A.N.Morozov

SOIL-MELIORATIVE ZONING OF AN AREA

The soil-meliorative zoning system in the way as it stated below was born in the Soil-Meliorative Investigations Department of the former "Sredazgiprovodkhlopok" (Central Asian State Design Institute of Water and Cotton) under the direction of Vladimir Rikhardovich Shredder in 1965-1970 years. That shaped thus due to the production need. That was a period of mass development of virgin lands for irritation. One had exactly and competently to distinguish soils by their properties for designing proper reclamation measures. As far as competently and bona fide those designs were carried out is a question of another issue.
One should note that neither reclamation of new lands nor meliorative state monitoring of old-irrigated lands, whatever way made, cannot be realized correctly without basing on soil-meliorative zoning, which takes into consideration (synthesizes) basic climatic, geomorphologic, hydrogeologic, lithologic, hydrochemical, and soil-meliorative characteristics of a territory. All investigations conducted without taking into consideration soil-meliorative zoning can be likened to an attempt of creating a thermonuclear bomb by physicists who have secondary school level education. Soil-meliorative zoning is a system that allows finding out in what specifically diverse soil in one region differ one from another and in what similar soils in different regions are alike.
At soil-meliorative zoning, as stated above, the following soil constituent factors are taken into account, which determine conditions for irrigation and reclamation:
* climate;
* hydrogeological conditions;
* meliorative-farming conditions;
* lithologic-geomorphologic structure.
Differences of climatic conditions depend on latitudinal location and vertical zoning. For practical purpose of water consumption rating, the Central Asia territory divides into three zones: North (N), Central (C), and South (S), each of those subdivided into north (I) and south (II) parts. Distinguishing soil-climatic zones and belts is based on quantitative indices of precipitation amount, temperature mode, and air humidity.
In each climatic zone, belt-altitude zones are distinguished by vertical zoning. Their description is given Table 1, where, also, quantitative characteristics are cited in the form of natural moisture factors (Mf) that is the generalizing index of local thermal and water resources and are found via the formulae:

Mf = (�� + Ws)/��

here, PO - average many-year total of precipitation for a year's period with air temperature higher than + 5 Co, mm;
Ws - moisture reserve in a soil layer of 1 m at the begging of the designed period, mm;
Eo - evaporability during the designed period, mm.
Vertical zoning belts are distinguished by moistening conditions in a winter-spring period. Precipittion quantity from B belt to G belt increases and the natural moistening period become longer. A summer period and first autumn months are equally dry and a littlie differ by the temperature mode.

Table 1. Zoning of Uzbekistan territory by the moistening factor

Meliorative estimate of hydrogeological conditions is based on hydrogeological and soil-meliorative zoning, as a criterion for which is groundwater balance (present or designed) that is determined by the conditions of their feed and discharge (flow-out, transpiration, and evaporation). With an allowance for these indices, the following hydrogeological-meliorative regions are distinguished:
* a - secured outflow and transit of groundwater at deep location, not influencing on soil constituent;
* a1 - secured local groundwater outflow due to relief ruggedness;
* b - intensive external inflow, backwater, and pinching-out of groundwater with steady close location;
* c - difficult inflow and outflow of groundwater with unsteady location depth and regime not depending on local conditions.
In the regions "a" and "a1", soil-meliooprative situation is determined by relief conditions and lithologic composition of soil constituent strata. Their distinguishing is important only from the genetic standpoint, but it in no way has an effect on water losses to evaporation and transpiration.
In the regions "b" and "c", main differences are conditioned by water-cycle type (amount and activity of inflow and outflow) of groundwater and hydrochemical zoning related to that. Territories are differentiated subject to groundwater location and mineralization. Areas with flesh groundwater are marked with indices "b" and "c"; with mineralized groundwater (more than 5 g/l) with "b1" and "c1" in accordance with belonging to one or another hydrogeological-meliorative region.
The most steady in the complex of factors determining capacitive characteristics of soil moisture in relation to water and soil moisture's dynamic characteristics are properties of a soil constituent stratum correlated to considerable extent with its granulometric structure:
* aeration degree;
* water permeability;
* specific water retention;
* capillary properties;
* thermal mode; and others.
Sand and loamy sand soils have favorable air and thermal mode, are water permeable, but have low moisture capacity. Loamy soils have high moisture capacity and poor water permeability, bad water yield, high swelling, and adverse thermal features.
Loamy soils, being in middle, are the best by the properties and composition. They have favorable air and thermal modes, good water permeability, high moisture capacity, and mobility of soil moisture.
Differentiation of the irrigation regimes five principal groups of soil constituent strata are marked out, which noticeably differ by indices of water-physical properties:
* 1 - sand;
* 1a - low-thick, highly stony;
* 2 - loamy sand;
* 3 - light and medium-loamy;
* 4 - medium-loamy (dense) and heavy loamy;
* 5 - loamy.
Averaged values of soils? water-physical property indices characterizing the marked groups are presented in Tables 2 and 3.

Table 2. Water-physical characteristics of main types of ground

Table 3. Averaged characteristics of soil constituent strata of various granulometric structure soil constituent stratum

Soils of heterogeneous lithologic structure by moisture capacity and conditions of soil moisture expenditure are equated to the mentioned main groups in the following way:
* to the 1st group belong low-thick (0.2-0.5 m) loamy ones on sand-pebble deposits and on gypsums, and, besides, to the 1a group belong very low-thick, highly stony ones;
* to the 2nd - medium thick (0.5-1.0 m) loamy on sand-pebble deposits and on gypsums;
* to the 3rd - loamy, becoming lighter downward;
* to the 4th - loamy, becoming heavy downward;
* to the 5th - highly stratified with availability of loam.

Table 4. Hydro-module zoning by "Sredazgiprovodkhlopok" (V.R.Shredder, 1970)

Transition from the above-presented scale adopted by "Sredazgiprovodkhlopok" in 1970 to a "corrected" scale (used now for the purpose of most adequate reflection of natural conditions met when drawing maps of hydro-module zoning) is shown in Table 5.

Table 5. The "corrected" scale adopted at soil-meliorative zoning and its conformity with the V.R.Shredder's scale.

In this form, soil-meliorative zoning faces today many problems, which are to be solved by the next generation of scientists. This is, first of all, attaching the quantitative indices to many qualitative ones stated above. Who is familiar with the works by V.R.Shredder will note that we tried in tables 2 and 3 to add such indices related to soil physics, but, there is plenty of works to be done. There are a number of unknown indices, for instance, we can indicate the followings:
- degree of drainage (provision by natural or artificial drainage);
- dependence of soil leaching ability on its granulopmetric composition and state of the soil horizon.
- Influence of soils? pore space structure on regularities of absorbency and capillary rise; and so forth.

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