Morozov A.N.

Lecture 6. Total seasonal water requirement of plants and specifics of development of their different phases.

I am quite agreeable with advice of I.I. Pavlov: "raise hat in front of Mr.Fact". But not far from that would be an advice - put on hat and think twice on real value of the fact.

I.V. DAVIDOWSKIY

 

Possibly nobody will be against the fact that required amount of irrigation directly depend on climate conditions…
Let us start one after another, and begin from the question - how much water should be delivered to a field and the delivery schedule to get implied yield. First of all, let us have a look at Picture 2.1 where monthly average climatic characteristics of desert zone of Uzbekistan present there. You can find the characteristics for your own place in agro-climatic reference books at any time, and potential evaporation from water surface can be calculated by using simple formula if you can not find it in the same reference book).

Picture 2.1. Climatic characteristics and water balance deficit.
t - air temperature, Centigrade degrees;
Ю - relative air humidity in %;
нЯ; - atmospheric precipitations, mm.
еН- potential evaporation from water surface, Åî = 0,00144 * (25 - t)2 * (100 - a) ;
еН = 0,00144 * (25 - t)2 * (100 - a) ; - water balance deficit (colored with yellow for vegetation period).

Monthly average air temperatures development, amount of precipitation, relative air humidity, calculated evaporative rates and humidity deficits were shown on the picture. Area of the figure colored with yellow - is deficits of vegetation period (IV…IX months in this case). But each plant has its own date of seeding, vegetation period, and that is why water requirements for irrigations will depend on these amounts and stipulate its own irrigation period. I.e., short season varieties may require significantly less water to complete its seasonable cycle than long season crops, but it relates mainly not to perennial trees and bushes which require water during all vegetation period.

Though water deficit - is not requirement itself yet, but anyway, calculated monthly water deficits give us approximate values in which months and how much evaporation exceeds precipitation, and that is good few to understand if we need in irrigation or we can avoid it.

Scientists found out that empiric equations which reflect relationships between moisture deficit with actual water discharge by irrigated plants could be used for consumptive water use calculation (if determine ratios that allow to find out relationship between these indexes).
One of most simple relationship is like following:

лveg = 10 * йЙ * д

лveg - irrigation water requirement for the considered crop, m3/ha;
йЙ - empirical coefficient for the crop which depend on species of plant and applied agro-technical measures and on vegetation period duration;
д - summary moisture deficit during vegetation period for the cultivated crop, mm.

Phases of cotton development, starting date of vegetation, starting date for irrigation period, share of physical evaporation (from soil surface) for central climatic zone of Uzbekistan were shown as example at Picture 2.2.

Picture 2.2, Specific features (phases of development) for cotton in central climatic zone of Uzbekistan.

To identify value of Êê ratio scientists carry out long term experiments with various irrigation technologies and compare achieved yields with water consumptions, then compare that with actual moisture deficits. These works provide them (to scientists) lifetime employment because plants varieties, applied agricultural methods, irrigation procedures and also climate (it is not uniform as you know) change over the years… so, that can be studied for a long time, even we can say for never-ending long time. At picture 2.3 we showed results of generalization of information on study for cotton irrigation procedures approximately for 70 years. About 270 tests carried out at more than 13 experiment station of Uzbekistan were included there. This crop was most required for a long time, and most of all investigations were carried out foe it, well, about ten times more than the same for lucerne, wheat and corn!
Let us investigate carefully three diagrams at Picture 2.3. We shall clarify a little about the core of these diagrams. Here, с - is a yield at some plot in frames of this experience, and сЛЮУ - is top yield at the plot, where best condition for water supply was provided during this experience.
All the results compared along the plots for each test, for each investigated year were obtained at the same weather conditions, but value of relationship for irrigation rate to moisture deficit during vegetation period (л/д) for each of the plot was different and the yield should depend only on irrigation water volume. But as we can see from the pictures, yield close to maximal one (с/сЛЮУ = 1) found in various tests when relationship between irrigation rate and moisture deficit fo vegetation period are from 0,15 up to 1,2 i.e. there is difference almost ten times! And we can not understand why it is so, because we specially selected only that results where the same "history" was and only irrigation rates were changed. And this spread of data is almost the same both for close ground water table (GWT) and for deep GWT!
It is also important to note that maximal yields at the selected for analyses trials were not essentially lower than 45 .. 50 hundreds kilograms per hectare and mainly the lowest yields were typical for north regions of Uzbekistan.
Possibly, yield depends not only on the "history" and on volume of delivered irrigation water, but does it also connected with skill of farmers? What do you think about that? Anyway, this wealth of material is waiting for their researchers and assayers…
And we have no way than to orient to "golden mean" of tested "clouds" of data and take the very same ratio by 2.1 formulas. йЙ = л/д = 0,4┘0,65 (smaller values for close GWT, and larger meanings for deep GWT). Nevertheless, it is not bad for orienting. Being aware of deficit for vegetation period from weather data, we can multiply it to Êê factor, and obtain approximate requirement for irrigation water. Total deficit for vegetation period (IV…IX months) is about 1000 mm. Then, irrigation water requirement will be from 400 up to 650 mm, or in terms of m3/ha it will be 4000…6500 m3/ha. About the same amount is necessary for grain maize, but it has declined by a third for grain crops, i.e., 3000…4500 m3/ha. It is necessary to mention that a part of this requirement could be covered by deposit of moisture during non-vegetation period, if it can be saved in soil by correct agricultural methods

Picture 2.3. Actual data on amount of irrigation water used for cotton, which was obtained from tests of different scientists. Data obtained at GWT close to surface were collected on upper picture, data obtained at GWT between close and deep - are on the medium picture, and GWT at lower than 3 m - are on the lowest picture. (Points over с/сЛЮУ = 1 are conventional, they show only number of tests, which were used for evaluation of various relationships between л/д and for graph plotting).

So far we deal with average annual climate records, but all years are different in nature, there are dry years, but there are also rainy years. It is natural, that there is necessity to irrigate in rainy years, but it is necessary to irrigate in dry years. That is why equipment for irrigation will be used only in particular dry years. But sometimes, stability of cropping capacity from year to year can be more important than some extra costs for management of irrigation.
Further on (in Chapter 9) we shall tell you a little about what for else water is consumed at irrigation systems to maintain healthy growth of plants at fields, and you won't find it funny!
Below in Table 3.1 values of Êê for various crops in Uzbekistan were shown as example, that was taken from the work where generalized great experience of scientists of Central Asia (Design values of irrigation water requirements for crops in Syrdarya and Amudarya rivers basins. Authors: V.R. Shreder, V.f. Safonov and others). I take off my hat as a sign of great respect in the memory of great scientist - my edifier V.R. Shreder, who was a guru of this giant work, I intentionally introduced you with the data, which were used during its development, and that was done with the purpose - you are to be doubtingly upon any conclusion that does not belong to you and not trust to anybody's orally told conclusion.

Table 6.1. Values of йЙ factors for various crops in accordance with climatic zones of Uzbekistan.

In accordance with climatic zones

Crop	Ñ-1	Ñ-2	Ö-1	Ö-2	Þ-1	Þ-2
Cotton	-	0,60	0,63	0,65	0,68	0,70
Lucerne and other green food.	0,77	0,81	0,84	0,88	0,92	0,95
Gardens and other plants	0,53	0,55	0,58	0,60	0,62	0,65
Vineyards	0,44	0,46	0,48	0,50	0,52	0,54
Grain maize and sorgho	0,62	0,61	0,62	0,59	0,58	0,57
Cultivated crops with double crops	-	-	0,66	0,69	0,72	0,75
Cucurbits crops	0,35	0,34	0,33	0,33	0,33	0,32
Late cucurbits crops	-	-	0,31	0,31	0,31	0,30
Long term vegetables	0,76	0,79	0,82	0,86	0,89	0,93
Rathe-ripes vegetables and potato with double crops	0,79	0,83	0,86	0,90	0,94	0,97
Late vegetables and potato.	-	-	0,69	0,68	0,67	0,66

Average values of moisture deficits during vegetation period according to climatic zones of even lands of Uzbekistan were shown below in Table 6.2.

Table 6.2. Average values of moisture deficits during vegetation period according to climatic zones of even lands of Uzbekistan (mm).

я-1	я-2	ж-1	ж-2	ч-1	ч-2
900	950	1000	1050	1100	1150

Further on we shall tell you a little about what for else water is spent at irrigation systems to maintain health growth of the plated crops at fields, and "there'll be hell to pay"!

Then we shall address you to experience of the great of soil science and agricultural engineering and we shall think a little together with you how water could be used more efficiently, either the water that is obtained for irrigation, or the water that is abstracted from natural water resources which could be saved by cheep and plain ways. But we shall tell about that a little bit later, after you get more familiar with HER MAJESTRY, FOSTERER OF ALL FLESH ON LAND - SOIL!

 

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