Morozov A.N.

PARAMETERS ADOPTED IN THE MODELS TO CALCULATE A WATER-SALT REGIME (WSR)
To forecast soil state upholding the restrictions dictated by the agrotechnics of cropping one or another agricultural plants, input information?s parameters, moisture-salt transfer models? parameters, and irrigation regime control models? parameters have to be replaced.
The accessory programs available allow creating an input file in a conversational mode using averaged parameters for the accepted soil-meliorative zoning that, after goal-oriented correcting, can be used in forecasting.
Input information parameters composed of:
- soil-meliorative and climatic indices of the object, which are relatively steady in time and assumed permanent for a forecast period;
- soils? initial state indices being transformed during forecasting;
- technical specification of a hydromeliorative system (actual or design);
- crop requirements to the conditions of vegetation, providing gaining the target crop capacity.
System state forecasting models must be provided with parameters, which enable sufficiently correct imitating the natural processes. In the moisture transfer model, among such parameters are:
- filtration factor and constants which determine the dependence of hydraulic conductivity on moisture;
- parameters characterizing soil capacitive properties and moisture potential in the soil;
- constants determining intensity of evaporation and transpiration by plants depending on soil moisture.
In the salt transfer model, the parameters determining the salts hydrodynamic diffusion factor should be defined:
- salts molecular diffusion factor;
- salts dispersion factor.
For the model of soil state control and irrigation regime control, the followings must be defined:
- root-inhabited layer depth in diverse plants growth phases and permissible values of the soil moisture?s total potential in these phases;
- starting and ending terms of an irrigation period;
- crop reduction factors at stress situations.
In character, the parameters mentioned above in the given list can be conditionally divided into three groups:
- sufficiently universal ones, not requiring for additional study;
- regional ones, typical of the investigated region;
- relevant to any case being considered, which is particularly specified every time.
Dwell on consideration of parameters necessary for the model to function. The input information will be elucidated in more details in the end of the section. A very important parameter in the moisture transfer model is the soil hydraulic conductivity factor, poorly studied for the region soils. Dependence of the factor on moisture, generalized according to the data of several authors (I.R.Pilip, 1975; R.Z.Kurze, Don Kirkham, 1962; V.N.Chubarov, 1972; U.J.Staple, 1972; I.S.Pashkovskiy, 1973; A.N.Morozov and others, 1975), turned out to be possible to accept for the model by the formulae of S.F.Averyanov (1978). According to his dependence, K(q) is determined by a filtration factor (Kf), porosity (m), wilting moisture (PWM), and the exponent n = 3.56. We selected the exponent within the range of 2-7 so that to provide the best approximation of experimental data reasoning from the properties of the soil-constituent stratum.
Values of porosity and moisture degree of moisture movement cessation in the liquid form have been accepted based on summarizing results of a number of works and study of soil?s water properties; values of the exponent n, as said above, were selected depending on conformity of the forecasted soil moisture regime with one observed under the natural conditions, and correspondence of the designed curves �(q) and �F(q) to the experimental ones.
As design indices of the filtration factor (Kf), it were used the averaged values suggested in the works by B.Y.Neyman (1974) for grounds of various granulometric composition of objects for irrigation in the Karshi and Golodnaya Steppes and other regions of Uzbekistan.
Dependence of the soil capillary-sorption potential on moisture has been accepted basing on summarizing a number of works by A.N.Morozov (1973), V.F.Safonov, A.N.Morozov (1975), A.N.Morozov, and others (1975). This dependence was defined (on the dehydration branch0 through the membrane press method in the range of pressure of 0 to 0.7 atm; within the range of 0.7 to 16 atm ? by the hygroscopic method (�.�.Globus, 1969); and higher ? it was determined by a calculation way (B.N.Michurin, 1975).
Accessibility of the soil moisture was estimated, as indicated above, according to its total potential. The osmotic component was computed via the dependence:

Pc(z) = P(z) + 0.36 * C(z)

here, P(Z) ? capillary-sorption potential in the soil moisture;
C(Z) ? soil solution mineralization.

Critical values of the total soil moisture potential (for determination of irrigation terms in the model of soil root-inhabited layer state control and irrigation regime control) are found through calculations based on the experimental data of S.N.Rijov, N.I.Zimina (1971), S.N.Rijov (1971). Via the curves of pF = f(q) determined by us, the values of the capillary-sorption potential in the soil moisture (not studied in the experiments) are detected and added to the factual values of the osmotic potential (pressure) ones got in these experiments, measured under the least moisture degree and corrected to the pre-irrigation moisture equal to 0,7HB.
As the calculations? results testify, the value of the soil moisture critical potential is determined for cotton in the range of 4-6 atm and does not practically depend on salts composition and a background of fertilizers. At low availability of nutrients, surplus concentration of soil solutions even leads to some comparative crop capacity rise.
A variation graph of soil layer depth for different crop growth stages is determined through in proper literature data. The following parameters (k) of dependence for calculation of the total evaporation were accepted:
- moisture of actual evaporation cessation (EM), close to the moisture of irreversible plants wilting pF = 3.7 or � ~ 5 tm.;
least moisture degree (HB) was defined at that as moisture at pF = 2.5, or � = 0.2 tm.(R.Slaycher,1970);
- factor b(t) reflecting total evaporation?s peculiarities of various crops; it is accepted taking into consideration of the work by D.F.Solodennikov (1981). In table 1, values of this factor are given for cotton;
- evaporability value of the water syrface (Ec) was computed by the known formulae of N.N.Ivanov (1954) with modification by L.A.Molchnanov (1955):

here, t - average monthly air temperature (C);
a - average monthly relative air humidity (%).

Table 1. Values of factor b(t), accepted for calculation of total evaporation.

To determine plants transpiration, the value of physical evaporation?s part out of the total one (a(t)) was accepted for cotton taking into account data of several authors (S.N.Rijov,1948; A.R.Konstantinov,1963).
In the salt transfer model, the factor of hydrodynamic dispersion (D) is applied. Under real conditions, salts migration happens at relatively great dispersion component (D*v) of the convective diffusion factor compared to the molecular diffusion factor (Do):
Do < = D*v; D ~ D*v
At that, parameter D reflects the internal structure of a filtering medium (F.M.Bochever, �.�.�radovskaya, 1974; N.N.Verighin and others, 1979):

D = b`*s
here, s - average typical size of the medium?s particles;
b` - non-dimensional parameter characterizing heterogeneity of porous medium.

Variation of parameter D weakly effects on a soil concentration (D.F.Shulghin, 1971; N.N.Verighin and others, 1979) and, at unconformity of a real process to the mathematical scheme, needs to be changed within very great ranges. That is why, every time when D is in the role of the only, universal parameter, it becomes over-estimated (according to some data, the one comes to tens or even hundreds of m2/day), which completely distort its original sense, laid in the convective diffusion equations. Therefore, there is a suggestion on D parameter estimation by the data of grounds? granulometric composition (V.A.Baron, Y.G.Planin,1974; N.P.Kuranov,1980). In these works shown that the heavier is a soil granulometric composition, the more is D, i.e. the hydrodispersion parameter D is proportionate to physical loam concentration in the soil. In table 2, D parameter?s values are represented advised by N.P.Kuranov (1980) for soils of steppe sort and accepted by us for calculation of the averaged value. Such an assumption can be considered justified for freely soluble salts and soils with low exchange capacity, which are actually all the soils in the Central Asia region.

Table 2
Values of D parameter suggested by N.P.Kuranov

The value of salts molecular diffusion factor, which relatively faintly influence on their dynamics, is assumed as average of various salts.
For use in the moisture transfer model, the linear flow dependence on a head is accepted, since it is the simplest, and is sufficiently often applied in like forecasts (A.I.Golovanov, 1979).

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