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Section 1. Biology
Madrimov Rajabboy Masharipovich, PhD, the Faculty of Biology E-mail: madrimov91@gmail.com Nabieva Gulchekhra Mirergashevna, National University of Uzbekistan, Doctor of Biological Sciences, the Faculty of Biology E-mail: gulchekhra-nabieva@rambler.ru Gafurova Lazizakhon Akramovna, National University of Uzbekistan, Doctor of Biological Sciences, Professor, the Faculty of Biology E-mail: glazizakhon@yandex.ru
CHARACTERISTIC FEATURES OF GUMUS STATE IN GRAY-BROWN SOILS OF THE PITNYAK OASIS IN THE WESTERN PART OF UZBEKISTAN
Abstract: Group and fraction composition of humus of the Pitnyak oasis in the Khorezm region has been studied in the paper. In connection with the irrigation of the Tashsakin plateau soils, a transition of fulvate type of humus in virgin gray-brown soil to humate-fulvate and fulvate-humate types in irrigated gray-brown and gray-brown meadow soils is observed. Long-term irrigation and cultivation of meadow soils of the alluvial-lacustrineriverbed of Daudan have led to the formation of humus of a humate type, formed oftightly bound compounds in the form of calcium humates and organic-mineral substances.
Keywords: oasis, humus, humic and fulvic acids, gray-brown soils.
Introduction. As the most important factor in mic state and humus composition in soils determine the diversity of processes occurring in the mineral the classification of soils, which is very important in part of soil and formation of the soil profile, hu- the compilation of soil maps of different levels. mus to a great extent determines physical, physico- Long-term studies of soils in the desert zone (nat-chemical, biochemical, microbiological properties ural soils and anthropogenically altered, i.e. irrigated and fertility of soils. ones), allow to establish certain regularities in the soil
The content and composition of humus largely formation of gray-brown soils, distributed in vast ar-depends on geographic, zonal and climatic condi- eas of the Ustyurt plateau, Devkhana plateau, the tions of soil formation and anthropogenic activities Malikchul plain, and the Tashsak plateau on which associated with irrigated agriculture. In addition, hu- irrigated agriculture is currently developing [4].
Over the past decades in the Khorezm region, the level of farming has reached a maximum, creating the preconditions for changing soil-melioration conditions. This led to a rise in groundwater level, because of which a redistribution of water-soluble salts, gypsum, carbonates and nutrition elementswas observed. In addition, with the construction of the Tuyamuyun waterworks, the development of adjacent lands occurred, including the Pitnyak oasis.
Objects and methods of research. Actually, the Pitnyak oasis, located in the southeastern part of the Khorezm region, is a district of the Tashsakin plateau, a fragment of the ancient Daudan riverbed, to which the Zaunguz Karakums adjoin in the south and southwest.
On the surface the plateau is covered with strongly calcareous gravelly loams, under which lie loose sands and sandstones with interlayers of pebbles, conglomerates and marly clays of Pliocene age [2]. The area of the ancient Daudan riverbed is composed of alluvial-lacustrine deposits, heterogeneous in tex-ture.In the past, the Amu Darya deposits (lacustrine facies) and sediments introduced by irrigation waters for the long-term history of agriculture played the main role in its formation [7]. Evidence of the latter in various parts of old riverbed of Daudan and, especially, in the areas close to settlements, are the remains of broken pottery from earthenware, found in agro-irrigation layers of soil.
Proceeding from above, it follows that the study of group and fractioncomposition of soil organic matter in connection with anthropogenic activity at different stages of formation of hydrological regime under different conditions is of great interest.
Analysis of group and fraction composition ofhu-mus was conducted according to the Tyurin'smethod in modification byVV. Ponomareva and T. A. Plot-nikova, and the qualitative composition of humus was classified according to "Methodical instructions ..." by M. M. Tashkusiev [6].
At the site under research, virgin gray-brown typical soils, freshly irrigated gray-brown, gray-brown-
meadow and meadow-marsh soils of the Tashsakin plateau with morphogenetic features characteristic for them are studied [5]. Old-irrigated meadow soils are studied in the alluvial-lacustrine facies of the Daudan riverbed.
Results and discussions. As is evident from the studies, in spite of the fact that in irrigated meadow gray-brown soils of the plateau and old-irrigated meadow soils of old riverbed of Daudan, due to intensive decomposition of organic matter characteristic of desert zone soils, the quantitative parameters of humus are insignificant — from 0.450 to 0.873%; various variants of the redistribution of carbon of organic acids are notedin its qualitative and fractional composition, due to the conditions of soil formation.
Analysis of the humus content in virgin gray-brown soil, taken as a reference, shows that the type of humus is a humate-fulvate one — Cha/C£a -0.59-0.87 in the upper humus-accumulative part of the profile (Table 1). In total, the hydrolysable substances account for 55.38-61.82% of the carbon amount in the fine-grained part of the profile.
In the fractional composition of humic acids, fraction II, which is related to calcium, is predominant: 7.44-19.31%. Fraction III, related to clay minerals and sesquioxides, is 4.06-8.05%. Fraction I of free humic acids is 1.54-2.20%, which indicates a weak degree of humus formation.
Against this background, it is obvious that humic acids are most strongly bound in the form of calcium humates and clay minerals, which is observed in the Malikchul soils [3].
Among the fulvic acids, fraction II, which is related to calcium -12.3-20.9%, prevails against the background of a low content of fraction III-2.78-5.18%.
I-a and I fractions occupy intermediate position, in sum making 13.5-17.21%, theyprevail over fraction II related to calcium. The predominance of fractions I-a and I in the horizon of clay formation of gray-brown soil is evidently due to the intensity of the flow of new formation of humic substances under severe hydrothermal conditions.
Table 1. - Fraction-group composition of humus in soils of the Tashsakin plateau and old riverbed of Daudan
Depth, Total Fraction of humic acids Fraction of Fulvic Acid C + h.a
car-bon,%
cm 1 2 3 Sum 1a 1 2 3 Sum Cf f.a Cf.a
Section - 1. Virgin gray-brown soil
0-1 0.1170 1.54 19.31 4.96 25.81 9.23 4.27 12.31 3.76 29.57 55.38 0.87
1-8 0.1261 2.30 1498 4.28 21.56 9.43 7.78 15.54 3.25 36.00 57.56 0.59
8-21 0.1330 1.73 7.44 4.06 13.23 8.95 6.99 21.43 5.18 42.55 55.78 0.31
21-41 0.0969 1.86 13.31 8.05 23.33 14.45 0.52 20.85 2.78 38.60 61.82 0.60
Section - 2. Freshly irrigatedgray-brown soil
0-26 0.3042 0.59 13.41 8.64 22.64 1.77 3.06 2.26 4.04 11.13 33.77 2.03
26-40 0.1922 0.62 14.788 4.32 19.72 4.47 2.87 8.53 6.03 21.90 41.62 0.90
40-70 0.0386 3.11 2.58 4.40 10.09 11.14 3.88 13.21 8.81 37.04 47.13 0.27
Section -12. Freshly irrigated gray-brown-meadow soil
0-22 0.2450 0.94 23.38 8.45 32.77 1.75 6.41 3.18 7.63 18.97 51.74 1.73
22-36 0.0933 1.93 32.26 15.97 50.26 9\8.04 10.18 15.54 5.36 39.12 89.38 1.28
36-60 0.0785 1.53 12.35 9.04 29.92 6.88 3.56 12.61 4.58 27.63 50.55 0.83
Section - 14. Freshly irrigated meadow-marsh soil
0-30 0.1117 2.59 23.9 16.02 42.51 7.69 3.41 11.72 11.72 34.54 77.05 1.23
30-40 0.0724 2.48 18.37 11.46 32.31 8.97 0.13 9.98 4.55 23.63 35.09 1.36
40-82 0.0607 2.96 13.51 11.36 27.83 3.46 7.08 7.41 5.60 23.55 51.38 1.18
Section - 16. Old-irrigated meadow soil of old riverbed of Daudan
0-30 0.4444 0.52 15.79 7.94 24.25 1.68 2.03 3.14 4.34 11.19 35.44 2.16
30-70 0.3106 0.58 21.28 6.31 28.17 2.76 0.81 3.21 4.18 10.96 39.13 2.57
70-85 0.2197 0.54 15.25 7.55 23.34 3.91 0.18 5.14 3.77 13.00 36.34 1.79
A different picture in the qualitative composition of humus is observed in freshly irrigated gray-brown meadow soil of the Tashsakin plateau. Against the background of a smaller number of hydrolysable substances — 33.77-47.13%, in the qualitative composition of humus, significant changes occurred in these soils as a result of irrigation. Humus of the arable horizon is represented by humate type — Cha/ Cfa — 2.03. Humus of the underlying "В1" horizon is of humate-fulvate type, and in the horizon "В2" it is of fulvate type.
Humic acids are mainly represented by calcium humates — 13.4-14.78% in the humus-accumulative part of the profile. Intermediate position among humic acids, as in virgin analogues, is occupied by
fraction III against the background of too low content of free humic acids in I fraction.
In the composition of fulvic acids, the same pattern is observed as in the case of a virgin analogue of gray-brown soil, that is, the fraction II related to calcium is prevalent. Intermediate position has the sum of I and I-a fractions-4.83-14.02% of the carbon amount. However, in fraction III, related to clay minerals and sesquioxides, there is some increase in its amount compared to virgin gray-brown soil, the content of which is 4.04-8.8% of the carbon amount. Apparently, irrigation, strengthening the soil-forming process, especially in the upper humus-accumulative part of the profile, led to a change in group composition of humus due to the formation
of humic substances firmly related to organomineral part of soil.
The transition of soils of the automorphic series to a semi-hydromorphic and hydromorphic ones, i.e. irrigated gray-brown soils to gray-brown meadow and marsh-meadow soils with a change in their mor-phogenetic properties, leads to a significant increase in the content of hydrolysable substances, especially due to humic acids (sections 12 and 14). The content of humic acids in the most biologically active part of the profile - in horizons "AJ and "B" is from 32.77% to 50.26% of the carbon amount. Among them, the largest portion is allocated, as in previous soils, to humates of calcium of fraction II and humic acids, tightly related to organomineral part of soil - fraction III. Among fulvic acids, which in the total amount to 18.97-39.12%, a large portion is allocated to fraction II. However, fraction III-7.63% prevails in the arable horizon of gray-brown-meadow soil (section 12), and fraction II - 15.31% (fulvic acids related to calcium) prevails in meadow-marsh soil (section 14).
So, the fixation of humic substances in freshly irrigated gray-brown soils of different water content regime occurs due to humates and fulvates of calcium - in the arable horizon, and in the lower horizons - due to free fulvic acids related to sesquioxides and aggressive fractionI-a. The latter finds its clear expression in meadow-marsh soil (section 14).
In old-irrigated meadow soils formed on alluvial-lacustrine deposits of Daudan, the humus formation is due to fractions II and III of humic acids. Free humic acids of fraction I are characterized by a low content - 0.54-0.58% of the carbon amount. Among fulvic acids, there is a tendency to reduce the amount of fraction II, and fraction III, related to clay minerals and sesquioxides, remains at the level of 3.77-4.34%, that is, the same as in virgin gray-
irrigated meadow-marsh soils, with the exception of their arable horizon.
In terms of the content of total amount of hydrolysable substances, the old-irrigated meadow soils-differ in smaller values - 35.44-39.13% than freshly irrigated gray-brown meadow and meadow-marsh soils. At such content, most of the hydrolysable substances are formed by a group of humic acids, which in total amount to 23.34-28.17%. An amount of fulvic acids in humus-accumulative layer representing the agro-irrigation horizon is 2 times less - 10.96-13.00% than humic acids. Therefore, the ratio C /C, is equal
' h.a f.a T-
to 2,16-2,37, that is, its magnitude is higher and the type of humus is represented as a humate one.Such a singularity of humus was noted in earlier studies by V. V. Valiev and S. Sidikov [1], in residual-marsh soils of the Amu Darya delta, periodically flooded for irrigated pastures. The fulvate-humate type of humus with a ratio of Cha/ f equal to 1.55was observed by N. R. Sharafutdinova [8], in irrigated meadow-alluvial soils of the lower part of the Amu Darya delta.
Conclusion
Thus, the above analysis of the composition of organic matter of soils in the Pitnyak oasis in connection with the statements inscientific literature suggests that intensive irrigation, which affected the hydrological regime of soils, led to significant changes in group and fraction composition ofhumus. The transition of fulvate humus to humate-fulvate one, and then to fulvate-humate one, along with an increase in the content of hydrolysable substances, is an evidence of an improvement in the quality of organic matter.
In old-irrigated meadow soils of alluvial-lacustrine facies, which differ in their relative cultivation, humic acids (among the hydrolysable substances) show a primary role in humus formation, creating the strongest bonds in the form of calcium humates and organomineral compounds.
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