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Gafurova Lazizakhon Akramovna, professor, Department of Soil science, National University of Uzbekistan E-mail: [email protected] Kadirova Dilrabo Abdukarimovna, associate professor, Department of Agrochemistry and Soil science, Tashkent state agrarian University E-mail: [email protected],
COMPLEX GENETIC RESEARCH OF SOILS OF SURKHANDARYA VALLEY WITH MICROBIOLOGICAL AND BIOCHEMICAL STUDY
Abstract: The article provides the results of the analysis of morphogenetic features, agrochemical and agrophysi-cal properties of soils of the study area and influence of degradation processes. Also, analyzed the materials obtained on the basis of a complex system of biological studies on the number of some of physiological groups of soil microorganisms, the activity of redox and hydrolytic enzymes and the release rate of carbon dioxide emissions in the studied soils depending on the change of soil vertical and horizontal zonation, and degree of erosion and salinity, as well as seasons of the year. The studies revealed a correlation between the biological activity and the main indicators of soil fertility, the coefficient of humification and the total gross BA relative indicator for each soil type and subtype.
Keywords: mountain and foothill soils, irrigated soils, desert soils, erosion, salinity, degree erosion and salinity, number of microorganisms activity enzymes.
Introduction
Modern problems of effective land use and an increase in their fertility pose new practical tasks in soil science, which require in-depth theoretical studies for their solution using biological methods. With biological methods of soil study, one can obtain a general idea of the agronomic quality of soil [2, 3]. So, it can be considered that a comprehensive genetic study of soils with the use of morphogenetic, agrophysical, agrochemical, microbiological and biochemical research is relevant in developing scientific and theoretical bases for increasing the fertility of eroded and saline soils.
As is known, erosion and salinization of soils are important aspects of degradation, characterized by the destruction and depletion of soil cover under the effect of natural and anthropogenic factors. In the process of erosion and salinization of soils, the integrity of soil cover of landscapes is violated, its physical, chemical and biological properties change. It is known that biological activity is an important indicator of soil fertility [4, 5]. One of the components ofbiological activity of soil is a composition and abundance of microflora, enzymatic activity. The state of soil biota and the activity of enzymes affect the fertility of soil, circulation rate of chemical elements falling into soil as the products of vital activity of plants and animals, from the bedrock lying under soil layer. The integral index of biological activity of soils - the intensity of release of gaseous metabolite, carbon dioxide, characterizing soil "breathing", is the most important element of ecological soil
monitoring and together with classical morphological method and results of chemical analysis of soils it allows a comprehensive assessment of the state of soil [6].
Object and methods of research. The objects of the study are soils, distributed in the conditions of vertical and horizontal zonality of the Surkhandarya Valley. The studies are carried out with the following types of soil: eroded rain-fed dark serozems formed on loess and tertiary red-colored sediments, mountain-brown carbonate and mountain-brown typical; old-irrigated meadow, old-irrigated marsh-meadow, irrigated meadow, freshly reclaimed marsh-meadow and irrigated typical serozems, old-irrigated light serozems, irrigated meadow-serozem and freshly irrigated typical soils of the sero-zem belt, as well as saline irrigated takyr-like - meadow, irrigated meadow desert-sand, old-irrigated meadow, old irrigated takyr-like meadow, freshly-irrigated meadow, old-irrigated meadow-takyr-like, freshly-reclaimed desert meadow soils.
Soil analysis is performed according to generally accepted methods, the methods developed in UzNIIKH (1977) and the Manual on chemical soil analysis, by Arinushkina [1]. The main agronomically important physiological groups of microorganisms are determined according to the generally accepted methods of the Institute of Microbiology of the Academy of Sciences of Uzbekistan. Soil breath is assessed according to the Shtatnov method in the Koleshko modification. The activity of soil enzymes is determined by the methods of soil enzymology described by F. Kh. Khaziev [7].
COMPLEX GENETIC RESEARCH OF SOILS OF SURKHANDARYA VALLEY WITH MICROBIOLOGICAL AND BIOCHEMICAL STUDY
Analysis of agrochemical and agrophysical properties of soils is carried out with spring samples; the study of microbiological and enzymatic activity of soils is carried out in spring, summer, and autumn.
Results of research. The Surkhandarya valley is an area of extremely southern location in Uzbekistan; it includes all basic types of landscape inherent Uzbekistan - from desert plains to mountain zone. The area under consideration is characterized on the one hand by the complexity of geological structure, the formation of relief, on the other hand by a variety of soils, peculiar soil-forming rocks, a variety of hydrothermal, climatic conditions (especially arid ones), that result in development of a sparse vegetation and low biogenic character of soils; all that give rise to degradation processes (such as erosion, salinization, etc.).
In connection with the degradation processes in morphological features of mountain-brown soils in the Surkhandarya region, the increase in thickness of the humus horizon is observed, as well as the decrease in thickness of the transition horizon, the presence of darker tones, the predominance of waterproof and nutty structure, more marked manifestation of clayey horizon, more deep occurrence of carbonate horizon. Irrigated soils are distinguished by the presence of an agroirrigation horizon. In desert soils, due to extreme dynamism of the regime of moistening and salinization of soils, a certain imprint is imposed in the structure of soil profile, which is the reason of its heterogeneity observed throughout the lithologi-cal structure.
The studied soils, depending on different formation conditions, are not the same in mechanical composition; this is related to the genesis of soils, the processes of erosion and salinity. Washed out soils are characterized by less porosity than non-washed and washed over soils, it helps to limit the activity of enzymes and microorganisms.
Characteristic feature of the investigated desert soils is stratification and sharp change in mechanical composition along the soil profile. In some places clay loams are interbed-ded with sandy loam, and sand soil - with clays; sharp fluctuation in the content of mechanical fractions is associated with sharp and more contrasting change in lithology of alluvial deposits.
The intensity of the processes of erosion and salinity depends on the soil-ecological conditions of the region, which is reflected in the agrochemical properties of soil. According to humus and nutrients content in studied soils the following decreasing sequence could be built: mountain brown typical -mountain-brown carbonate - dark serozem on loess - dark serozem on tertiary - old-irrigated meadow - freshly irrigated typical serozem - irrigated meadow desert-sandy - old-irrigated takyr-like - meadow soils.
Soils of the investigated territory under the influence of degradation processes differ in composition of microbial associations and in intensity of microbiological processes. The main feature of soils of the studied region is their relatively low microbiological activity. The highest activity is observed in mountain-brown typical soils. The largest number of microorganisms is in the upper horizons, and sharp decrease occurs in the lower horizons. The content of microorganisms varies depending on slope exposure, the degree of erosion and salinity. Among the groups of microorganisms studied, ammoni-fiers are the most predominant group in microbial population, the second largest in number are the actinomycetes and fungi, followed by nitrogen-fixing and nitrifying microorganisms. Oily-acid microorganisms are presented in a smaller amount. Decomposition of cellulose in these soils is slow, with the exception of irrigated soils.
The processes of erosion and salinization have a negative effect on the development of the studied groups of microorganisms, and the more pronounced these processes are, the poorer the soils.
The effect of erosion on microbiological activity of soils is more pronounced in mountain and foothill soils, and salinization - in desert soils, the main limiting factor in microorganisms growth in these soils is the lack of food and moisture. Microorganism content in soil also varies with slope exposure, the degree of erosion and salinity, the duration of irrigation, cultivation, the type of agricultural use, and the morphoge-netic structure of soil.
The production of C02 in investigated soils depends on soil-ecological conditions, soil properties, quantitative composition of microflora, etc. The amount of C02 emissions increases from irrigated soils to mountain-brown soils, from soils located in southern exposures to the northern ones, from washed out to non-washed and washed over soils. The degree of salinity has a different effect on the release of carbon dioxide. Strongly saline desert soils are characterized by low intensity of carbon dioxide emissions in comparison with medium and slightly saline soils.
In connection with its special role in soil formation and effects on plant life factors, enzymatic activity is one of the most complex phenomena occurring in soil; it depends on the conditions of soil formation. In the process of degradation, the main soil-ecological parameters that control the enzyme level of soil deteriorate, as a result, the enzymatic activity also decreases. At transition to the mountain-brown soils, the activity of studied oxidation-reduction and hydrolytic enzymes increases with an increase in total microbiological activity, humus and nutrients content, which decrease down the profile. Due to the intensification of soil erosion and salinization processes, the genetic types studied are characterized by a lower
level of enzymatic activity than non-washed, slightly saline and non-saline soils.
The seasonal dynamics of biological activity of soils is determined by the hydrothermal conditions of the region. It has been revealed that in each soil species under study with specific physico-chemical properties, a certain number of microorganisms develops and an equilibrium of biochemical process is established, typical for these conditions and seasons. According to the seasonal dynamics of biological activity of soils studied, they can be classified as a type - with a minimum in summer and a maximum in spring and autumn.
The established correlation dependencies indicate the presence of a connection between biological activity, the parameters under consideration and the basic properties of soils in the desert zone, which allows using them as biological tests to diagnose the fertility of eroded and saline soils.
Complex study of biological of degraded soils with different physicochemical, microbiological and biochemical properties, and heterogeneous structure of soil profile, makes it possible to disclose their ecological and genetic character-
istics, as well as the extent to which natural and ecological factors influence the fertility of soils. Relatively high value of biological activity in studied soils has mountain-brown typical soils, and the least value - moderate saline desert takyr-like meadow soils. The change in biological activity of soil can indicate the change in the level of its fertility; this makes it possible to recommend indicators of general biological activity for widespread use in monitoring and bio-indication of soils.
Conclusions. Thus, a comprehensive study of biological activity of soils in the area under study, including the biota, the products of its life activity, together with the abiotic components, reveals geographical diversity and genetic features of soils, the patterns of their interconnection and interdependence, and the extent to which natural and ecological factors influence the fertility of soils. The refinement of the actual diagnostics of soil fertility by morphogenetic indicators, chemical composition, physical and biological properties, erosion, salinity characteristic in the area under study will contribute to more rational location of crops and implementation of antidegradation measures.
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