A.N.Morozov

EXAMPLES OF USING WATER-SALT REGIME (WSR) MODELS

Forecasts of soil water-salt regime at irrigation.
Individual examples given below are the results of numerous forecasts with application of adapted to the natural conditions of the Central Asia region models of moisture-salt transfer in soils. Those are described on the pages of "Imitation models of soil water-salt regime", "Water-salt regime forecast methods", "Parameters adopted in the models to calculate a water-salt regime" sections.

A) Modeling of long-term irrigation with observance of agrotechnical requirements.
On figure1, as examples the results of forecasting cotton irrigation regime under the conditions of the Surkhandarya region are shown. In this it is shown how at irrigation required irrigation rates vary under the half-hydromorphic conditions over a number of years if in a root-inhabited layer moisture regime and salts concentration in a soil solution are formed, which is completely meet the requirements of agrotechnics.
At the beginning of the design period, when the initial salt reserves were little, water demand in order to keep assigned moisture and salts regime was somewhat lower than that was formed since forecast 3-5th years. If the original salt reserves were high, the need for irrigation water would be on the contrary higher than the steady-state one. While planning for outlook, obviously, one should accept a steady-state regime.

Figure 1. Results of a series of forecasting required irrigation rates to keep similar water-salt regimes in a soil root-inhabited layer for various initial soil salinity degrees (Surkhandarya region).

B) Modeling high-mineralized irrigation water influence on irrigation regime changes.
Basing on numerous series of forecasts for diverse soil-meliorative conditions, dependence of an irrigation rate for keeping set agrotechnical conditions on irrigation water mineralization is defined. In figure 2, as an example it is shown how total water consumption and water use vary depending on irrigation water mineralization (rates established in time, that is at continuous using irrigation water of set mineralization during years of time.

Figure 2. Dependence of an irrigation rate's component on irrigation water mineralization.

C) Possibilities for alternative annual use of water resources for irrigation.
Altering operation mode of the long-term regulation reservoirs cascade in the Syrdarya river basin and partially in the Amudarya river basin for the last decade, owing to their transition from irrigation of energetic schedule of discharges, causes tightness in conducting vegetation irrigation, especially in years of mean and low water level. Agricultural producers experience considerable lack of irrigation water in the driest and hottest months of vegetation ? June and July. How should one draw optimal schedule for crop irrigation so that to mitigate irrigation water deficit in these months, advisably without crop losses?
Experience of farmers in irrigation systems taking water from small rivers flood of which begins in early spring and runs out at the right beginning of summer, says about necessity of executing moisture-charging irrigation, and on lands subjected to salinity ? moisture charging preventive irrigation. When is it most efficient and economical to implement these arrangements in different climatic zones of the republic under the conditions of the altered (energetic) operation schedule of the reservoirs? What is the efficiency of these arrangements for soils different by hydromorphic natures? How to achieve the most efficient use of limited irrigation water resources?
Without touching on the issues of water saving with application of antifiltration measures in canals, reasonable techniques and technologies of irrigation execution, which are too important and independent measures, we will cite examples of possibilities for forming water-salt regime of soils by means available at farmers? disposal: irrigation terms and rates regulation.
We have carried out such a work for a most wide range of the natural conditions in Central Asia. It is known that soil moisture accessibility is conditioned by both its availability in a soil root-inhabited layer in a period necessary for plants and its quality, i.e. mineralization extent.
It turned out that it is possible to use quite effectively the existing in surplus autumn-winter-spring water resources under the conditions of automorphic, semi-automorphic, and hydromorphic soils, where groundwater mineralization effects in different ways on an irrigation regime.
In the article "On moisture-charging irrigation roles in increasing water supply to irrigated lands" you can get in more detail familiar with the results of these forecasts.

D) Forecasting irrigation water consumption under various conditions of territory draining.
Forecasting the dependence of an irrigation rate (namely, a rate without costs to losses on a field at conducting irrigation with imperfect irrigation technique) set in time subject to an assigned drainage degree (drainage intensity) is interesting. As the forecasts showed, an irrigation rate ensuring plants? agrotechnical demands greatly depends on drainage intensity, and it is the higher, the worse is the drainage degree. Figure 3 illustrates this for typical conditions of the Golodnaya Steppe under different groundwater tables.

Figure 3. Dependence of the irrigation rate that ensures alternative moisture regime on the drainage degree and location of the groundwater table.

The materials given demonstrate possibilities of modeling a soil water-salt regime in many diverse aspects. These forecasts may be usable at planning natural experiments. In fact, it is possible to consider in narrow terms and with little time expenditure all thinkable variants of an experiment and select just those for a field test, which can answer the assigned investigation tasks indirectly and in short times.

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