystems

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as it cycles water and chemical elements through the biosphere. Physical, chemical, and biological soil factors determine the need for various inputs, such as water, fertilizer, and pesticides. The health of our environment depends on soil, air, and water quality. Therefore, soil management will always be important.

Evaluating soil quality is not the same classifying soils based on their natural properties. Soil quality is not concerned with rating or comparing the suitability of different soil types for a specific use. Soil quality is an evaluation of the condition of a particular soil in relation to its potential capacity. Therefore, the focus of soil quality is on properties or processes impacted by soil use or management. The importance of soil quality and how it may be defined, evaluated, and managed will be discussed during this workshop.

Key words: topsoil, soil quality, soil formation, destruction, clay transformation pseudo gleying, erosion, salinization, soil fertility, soil porosity, soil aggregate stability

Definition of Soil Quality. The soil quality concept placed in the literature in the early 1990s [13, 45]. Soil quality is usually defined as ‗‗the capacity of a specific kind of soil to function, within natural or managed ecosystem boundaries, to sustain plant and animal productivity, maintain or enhance water and air quality, and support human health and habitation‘‘ [25]. This definition is similar to that of Doran et al.

(1996) in which soil quality is the "capacity of a soil to function, within ecosystem and land-use boundaries, to sustain biological productivity, maintain environmental quality, and promote plant, animal and human health". These functions of soils in many soil quality definitions include a soil‘s role in plant growth, hydrology, biological transformations, and degradation of organic materials. According to these definitions, soil quality has two parts: an intrinsic part covering a soil's inherent capacity for crop growth, and a dynamic part influenced by the manager. A good quality soils can be degraded by poor management. Dynamic part of soil quality generally changes in response to soil use and management [32]. The distinction between inherent and dynamic parts of soil quality can be characterized by the genetic (or static) pedological processes versus the kinetic (or dynamic) processes in soil [37, 29, 8].

Attributes of natural or inherent soil quality which is a function of geological materials and soil state factors or variables such as topography, parent material, mineralogy and particle size distribution, are mainly viewed as almost static and usually show little change over time. Some soils have poor inherent quality and are not fit or suitable for a specific use or crop production. On the other hand, human activities such as land use and farming practices can result in the deterioration of a soil that originally possessed good inherent quality due to adverse management and/or climatic effects such as; soil erosion and desertification (Table 1).

Soil properties related with dynamic soil quality can change in response to human use and management over relatively short time periods (Table 2). Total organic matter may change over a period of years to decades, whereas pH and labile organic matter fractions may change over a period of months to years. On the other hand, microbial biomass and populations, soil respiration, nutrient mineralization rates, and macroporosity can change over a period of hours to days. Therefore, maintenance and/or improvement of dynamic soil quality deals primarily with those attributes or indicators that are most subject to change (e.g., loss or depletion) and are strongly influenced by soil management or agronomic practices [9].

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Loosening

Desalinization

Attributes of Soil Quality Indicators. The sustainability and productivity of land use can be affected by the quality of soil which is controlled by chemical, physical, and biological components of a soil and their interactions [36]. Soil physical and chemical properties are shaped by biological activity, and biological activity is enhanced or limited by chemical and physical soil conditions. Therefore, specifically categorizing some soil indicators is difficult. For example, cation exchange capacity could be classified as either a physical or a chemical property, and organic matter as either and most useful indicators of soil quality integrate the combined effects of several properties or processes.

Karlen et al. (1997) reported that soil quality affects basic soil functions, such as moderating and partitioning water and solute movement, their redistribution and supply to plants; storing and cycling nutrients; filtering, buffering, immobilizing and detoxifying organic and inorganic materials; promoting root growth; providing resistance to erosion. The capacity of soil to function can be reflected by measured soil physical, chemical and biological properties, also known as soil quality indicators (Table 3). There are

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several criteria in selection of soil quality indicators. Generally, appropriate soil quality indicators should be:

-easy to asses.

-able to measure changes in soil function both at plot and landscape scales.

-assessed in time to make management decisions.

-accessible to many farmers.

-sensitive to variations in agro-ecological zone.

-representative of physical, biological or chemical properties of soil.

-assessed by both qualitative and/or quantitative approaches.

Physical Soil Quality Indicators. Physical indicators of soil quality are mostly related to water storage and movement, soil structure. Basic physical indicators of soil quality are soil texture, soil depth, infiltration, bulk density, water holding capacity, aggregate stability and penetration resistance (Table 4). Some physical indicators such as; texture and topsoil depth are fixed soil properties that cannot be altered, except over long time periods or sediment deposition by erosion. These soil properties influence soil use or productivity, they are inherent part of soil quality. For example, soil texture is an inherent soil property which strongly influences many soil quality indicators, like drainage and water holding capacity.

Infiltration is the process of water entering the soil from boundry of soil atmosphere system. The infiltration rate is dependent on the soil type; soil structure, or amount of aggregation; and the soil water content. The infiltration rate is usually higher when the soil is dry than when it is wet. Therefore the soils should have similar moisture content when taking the measurements for soil quality assesment.

Bulk density is dependent on the densities of the soil particles (sand, silt, clay, and organic matter) and their packing arrangement. Bulk density is a dynamic property that varies with the structural condition of the soil. This condition can be altered by cultivation; trampling by animals; agricultural machinery; and climate (raindrop impact etc). Compacted soil layers have high bulk densities, restrict root growth, and inhibit the movement of air and water through the soil.

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Soil structure is the combination and spatial arrangement of primary soil particles into larger secondary particles known as aggregates, peds, clods, etc. An aggregated structure is generally considered best for agricultural activities. A good soil structure is defined as an arrangement of soil particles into stable larger units, and of the pore spaces between those units, that allows movement of water through the soil, movement of air into and out of the soil and ease of penetration by roots, and that protects the soil against erosion [19]. Pore size distribution is considered to be a good indicator of the soil structural condition and useful for predicting water infiltration rates, water availability to plants, soil water storage capacity, and soil aeration status [9]. Aggregate stability is a measure of the vulnerability of soil aggregates to external destructive forces [22]. In general, the greater the percentage of stable aggregates, the less erodible the soil will be. Soil aggregates are a product of the soil microbial community, the soil organic and mineral components, the nature of the above-ground plant community, and ecosystem history. They are important in the movement and storage of soil water and in soil aeration, erosion, root development, and microbial community activity [42]. Aggregates improve soil quality by protecting soil organic matter entrapped in the aggregates from exposure to air and microbial decomposition, decreasing soil erodibility, improving water and air movement, improving the physical environment for root growth and improving soil organism habitat [44]. Breakdown of aggregates is the first step to crust development and surface sealing, which impedes water infiltration and increases erosion. Soil aggregation can change over a period of time, such as in a season or year. Aggregates can form, disintegrate, and reform periodically [22].

Penetration measurements have been used to study tillage effects on penetration resistance [21, 20] and to estimate soil trafficability and soil resistance to plowing, seedling emergence and root growth [21, 3]. Penetration resistance provides an indicator of when soil strength becomes too great for effective penetration by crop roots. Extensive work has shown that for most agricultural crops root growth slows dramatically when the penetration resistance exceeds about 1.7 or 2 MPa [4, 6, 2].

Chemical Soil Quality Indicators. Chemical indicators of soil quality are mostly related to nutrient availability, phytotoxicity of trace metals, and pesticide mobility in soils. Basic chemical indicators of soil quality are soil organic matter (SOM), soil reaction (pH), electrical conductivity (EC), NO3--N, cation exchange capacity (CEC) (Table 4). Soil organic matter, which is one of the most important factors affecting soil quality, is a soil component having physical, chemical, and biological properties. Types of organic matter are very difficult to describe. Soil organic matter is generally described as one of three types which are i) living organisms including plant roots, ii) readily turned over or decomposed under favorable conditions which is active part of SOM (in periods often measured in months) and iii) humus, which is relatively stable and resistant to further decomposition(often lasting hundreds of years). Composition of soil organic matter defined by different researchers is given in Table 5.

Decomposition of ―active‖ organic residues produces long polysaccharides which are bind soil particles into stable aggregates that resist compaction and erosion. Tisdall and Oades (1982) concluded that only a part of the SOM stabilizes aggregates: generally the younger SOM with a larger content of polysaccharides, roots and fungal hyphae. Aggregation is also promoted by the binding action of plant roots, and root exudates. Aggregation and the activity of earthworms, burrowing insects, and plant roots

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create channels that aid water infiltration, aeration, and drainage. Organic matter increases soil water-holding capacity in coarse textures soils. Assimilation by living plants and soil organisms retains nutrients, preventing them from leaching. Decomposition of SOM releases nutrients essential for the growth of plants and soil organisms. Humus, which is stable part of SOM, buffers soil pH and retains nutrients through its contribution to CEC. SOM provides food and energy for soil organisms.

pH of soil solutions influences on element solubility in soils. The processes of mineral dissolution and also adsorption at acidic functional groups are dependent on pH. Cation exchange capacity also depends on pH. Nutrient deficiencies of the base nutrient cations Ca, Mg, and K, and also P deficiency are mostly associated with lower soil pH or acidic soils. Trace elements such as; Fe, Mn, Zn, Cu and Al cause toxicity to plants in acidic soils. Alkaline soils are associated with deficiencies of trace elements and also deficiencies of P [33].

Eventhough EC is generally related to salinity, it is also reflects dissolved nutrients in anion and cation forms in soils [41], and is an important parameter for monitoring organic matter mineralization in soils [10]. Salinity limits crop production when the concentration of soluble salts in the soil solution is high enough to decrease absorption of water. The critical EC at which growth is affected depends on plant species [5]. High ratio of exchangeable Na can cause swelling of soil aggregates and clay dispersion, which results in a decrease in permeability [38].

Soil nitrate (NO3-) is a form of inorganic N that is available for use by plants. It forms from the mineralization of organic forms of N in the soil by microorganisms. The rate of N mineralization is dependent on the amount of soil organic N, water content, temperature, pH, and aeration. Crop needs are met by mineralized-N and by fertilizer-N. Nitrate is the most mobile form of N in soil, so it can be leached with percolating water below the root zone. Nitrate is not a contaminant until it leaches below the root zone or is transported off-site in surface runoff [44]. Nitrate can contribute to euthrophication when leached to groundwater.

Exchangeable cations are cations that are adsorbed weakly by soil particles and can be easily displaced from the soil particle surface into the solution phase by another cation. The cation exchange capacity is the net negative charge of a given weight of soil. CEC is especially important for the essential plant nutrients K, Ca, and Mg. These nutrients are protected from leaching when held in exchangeable form on particle surfaces. These are a reserve nutrient supply that can replenish ions taken up by plant roots.

Biological Soil Quality Indicators . Biological indicators of soil quality often refer to the amounts, types, and activities of soil organisms. Basic biological indicators of soil quality are microbial biomass C and N, soil respiration, enzymes and earthworms

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(Table 4). The microbial biomass can quickly respond to changes in soil processes resulting from changes in management due to its high turnover rate relative to the total soil organic matter. The microbial biomass C can be divided by total organic C or CO2- C respired in order to make comparisons between soils under different managements having different organic matter contents. The ratio of microbial biomass C to total organic C has been useful to explain changes in organic matter under different cropping or tillage systems, as well as in soil polluted by heavy metals [18]. Carbon mineralization is the gross flux of CO2 from soil during an incubation and indicates the total metabolic activity of heterotrophic soil organisms. Nitrogen mineralization is the net flux of inorganic N during a soil incubation and represents the balance between gross mineralization and immobilization by soil organisms [18].

Soil respiration is the rate of CO2 release (or oxygen consumption) by biological respiration. Soil respiration rate represents the size and activity of the overall population of soil organisms. Soil microbes generally make the largest contribution to soil respiration, although field measurements can include significant contributions from larger organisms and plant roots. Soil temperature, moisture, aeration, and food supply all have major effects on biological activity, and therefore respiration rate [44].

Enzymes catalyse innumerable reactions in soils and are associated with organic matter decomposition and nutrient recycling. They exist in soil in a biotic form associated with viable microorganisms or soil fauna. Enzymes are important in facilitating the hydrolysis of substrates that are too insoluble or too large for microorganisms to use directly [18].

Earthworms improve soil quality by increasing the availability of nutrients. Available plant nutrients (N, P, & K) tend to be higher in fresh earthworm casts than in the bulk soil. Earthworms also accelerate the decomposition of organic matter by incorporating litter into the soil and activating both mineralization and humification processes; improve soil physical properties, such as aggregation and soil porosity; suppress certain pests or disease organisms; and enhance beneficial microorganisms [17].

Evaluating Soil Quality. Soil quality is evaluated using indicators that measure specific physical, chemical, and biological soil properties. The smallest set of properties or attributes that can be used to characterize an aspect of soil quality is called as minimum data set. Indicators in minimum data set of soil quality are need to be developed for (i) integrate soil physical, chemical and/or biological properties and processes, (ii) apply under diverse field conditions, (iii) complement either existing databases or easily measurable data, and (iv) respond to land use, management practices, climate and human factors (Doran and Parkin, 1994). Monitoring changes in the key soil quality indicators with time can determine if quality of a soil under a given land use and management system is improving, stable or declining [30, 40].

Loveland and Webb (2003) reported that a major threshold for soil OC is 2% (3.45% SOM), below which potentially serious decline in soil quality will occur. Shukla et al. (2006) determined the dominant factors in assessing soil quality. Soil aeration was the most discriminating factor for the 0–10 cm depth and soil aggregation was the most significant factor for the 10–20 cm depth of soil. For each factor, the dominant measured soil attribute was soil organic carbon. They concluded that if only one soil attribute were to be used for monitoring soil quality changes every 3–5 years, soil organic carbon should be selected. Clay concentration and SOM influence aggregation which effect wa-

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