CC BY
16
Kholbaev Bakhrom Ernazarovich, Teacher of soil sciences, faculty of Natural Sciences Gulistan state university, Gulistan city, Syrdarya region, Uzbekistan,
E-mail: [email protected].
Prof. Namazov Khushvakt Karakhanovich Candidate of biological sciences, Tashkent State Agrarian University
E-mail: [email protected]
SOIL-AMELIORATIVE FEATURES OF THE DJIZAK STEPPE
Abstract: Based on field soil-ameliorative and laboratory-analytical studies, the main properties and ameliorative state of the soils of the foothill plain of the Golodnaya Steppe have been studied, within the territory of the Djizak steppe. The article gives data on the mechanical composition, chemical and agrochemical properties, the content of gypsum and C02 carbonates, generalized the salinity of soils, the patterns of their manifestation in different geomor-phologic regions of the steppe. The characteristic of the modern salt accumulation is given in connection with the development of irrigation of the territory, as well as the peculiarities of the manifestation of secondary salinization on irrigated lands.
Keywords: foothill plains, irrigation, mechanical composition, ground water, secondary salinizatoin, ameliorative state of soils, degradation, amelioration.
Introduction.
One of the large and promising areas of ameliorative constructions in Uzbekistan is the Djizak steppe, where of the total area of314.000 hectares of land and it is planned to use 219.000 hectares for irrigation, including 57.9 thousand hectares in the first place, the remaining area as unsecured in currently the water resources, belongs to the distant future. Being the southern extremity of the Golodnaya Steppe, it is a foothill plain with absolute elevations from 310 to 500 m and even more. In view of the absence of large water arteries, the need to supply irrigation water here by pumping and the availability of more convenient for irrigated farming in the Golodnaya steppe, the development of irrigated agriculture and irrigational land improvement in the Djizak steppe hampered the soil relief. Here, small-oasis irrigation was developed, based on the use of the constantly operating small mountain rivers Sangzar and Zaaminsuv. Now, when the soils of the flat areas of the Golodnaya Steppe are almost completely developed, the expansion of irrigated agriculture in this region is possible only at the expense of foothill plains. The current power supply capacity, as well as the accumulated experience of irrigation and ameliorative construction in the Golodnaya Steppe, made it possible to implement a waterfall into the Djizak steppe by pumping stations from the South Golodnostepsky Canal. In the successful solution of the tasks set by the Government of the Republic for the further development of agriculture and the implementation of the Food Program, development and introduction of a scientifically based farming system is of great importance. The vast territory of the Jizzakh steppe is characterized by a great variety of natural and economic conditions and resources for agriculture. Neverthe-
less, irrigation of new land is often associated with the solution of the problem of combating soil salinization. Until now, the researchers had the opinion that the foothill plains, due to significant slopes of their surface and natural drainage and dismemberment during irrigation, are guaranteed from secondary salinization. However, the experience of irrigation of individual massifs and foothill areas showed that this provision is erroneous [13; 1; 12], which results, in the main, from insufficient study of such territories. As V. V Yegorov notes [5; 6] the foothill plains have not been sufficiently studied for irrigation and melioration purposes, many important issues have not been solved yet, and therefore the ameliorative evaluation of them is complicated by very simplified, often with unjustified notions. The Jizzakh steppe is not an exception in this respect either. The first researchers of the Djizak steppe (Golodnaya Steppe) noted the presence of saline soils here in varying degrees [9; 20; 14; 15; 7; 8; 2; 3; 16; 17; 18]. However, the problems ofthe genesis of salinization, the role of lithologic-geomorphological, hydrogeological conditions and irrigation in the movement of salts and the formation of saline soils in the steppe, as well as the prevention of negative impacts on irrigation soils, on the soils of irrigation of the upper land of the Tajikistan part of the Golodnaya Steppe have not been adequately studied. In view of the lack of experience in the widespread development of the foothill plains, the issues of the sequence of land development and the expedient placement of agricultural crops were insufficiently justified. Therefore, only a careful study of lithologic-geomorphological, soil-climatic and hydro-geological conditions of the Djizak steppe, revealing the true amount and composition of water-soluble salts in soil of different genesis and lithological
composition of the aeration zone will allow us to discover the causes of salinity, establish the patterns of migration and accumulation of salts, in salinization under irrigation and scientifically justified to solve issues of land reclamation.
Objects and methods of the research
To solve a set of issues, we have conducted studies in the Djizak steppe for several years (1973-1977, 1993-1996). Investigations covered the least studied and poorly used in irrigated land the eastern part of the steppe, adjacent to the northern slopes of the Turkestan Range in the south, up to the Lomakin Plateau in the west and to the South Golodnosteppskiy Canal in the north, with a total area of about 90,000 hectares. Studies were carried out by laying soil sections located in linear alignments that crossed the territory from south to north. The stems of the soil sections were laid with the account of geomorpho-logical, hydrogeological and soil conditions. In total, four sections, each 20-22 km in length and consisting of 16-20 soil sections, are laid on the investigated territory. The first section of the soil sections covers the territory of the cones of the Lomakin plateau, the second one covers the Zaamin cone, the third one covers the right wing of the Zaamin cone of removal on the line of contact with the Khavast cone of removal. The fourth point characterizes the trail zone of the deluvial-proluvial plain of the Khavast group of rivulets. A total of 108 deep soil sections (in two stages) are laid on the territory, which reveal the entire aeration zone of soil soils (to groundwater) or to a continuous pebble horizon. Of all the soil sections without a pass through the genetic horizons, soil and ground samples and groundwa-ter samples were selected in case of their opening. In selected samples ofsoil in the analytical center was conducted, according to the generally accepted method of the Soyuz NIIHI (now UzPITl) [10; 11], and the methods described in the manual of E. V. Arinushkina [1], the study of their granulometric and salt composition, the content of humus and nutrients. In groundwater samples, the degree of their mineralization and the composition of the salts were determined. The research is based on comparative-geographic, comparative-geochemical and comparative-ameliorative methods for studying soils. The obtained results of field and laboratory studies of the soil of the territory using the materials of engineering-geological and hydro geological studies [21] made it possible to carry out a schematic soil-ameliorative zoning of the territory, which served as a basis
Table 1. - Hydrogeological
for predicting possible changes in the ameliorative state of soils during irrigation and differentiation of the recommended agro-ameliorative measures aimed at their optimization.
Results and discussions
Hydro-geological conditions of the Jizzakh steppe, as well as the entire arid zone many of the important production properties of soils, such as the degree and nature of salinity, humus content, field moisture capacity, water permeability, etc. These properties of the soil in turn determine the nature and extent of the required developmental and ameliorative measures (drainage, washing), as well as irrigation, irrigation and washing norms and irrigation regime. Proceeding from this, the most common basis for dividing the soils of the described territory was the nature of their moistening. On this basis, automor-phic, semi-hydromorphic and hydromorphic soils are distinguished here. Automorphic soils are developed in conditions of deep (5-10 m and more) occurrence of groundwater and their moisture is determined solely by atmospheric precipitation. Semihydromorphic soils are developed under conditions of weak ground moistening at a depth of groundwater within 3-5 m. Hydromorphic soils are developed in areas with close (1-2 m) groundwater. In connection with the dynamism of the hydrogeological conditions of the Jizzakh steppe, in the described soil belts, especially in the belt of light gray soils, transitional soils of meadow-grey brownish and grey brownish-meadow are observed. Intensive approximation of the level of mineralized groundwater (LMG) to the day surface and their consumption mainly for evaporation promoted the formation of meadow soils with varying degrees of salinity and negative elements of the alkali soil relief. In addition to hydromorphic alkali soil, residual alkali soils are also described in the area under consideration. These are soils in which the alkali soil process has stopped and salt accumulation is relict. The territory of distribution of these soils in the geological past experienced hydromorphic conditions, and then probably, due to tectonic processes, they dropped to a depth of 6-10 m. Thus, the classification ofsoil in the territory is presented as follows (Table 1). A great variety ofgeomorphologic-lithological, hydrogeological and soil-climatic conditions of the territory caused the variegation and complexity of the soil cover in terms of mechanical composition, agrochemical properties, salinity, gypsumation of alkalinity and others. conditions of soil formation
Soil Hydrogeological conditions of soil formation
Depth of ground water, m. Effect of soil moistening on soil formation
1 2 3
I. Automorphic soils:
1. Typical gray-brownish soil > 10 No influence
2. Light gray-brownish soil s 5-10 h>10 No influence or very weak
1 2 3
II. Semihydromorphic soils:
1. Meadow-gray brownish soil 3-5 Weak
2. Gray brownish-meadow soils 2-3 Moderate
III. Hydromorphic soil:
1. Meadow 1-2 Intensive
2. Alkali 1-2 Intensive
The mechanical composition of meadow-gray brownish soils is heterogeneous and differs in each geomorphological region in its own and features. Loess type sediments characterized by uniformity and predominance of dust particles in the mechanical composition are characterized by the Zaa-min cone of removal and the Lomakin plateau. The content of fractions of coarse dust (0.05-0.01 mm) is from 26-33% to 56-58% with a very low amount of sand fractions. The silt content (<0.001 mm) varies within a wide range from 9-10% to 18-19% (Table 2). Gray brownish-meadow soils formed on deluvial-proluvial layered sediments of very variegated
texture. Heavy loams (section 7) alternate with medium and light loams, and in other cases sandy loamy soils in the upper horizons, to the bottom, will be replaced with heavy loams (section 24), the content of the silty fraction of gray brownish-meadow soils varies widely from 0.6-0.9% to 11-13%. Meadow soils are formed on deluvial-proluvial deposits of very variegated texture. Medium loam alternates with light, heavy, sometimes clay and sands (Table 2, sections 24, 2, 3, 22). The mechanical composition of soils is in most cases represented by medium and light loams. Heavily loamy and sandy loam varieties are very rare.
Table 2.- Mechanical composition of soils
No. Fraction content in% on absolutely dry soil, fraction size in mm
Sec- Depth, cm Sand Dust Silt Physical clay
tion > 0.25 0.25-0.1 0.1-0.05 0.05-0.01 0.01-0.005 0.005-0.001 < 0.001 < 0.01
1 2 3 4 5 6 7 8 9 10
Meadow-gray brownish
0-30 1.0 1.1 13.5 50.2 10.5 13.2 10.5 34.2
30-50 0.6 0.8 9.3 58.3 8.1 12.3 10.6 31.0
17 50-85 0.5 0.8 11.7 56.6 8.4 11.1 11.5 31.0
85-125 0.9 2.2 25.5 42.5 8.7 9.8 10.4 28.9
125-170 1.5 1.4 16.4 56.0 6.0 9.7 9.0 24.7
170-200 0.6 0.6 6.5 56.3 11.2 12.3 12.6 36.0
0-30 1.4 0.6 13.0 20.3 17.3 8.7 9.0 35.0
30-50 2.0 0.6 21.8 26.7 17.8 18.5 13.2 49.5
32 50-95 1.9 0.2 19.1 26.3 19.1 13.6 19.8 52.5
95-130 3.8 0.7 38.7 33.2 4.4 12.5 12.7 29.6
130-165 1.2 0.4 23.3 31.5 4.3 25.4 13.9 43.6
165-200 0.7 0.8 17.4 33.0 8.6 25.4 19.8 53.8
Gray brownish-meadow
0-35 0.7 3.1 6.1 39.7 17.7 28.8 3.9 50.4
35-73 7.6 4.5 6.0 33.5 18.7 29.3 0.6 48.6
7 73-105 11.9 9.3 10.2 47.3 12.3 0.7 8.3 21.3
105-150 0.9 16.0 24.5 29.3 9.2 9.5 11.6 30.3
150-200 0.2 11.3 16.1 32.2 6.9 8.8 4.7 20.4
0-26 3.7 0.7 42.7 36.6 3.9 8.7 3.1 14.7
26-60 5.3 2.2 38.5 37.2 3.9 5.0 7.9 16.8
28 60-96 12.8 1.6 26.3 34.9 13.8 9.7 0.9 24.4
96-130 7.0 2.2 36.4 18.2 9.3 13.6 13.3 36.2
130-165 5.1 0.5 27.3 15.7 11.7 28.6 11.6 51.9
165-200 4.8 0.8 21.5 27.4 14.8 22.6 8.1 45.5
1 2 3 4 5 6 7 8 9 10
Meadow
24 0-30 9.8 5.9 22.1 27.8 7.0 19.1 8.3 34.4
30-48 14.3 4.7 18.4 24.2 9.2 16.0 13.2 38.4
48-103 13.4 6.4 22.1 34.7 6.1 7.8 9.5 23.4
103-145 7.8 0.1 22.4 35.0 9.0 15.4 10.3 34.7
145-175 15.5 1.9 9.1 17.6 23.8 20.0 12.1 55.9
175-200 9.6 1.5 37.8 36.4 10.8 5.6 7.3 23.7
2 0-25 0.7 0.9 21.8 45.0 8.1 19.5 3.5 31.1
25-45 2.6 2.7 19.9 47.3 6.5 11.5 7.7 25.7
45-76 10.5 4.0 18.1 31.5 12.2 13.8 8.1 34.1
76-115 10.8 3.5 13.9 36.0 9.9 11.2 15.7 36.8
115-152 15.7 4.4 16.8 34.9 5.1 10.8 10.5 26.4
152-176 12.1 2.3 16.7 42.3 5.6 7.8 13.2 26.6
176-200 14.6 2.9 14.3 27.4 7.1 16.2 15.7 39.0
Meadow-alkali
3 0-27 7.3 6.8 9.5 33.3 13.5 26.8 2.8 43.1
27-50 7.1 6.6 14.7 32.2 16.7 21.9 0.8 39.4
50-90 11.9 3.6 11.1 25.5 27.6 20.0 0.4 47.9
90-120 6.1 1.6 9.3 19.5 37.1 25.4 1.0 63.5
120-170 0.04 0.2 3.0 30.2 29.7 26.7 10.1 66.5
170-210 0.07 0.1 2.0 34.6 24.4 28.2 10.8 63.4
22 0-28 4.0 4.8 15.4 33.2 10.5 10.3 21.8 42.6
28-50 7.8 4.1 22.4 31.0 9.0 15.4 10.3 34.7
50-80 3.6 0.4 34.6 36.2 9.2 12.7 3.3 25.2
80-118 3.5 0.3 46.1 27.1 6.1 11.5 5.4 23.0
118-160 4.0 0.6 44.4 34.0 6.1 6.0 4.9 17.0
160-200 8.2 0.6 49.8 27.0 3.8 8.2 2.4 14.4
The predominant fraction of the described hydromorphic meadow soils, as in gray-brownish soils, is large dust (0.050.01 mm), the number ofwhich reaches 50%. The silt content in individual horizons reaches 21% (Table 2, Section 22).
The described soils in terms of the upper 30 cm thickness are mainly represented by medium and light loams, less often heavy loams underlain by layered sediments (Table 2). Alternation of these layers can be clearly traced along the entire 3-5 m thick soil, consisting of light, medium and heavy loam, sandy loam, sand and clay in places. In all studied soils, a rather high
content and uniform distribution of coarse-grained (0.05-0.01 mm) fractions with their variation in a five-meter thickness of soil from 30-33 to 60%. Even in lighter sandy soils of soil soils, a high content of coarse-grained particles is observed. A. N. Ro-zanov [19], who studied the features and origin of the parent rocks of this part of the Golodnaya Steppe, also noted that the fraction of large dust contained in an amount of40-80% is the main component of all layers, regardless of their membership in sandy loam or loam. The second place belongs to the fraction of fine dust and the third-clay fraction.
Table 3.- Chemical and agrochemical properties of soil
No. section Depth, cm Hu-mus% C: N Gross,% Mobile, mg/kg C02 Carbon- ate,% CaSO^ •2H2O (Gypsum) pH aqueous
N P K PA K20
1 2 3 4 5 6 7 8 9 10 11 12
Meadow-gray brownish
17 0-30 0.721 4.4 0.095 0.124 0.844 14.0 120 5.80 14.40 7.36
30-50 0.583 5.3 0.064 0.138 0.769 26.0 200 6.40 16.03 7.42
32 0-30 0.996 6.0 0.096 0.132 1.575 5.4 302 4.10 3.33 7.54
30-50 0.615 4.9 0.073 0.092 1.251 4.9 320 4.15 2.08 7.51
1 2 3 4 5 6 7 8 9 10 11 12
Gray brownish-meadow
7 0-35 1.346 5.8 0.135 0.170 0.967 17.0 180 5.58 12.61 7.76
35-73 0.887 4.8 0.107 0.120 1.306 14.0 190 5.70 13.70 7.86
28 0-26 0.898 5.4 0.096 0.220 0.583 16.0 238 5.75 18.55 7.68
26-60 0.545 4.2 0.075 0.096 0.608 6.0 130 5.37 18.91 7.34
Meadow
24 0-30 1.441 5.7 0.218 0.189 0.601 7.0 325 5.03 3.94 7.82
30-48 1.197 5.0 0.138 0.200 0.892 4.0 325 4.93 4.37 7.36
2 0-25 0.982 5.9 0.097 0.189 1.575 5.8 484 4.99 14.53 7.52
25-45 0.875 5.6 0.090 0.148 1.483 5.3 424 5.98 15.37 7.21
Meadow-alkali
3 0-27 1.380 6.4 0.125 0.106 2.988 4.1 328 5.44 3.85 7.48
27-50 1.191 4.5 0.153 0.112 3.740 5.1 440 5.18 14.99 7.63
22 0-28 0.095 6.6 0.086 0.112 0.680 6.0 220 5.35 5.06 7.74
28-50 0.879 4.9 0.104 0.106 0.563 4.0 180 5.00 5.56 7.82
In relation to humus content, the soils under consideration are of great variety. Depending mainly on the salinity of the mechanical composition, the humus content in the upper arable and sub-plow layers is from 0.545-0.583 to 1.3801.441%. The amount of humus below the arable horizon, with a rare exception, as a rule, decreases. In accordance with the degree of humus content, the content in nitrogen soils also changes (Table 3).
Conclusion
1. The complex geomorphic structure of the investigated area also determined no less complicated hydro geological processes, that the ground waters formed, as well as a large number of surface irrigation waters, do not have or have a very weak outflow and are mainly used for evaporation and transpiration, and this leads to intensive salt accumulation on a large part of the area and consequently to the general unfavorable ameliorative state of irrigated soils.
2. The intensive irrigation that began in the last 35-40 years radically changed the hydro geological conditions of the area and as a result of the loss of a large quantity of irrigation water from the canals and from the irrigated fields, a sharp rise in the groundwater level occurred. The high waterfall for irrigation accelerated the transformation of automorphic soils into semi-hydromorphic and hydromorphic and soil cover of the territory at present is represented mainly by meadow-gray brownish, gray brownish-meadow, meadow soils and alkali, differing in mechanical composition, the nature of the underlying rocks, salinity, depth of occurrence and mineralization of groundwater eats natural and artificial drainage, agrochemical properties, which indicates the unevenness of the ameliorative state of soils.
3. Depending on the conditions of relief, lithologic-geomorphological and hydro-geological conditions and the nature of soil-forming stocks, semihydromorphic (meadow-gray-brownish) and hydromorphic (gray brownish-meadow and meadow) soils with different salinity degree were distinguished in the soil cover with a predominance of medium, strong and very strong salinity.
4. A great variety of natural and irrigation-farming conditions of the area where secondary salinization is increasing is now defining a great variety in its manifestation, both the qualitative and quantitative composition of the salt accumulations, and the intensity and general direction of the salinization process. On the whole, the variegation of salinity is observed along the profile of soil and space, showing the alternation of slightly saline and medium saline soils with strong, very strong salinity, places and alkalis. Among the described soils, it is now possible to single out all possible variants both in terms of the degree and type of salinity, and the position of the salt horizon.
5. The amount of humus in the profile of the described soils does not exceed 1.380-1.441%, they are very low and low-provided in the content of mobile phosphorus, and the exchange of potassium is mainly medium and high-yielding. The carbonate profile forms two maxima - from the surface and in the transitional carbonate-illuvial horizon, where the carbonate content in CO2 reaches 5-6%. Gypsum in the lower and upper parts of the profile is manifested in various amounts. The reaction of the soil solution is slightly alkaline -pH = 7.3-7.8.
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