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Section 1. Biology
Abdurakhmonov Nodirjon Yulchievich, PhD., Senior researcher Research institute of Soil science and Agrochemistry E-mail: nodirjon_1976@mail.ru Kuziev Ramazon, DSc, (Doctor of science in Biology), professor Research institute of Soil science and Agrochemistry E-mail: kuziev_gosniipa@mail.ru
OASIS SOILS OF UZBEKISTAN
Abstract: In the article materials on comparative analysis of different characteristics of natural and irrigated soils are given. A fertility of soils is related to its forming processes and changes according to soil evolution and development.
Keywords: soil type, automorphic, hydromorphic, serozem soils, oasis soils, salinity, carbonates, humus.
Introduction
Among agricultural sectors, irrigated agriculture has ancient history and originated in Egypt, China, and Central Asia few thousand years ago. Theoretical deep analysis and reasoning of the issues of the change of natural soils under irrigated agriculture, evolution and formation of the fertility began at the end of the nineteenth century.
Changes of natural soils under the influence of irrigated agriculture occur in three main areas:
1) under the effect of irrigation water soil wetting increases which lead to development of elyuvial processes;
2) transport of a variety of solid and dissolved substances in irrigation water results formation of new agroirrigation horizon;
3) accumulation biologically active elements in the soil and increase of biological activity under the influence of the cultivation of crops and the effects of various agricultural technical activities.
As a result, in dry and very dry regions of Central Asia, from natural soils of this region completely different new cultural oasis soils will form. Formation, development, evolution, fertility problems of oasis soil have a great importance in soil science. Because, rationale the theoretical
aspects ofthese issues, and the effective use of irrigated soils without damage to the environmen is very important.
Object and methods of the research.Tashkent and Samarkand oases were selected as the main object ofthe detailed studies, which has quite different natural conditions and age ofanthropogenic soil formation. Currently, these oases are major regions ofirrigated agriculture in the Republic.
In addition, in order to reveal the regularities of oasis soil formation, refinement of nomenclature and classification of irrigated soils, route studies of the soils of other oases of the republic, including Ferghana, Bukhara, Khorezm and others were conducted.
The methods of field, laboratory and cameral study of soils were used, including:
- comparative-geographical, genetic, comparative-historical methods of soil investigation;
- compilation of soil maps of different scale (M: 1: 10000, M: 1: 25000; M: 1: 100000, etc.);
- long-term studies of the productive capacity of soils in key areas and in lysimeters;
- study of morphological features, chemical, physical and other properties of soils in field and laboratory conditions.
Results of the research. In oases of Central Asia, including in Uzbekistan, in contrast to the natural soils under the effect of irrigation will create a new oasis soils. If in the humid countries (such as in the black soil zone), irrigation is only supplement to natural rainfall, in Uzbekistan the water supplied to the plant is higher more than a few times in comparison to average annual precipitation. The main difference according to A. A. Rode [8; 9] that several humidification of the soil and lower layers of the soil during the growing season. Our observations on serozem soils of Tashkent and Samarkand oases shows that soil, as a result of irrigation especially of excessive irrigation soil layer will not only moisten, but water completely washes soil and under soil layers reaches to the groundwater; therefore, there is unique elementary soil forming process.
In addition, if the climate of the oases is a little different from the climate of surrounding natural landscape, microclimate of vegetation fields significantly different from them. The humidity, the temperature of the earth and above height of 2 meters has 25-35% difference.
Central Asia, including Uzbekistan rivers' water is characterized by turbidity in different level. The reason of the turbidity is transport and erosion of small particles in stream and river formation areas. For example, in the mountainous part Zarafshan River transfers 500-1000 tons of small particles from the 1 km2. The chemical composition of these particles associated with the river basin soils and varies throughout the year in the different parts of the river. These particles under the influence of irrigation water flow are transported to the fields. According to V. A. Molodtsov [4], R. K. Kuziyev [3], 22.6-40.0% of solid particles remain in irrigated ditch not reaching to fields. The rest bring 10,8-17,9 tons of solid particles to fields. This is 0,8-1,3 mm thick layer on the ground. Thus, in 250-300 years 30 cm of new layer can be appear. The quality of the new layer depends on the quality of irrigated layers.
Human tries to change lands according to the activities related to it. One of the most common elements of farming on irrigated lands, in the absence of fertilizers these particles extracted and laid to the grounds as fertilizer. As mentioned in S. K. Kondratev (1916), 280 tons of solid particles applied for one hectare from irrigated ditch. These activities drastically change the process of formation and development of soil in oases.
Thus, many ages of irrigated agriculture old has affected for the creation of oasis soils in Central Asia, including oasis soils of our Republic, which is different from natural soil. At the same time, it is obvious that these soils are originated from natural soils which found before irrigated agriculture began. Irrigated soils' formation, structure, properties, intensity of the evolution and productivity issues have been studied by many researchers such as, M. A. Orlov, 1937; A. N. Rozanov, 1946; S. N. Ryjov, 1958; B. A. Gorbunov, 1965; N. V. Kimberg, 1974; R. K. Kuziyev, 1991; 1994; 2011; 2014; R. K. Kuziyev and N.Yu.Abduraxmonov, 2015.
Oasis soils are formed under the influence of human activities, and level to a certain extent natural soil formation process in various conditions. Among soil scientists first M. A. Orlov mentioned this [6], and recommended the term "irrigated cultural" soil. Later, this work is implemented to land distribution and classification by Uzbek soil scientists B. V. Gorbunov, N. V. Kimberg, S. A. Shuvalov, S. P. Suchkov. On the basis of these works these soils differentiated from serozem soils zone which occupies foothills planes of the desert zone, the differences are reasoned. However, the irrigated soils are not differentiated as an independent soil type.
The independent soil type - is a large group of soils, and it develops in same climate, biological, lithological, hydro-geological conditions and soil formation process is characterized by a vivid manifestation.
Integrity and properties of soil type are determined by the following: uniformity of transport of organic residues in the soil and processes of their decomposition and humus formation; uniformity of decomposition of mineral mass and a synthesis of new complexes organic-mineral compounds; same type of migration (movement) and accumulation (store) of substances; same type of soil profile structure and character of a genetic horizons; same direction of measures aimed at improving and conserving of fertility of the soil.
A comparative description of the specifics of different characteristics and properties of natural and irrigated soils shows that the soil forming processes are significantly different in these soils.
First of all, it should be noted that in dry and very dry regions during the irrigation of lands several times a lot of moisture falls to soil compared to atmospheric precipitation. As a result, as the above mentioned, new
type of soil-water regime - irrigation water regime type will occur. The main difference of this is humidification of soil top layers, in some cases to groundwater level a lot of times, during the growing season.
Change of humidification regime in soils in the irrigation process accelerates eluvial processes. As a result, automorphic soil of oases, which in secondary salinity not occur, for example, in serozem-oasis soils amount of chloride and sulphate salts of calcium, magnesium and sodium are reduce.
The soils of Tashkent and Samarqand oases are not salinized by water-soluble salts and has almost no significant effect on the fertility of the soil. In typical serozem soil zones, water-soluble salts in soil profile are completely washed away during the first vegetation period. In the early period of irrigation, water-soluble salts washed to the lower horizontal and then as this process continues and
In natural serozem soils, as researchers have pointed out many times, the amount of humus is not high. But in some of the horizons the amount of humus is lower. For example, in grass layers of typical serozems, humus content can be 4.0 percent. In dark serozem soils this can be 5,0-6,0%. As we reflect about humus of natural soils, we should note that, firstly, the amount of humus increases from light to dark serozem soils. Second, the amount of humus declines sharply from grass layers to under. Beginning from the second meter, the amount of humus, in many cases, is close to
salts are removed from the soils [1]. A small amount of water-soluble salts can be observed at a depth of 3-5 meters oftypical serozem soils. Water-soluble salts, including gypsum accumulation can be observed in some cases at a depth of 2 meter, but the amount is not much.
The level of distribution of carbonates in soil profile changes sharply in the irrigation process. During the start of the process of irrigation a specific amount of carbonates and their typical distribution in the profile of natural soils in irrigated light, typical and dark serozem soils remain for a few years. But, especially in the serozem-oasis soils, this process is completely changed, carbonate profile only specific to this subtype is occur (Table 1). Serozem-oasis soils formed from agroirrigation transport substances, the amount of carbonates will be considerably less. In addition, the role of carbonates in the profile also have a big difference from natural soils [2; 10].
the amount of humus in the parent rock-lyoss, consists 0,10-0,20%.
In particular, during formation of serozem-oasis soils, formation of humus, its distribution in the profile differs sharply from the reserve soils and new humus formation process will occur. During the process of irrigation, soil humus reserve increases. When compared reserves of humus in soils formed in different regions, the amount of humus, first of all, association with the conditions of soil formation (in automorphic or hydro-morphic) is observed clearly (Figure 1).
Table 1. - Content and composition of serozem-oasis soil, in%
Layer Layer depth, cm Carbonates Layer Layer depth, cm Carbonates
^2 Са Mg ^2 Са Mg
Serozem-oasis soils Irrigated serozem soils
60-84 0-10 5.89 5.1 0.36 130-85 0-10 9.8 7.0 0.30
10-30 5.98 5.2 0.48 10-29 10.26 7.4 0.18
30-40 6.55 5.8 0.36 29-43 10.18 8.1 0.24
40-58 7.21 6.3 0.48 43-60 11.18 8.1 0.36
58-100 8.05 7.3 0.36 60-85 11.18 8.1 0.36
100-125 7.43 6.4 0.48 85-115 11.12 7.9 0.42
125-170 7.65 7.0 0.48 115-150 10.80 7.7 0.48
170-200 8.27 7.4 0.48 150-200 10.15 7.4 0.36
200-250 9.76 7.8 0.48 200-250 10.26 7.3 0.36
Figure 2. Dependence of the reserve of soil humus to irrigation period
The soil forming process in oases is characterized by specific transport of organic substances to soil, decomposition and synthesis of humus-complex organic substance. In the process of development and irrigation of the soils, plant cover character and the formation of and humus significantly change. The biological productivity of oasis-serozem soils is higher compared to reserve serozem soils. For example, in the cotton fields, biomass of plants on the land can be 10-15 per hectare, biomass of roots 25 tonnes. This is followed by decomposition of them, the formation of a certain level of soil fertility. Of course, the humus consumption significantly increases because of the irrigation process. As a result, the process of formation of humus is more active in irrigated soils. The humus formation process, in oasis soils compared to natural soils is characterized by different in terms of the quality and quantity of biomass and its mineralization. This in turn is reflected in the formation of humus profiles.
When compared the amount of humus in oasis au-tomorphic and hydromorphic soils, in hydromorphic conditions more active humus accumulation process is observed. The calculation of humus reserve in soil profile allow to discover some general laws. In serozem-oasis automorphic soils during early irrigation, depletion of humus reserves, then the increase of them can be observed. In particular, reserves of soil humus in oasis soils
significantly higher than the natural soil. In hydromor-phic oasis soils in the process of irrigation the soil humus reserves are decreased and their amount stabilized in meadow-oasis soils. Thus, the process of oasis soil formation makes closer each other conditions specific to independent natural soil types.
Conclusion
1. Oasis of Uzbekistan is one of the few regions of the Earth where, as a result of irrigation, powerful anthropogenic soils have formed that have blocked natural soil formations in newly created cultural landscapes. At the same time, the culturally anthropogenic process superimposed on the natural processes of soil formation does not lead to an absolute leveling of the latter, as a result of which series of special soil types are formed in the oases: serozem - oasis, meadow - oasis, desert - oasis and others.
2. In serozem - oasis soils, migration processes of readily soluble salts, gypsum and carbonates are intensified. In a complex process of oasis soil formation, two opposite phenomena of carbonate migration collide: their biological accumulation and illuviation. The latter prevails. This is most clearly expressed in serozem-oasis soils, where the difference in carbonate content between soil horizons and subsoil is 5-7%. In irrigated serozem, the difference in carbonate content is about 3%. With a high content of carbonates, this decrease is hardly notice-
able, but plays a certain negative role in the fertility of oasis soils, since the most active, mobile calcium compounds are carried out first.
3. The humus content of irrigated soils does not have a correlative dependence on the original soils and is es-
tablished at a new level determined by the zonal position and the level of the crop irrigation culture. In the process of oasis soil formation, the level of humus in all types of irrigated soils is, to a certain degree, leveled and approaches the average for this zone.
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