Morozov A.N.

 

CROP IRRIGATION REGIMES

Preliminaries
Here, we are going to touch closely on two questions, which so far are not considered when rationing water consumption and developing crop irrigation regimes:
- taking into account moisture-salt transferring in soils;
- taking into account features and consequences of application one or another irrigation technique.
We think until these problems are not considered somehow when making designs, schemes, feasibility studies, it is incorrect to talk about ways of solution of the Aral region problem, at least for Uzbekistan, Kazakhstan and Turkmenistan. So, let us consider:

1. Role of taking into consideration moisture-salt transferring in soils when designing crop irrigation regimes and making interpretation of field tests' results.
Taking for a basis of argumentation fundamental laws, determined by great M.V.Lomonosov as early as in the beginning of XVIII century, we will try to examine salt balance in soil if there is no salt withdrawal through drainage or to sub-horizons under following typical ideal conditions reflected in table 1.

Table 1

Indices	Units	Values
Deficiency of air moisture for a period of IV-IX months	m3/ha	10000
Evaporation-transpiration (cotton in the zone C-1-A)	m3/ha	6500
Including at the expense of irrigation water	m3/ha	4500
Mineralization of irrigation water	g/l	1,0
Salt arrival along with irrigation water for vegetation	t/ha	4,5

This (the last item of the table) amounts to approximately 0.3 % a year of soil meter layer's mass, out them around 1/3 part, or totally 0.1 % a year are toxic salts. That is, it is obvious, without salt withdrawal out of soil's root-inhabited layer it is impossible keeping long irrigated agriculture, since for several years the soil will become alkaline soil just because of salt arrival along with the irrigation water.
Passing "boring" story about how scientists came to the idea of leaching irrigation regime, we'll attempt to illustrate a concrete forecast (applying moisture-salt transferring models available) on how the requirement for irrigation water will change if to set the following terms and limits, shown in the table 2, and what formed regimes will be for many years.

Table 2
Terms and limits while modeling

Fig. 1.

Let us try to comment the figure:

a) Irrigation regime changes with time, approaching asymptotically to the steady one (characteristic of given terms).
b) Change of irrigation regime takes place as soil water-salt regime (SWSR) forms under given natural and technical conditions (in this example - towards increase of water use to keep stable SWSR; but, if to begin an experiment when the soil is too salted, the process will go to inverse direction, but, anyway, it will come to the steady regime).
Of course, these are forecasts on imitation models and no more, but, if anybody knows of conducting such experiments in field conditions, we could discuss their results. Our data can be considered as means of experiment planning.
c) If a test on determination of plant's requirement for water to be began on lands desalinized not enough, and conduct it for not longer than three years (common duration of tests, most likely, connected with the term of the executors' post-graduate course), so, obviously lowered values (compared to those, which will be required for further) of irrigation rates will be received. And if, herewith, to make an allowance for that generally post-graduate students leave for the field only during vegetation period, and by no way they can account when and how much water was be delivered in non-vegetation period, it becomes obvious why test data on relationship between crop capacity and water spending, collected by us from almost 300 publication works, are so ambiguous, that the dots on the relationship's schedule look like a "cloud".

Fig.2 Dependency of relative cotton crop (C/Cmax.exp.) to relative irrigation rate (M/D) according to test stations' data of former the Union's Research Institute of Cotton, Kara-Kalpak institute of agriculture and Tashkent Agricultural Institute.

And, when graphing it relative values of the crop (Crel = C/Cmax) and relative water expenses (M/D = Mac. /D) were used.
Here: moisture deficit (D = E0 - P) during a vegetation period in the year of conducting the experiment;
E0 -evaporability from water surface;
P - precipitation.
The indices marked by mean:
- rel. - relative value;
- ac. - actual value in the experience's variant;
- max. - maximum value in experience.

For the analysis only such experiences were selected, in which all other conditions became unchangeable, i.e. on an unchangeable "background" of fertilizers, agrotechnics, growth and etc., while the water factor only changes.
Depending on irrigation water mineralization, this process' dynamics can greatly change. But, if to compare steady irrigation rates, required maintaining adequate conditions for plant growing under various irrigation water mineralization (regardless of coming steady regime time), so, it is obvious, as irrigation water mineralization increases, under other equal conditions, requirement for irrigation water will grow.

When at the middle and down stream of the Amudarya and Syrdarya rivers mineralization reaches 1,5 g/l (that is 4-5 times higher than the fixed one on rivers' runout from mountains), it is time to take into account of this factor.

2. Influence nature of various kinds of losses upon soil water-salt regime and upon hydro-reclamation systems' infrastructure.
Irrigation water use efficiency in an arid zone, where more than 50 % of lands are subjected to salinization, is influenced too much by irrigation timeliness, even water distribution over the field area, as well as by way of its delivery. Nature of this phenomenon is discussed in the "Irrigation technique is a key to reclamation of salted lands" section, prepared by the site's author. Besides, this problem is discussed in detail from point of view of irrigation water use efficiency and concrete technological water spare size on the page prepared by a Doctor of Technical Science, Vitaliy Konstantinovich Sevryughin, in the "Irrigation technique and technology. New ideas and constructive decision" section, prepared by the site's author. It is in the second part related to forced extra draining capacities. As regards to influences of that inefficient expenses to reclamation state of irrigated lands, they are obvious enough and described in the literature. But, nevertheless, we shall dwell briefly on nature of that effect.
Regional and local groundwater pressures generally complement one another, and their nature on irrigated lands is ridden by inflow availability from outside, losses from the canals to filtration, laid on the commanding marks, as well as concentrated losses to deep filtration (Kostyakov A.N., Fjodorov B.V., Mikhelson B.N., Averyanov S.F. and others). This natural or arisen due to irrational system's construction pressure prevents seriously to forming normal water-salt regime.
In the "Influence of irrigation technique on reclamation state of lands" section an aspect related to inefficient water expenses during various irrigation methods on a field is considered.
After discussing preliminary observations we will proceed to searching water consumption normalizing ways and calculations of crop irrigation regimes, applying "instruments" available - the facts, imitation models of moisture-salt transferring, technical characteristics of various irrigation methods, and good sense as well.
In future, if this will interest anyone, we intend adding pages as follows:
- "The problem's background",
- "Adjusted standards",
- "Strategies being proposed",
- "New standards".

How to get in touch with us?

Return to the main pag