Antonov V.I.

SPRINKLING? THAT MAKES GOOD SENSE...

The article was published in the "Narodnoe slovo" newspaper (Tashkent, Republic of Uzbekistan)

Such an irrigation way like sprinkling is regarded by Uzbekistan farmers, used to irrigate their fields mainly by furrows by means of hacks, with some prejudice; although this irrigation method seems to be borrowed from the nature itself and is, therefore, the most natural way of moisture-charging plants.
Sprinkling was applied in Uzbekistan in 1960-1985 years in the course of the pilot production, but the investigations in that field were not carried to their logical conclusions. Nevertheless, on the basis of those incomplete investigations, an opinion has been formed that even if sprinkling is applicable towards our system, it is so just only on grassland or highly permeable sand soils not subjected to salinization process. They thought, as well, that under our hot and arid climate, at sprinkling, great water loss to evaporation would take place. One should say, such a view (both concerning soils acceptable to sprinkling and water losses) still prevails in "brains" of our many scientists and specialists in land-reclamation.
Meanwhile, the world experience displays that application of sprinkling may be considerably wider, and this method gains more and more ground in other countries throughout the world, including for medium loamy soils being in need of draining and seasonal leaching. More than 60 % of the irrigated zones in Uzbekistan are soils of this sort, and their productive return with the irrigation methods and techniques applied today decreases from year to year. This is particularly evident in the Djizzak and Syrdarya regions, as well as in other regions of the republic.
As for great water losses to evaporation, which, allegedly, accompanies sprinkling, so, correctly conducted experiments show that just the opposite; we shall dwell on this question below.
Let us take a new look at the sprinkling way and a probability of its spreading under Uzbekistan conditions: firstly, taking into account current situation in the irrigated agriculture, and, secondly, from the position of the world experience that have been accumulated.

A folk wisdom says: "It is bad when there is insufficient water, it is even worse when there is excess water". The lessons we are drawing from the experience of irrigation and reclamation of lands in the Golodnaya, Djizzak, and Karshy Steppes, in the Amudarya river lowers and other regions of the republic corroborate this. Large-scale reclamation on new lands for irrigated farming that took place in those regions during 60s to 80s of the last century was carried out when Uzbekisatn did not feel yet water resources deficit. Paces of work were high; water then was delivered in abundance to land tracts being reclaimed, by heavy irrigation rates; everybody was glad at water arrival to virgin lands, which had not enjoyed water for ages, but, at the same time, that caused fast rise of groundwater table and provoked repeated salinization of the irrigated lands.

But, it seemed then that an efficient way of groundwater table rise and salinization control was found, namely drainage and so called leaching irrigation regime.

They began building the drainage systems on all new-reclaimed land tracts; drainage density amounted to 60-80-100 running meters per hectare; and observations showed that those systems seemed to manage desalinization. Indeed, the drainage, while was kept in the state of operability, actively carried salts out of the fields.

Yet, the same observations proved that upon ending vegetation irrigation the soil salinity returned. This phenomenon was named "seasonal salinization", and they began to fight against it by carrying out autumn-winter leaching. At that, the leaching rates were heavy too, they came to 5-7 thousand m3/ha and virtually became equal to the irrigation rates which were supplied to the fields during a vegetation period. Nevertheless, seasonal salinization continued to display itself year in and year out.

Salts amount carried out by the drainage systems already exceeded many times their original reserves in the soil-inhabited layer, nevertheless their concentration in that layer did not decrease in effect. This is explained by the fact that the salt reserves were replenished again in the soil layer thanks to capillary inflow of them from the lower horizons, to which excess of water supplied to the fields penetrated dissolving relict salts those had been accumulated there for previous geological epochs.

An idea has arisen: using vertical drainage holes, to break the capillary band through that, like through a fuse, salts reach up the land surface. But, vertical drainage, at first, can be applied not everywhere and only under corresponding hydro-geological conditions; at second, even where such drainage was used, it was not perceptible good because of, in the main, that submerged pumps installed in the holes failed frequently and were not repaired immediately and efficiently. As a result, constructed vertical drainage systems operated inefficiently, and, at the present, due to jumping in electrical energy prices their operation has been stopped at all.

One should note that meliorative state of the lands reclaimed for irrigated agriculture during 1960s through early 1980s was always unsteady, although water was delivered to the lands in surplus. Yet, as long as the drainage systems built there were operational, on the background of the leaching irrigation regime and autumn-winter leaching, they succeeded in keeping relative meliorative prosperity of those lands, but that was achieved at the cost of increased water supply.

Nowadays, under the conditions of water resources shortage and when most part of the drainage is out of operation and its rehabilitation is quite problematic, we are noticing that, in spite of water supply reduction to fields, at the furrow irrigation used now and conducted soil leaching water loss to filtration, depth water percolation and groundwater replenishment still remain high; and this, under inoperative drainage, promote rapid evolution of both repeated salinization process and drastic aggravation of the irrigated lands' meliorative state as a whole. Just this we confronted, as we mentioned above, in the Syrdarya and Djizzak regions, lands' meliorative state of those was always unsatisfactory, and today, due to failure of the drainage, it is critical.

So, what do we have to do in the present state of affairs? To restore right away tens of thousand kilometers of horizontal subsoil drains and thousands of vertical drainage holes? How much time, efforts and money will this take? Let us suppose we shall restore the high-capacity drainage systems, and then? Will we return to that water-waste technology of regulating water-salt regime of irrigated lands, failure of which we have made sure of? Thus, why to make again the same mistake?

Let us apply logic and consider experience of countries having conditions similar to ours, that is the countries those feel water resources lack and have to solve the repeated salinization problem on irrigated lands. The most experienced in this question is the United States of America, having in view their practice of maintaining irrigated agriculture in short-in-water and arid south and west cotton growing states.
So, purport of water-salt regime control in soil root-inhabited layer and, in general, sense of melioration of lands subjected to salinity under the conditions of these states consists in ensuring wanted optimal regime at modest water amount supplied to the fields; then salts rise to the land surface from the groundwater and their over-carrying from the lower horizons will be minimum. The Americans undeviatingly conduct such a doctrine already for the last decades. In other words, the sense consists in that under the conditions of salted groundwater, one should desalt not its column, but the aeration zone only, namely soil layer from which plants get water.

The Americans succeed in keeping such a regime chiefly owing to using water-saving irrigation methods and perfect irrigation technologies and, in most, thanks to using sprinkling irrigation that became much widespread in the USA.

Many countries in the world today successfully adopt the experience of the Americans, but we do not yet think it out, and it seems like nobody intends to properly improve our irrigation techniques and technology.

Meantime, many farmers in the Syrdarya and Djizzak regions, under the conditions of drainage failure at their sites, began to reject supplying to them high water quantity, it would seem to be as usual; and they seek irrigation of their fields with little rates, reducing the furrow length and more thoroughly controlling irrigation flow distribution over the field. That means the farmers realized by intuition that surplus water under the conditions of salted groundwater and non-operating drainage is bad. But, unfortunately, our scientists did not yet understand this.

However, it is too complicated to distribute uniformly a little irrigation rate over a field at furrow irrigation, or rather it is actually impossible. Whether we want this or not, it is impossible to avoid water loss to depth filtration at furrow heads; and at that field's farther part and single higher places remain under-moistened; as for the moisture-charging uniformity factor of a soil root-inhabited layer over the field area (or, as they call it, the irrigation uniformity factor), it, at such an irrigation, becomes equal to around 0.3, that is to say 70 % of the plants in the field either do not get water at all or do that in a non-optimal regime.

Farmers in a similar situation confront the dilemma: if you over-irrigate the field, it will cause a sudden salinity rise; if you under-irrigate, it will not provide with the required moisture delivery necessary to the plants. And, both in the former and in the latter cases, loss of the considerable crop part is inevitable, that we are observe on the experience of the Syrdarya and Djizzak regions and some other regions of Uzbekistan, meliorative state of which is bad.

It will be possible in fact to avoid the disadvantages stated only in the case if to distribute little irrigation rates over a field by a mechanized manner. In the best way with such a problem can cope only sprinkling machines. The irrigation uniformity factor (at both little and great irrigation rates) under sprinkling irrigation is ensured at the rate of 0.85-0.95. Water loss to depth filtration is, at that, minimum; and, consequently, the heavy drainage that we had built formerly becomes unnecessary. One can do with rather lower drainage capacity, and, therefore, restoring drains non-operating today is required just where it will be needed. In the main, open collectors will handle water distribution task.

Of course, leaching salted lands will be necessary, at that, but such a leaching irrigation will require non-essential water amount, and, generally, that can be combined with pre-sowing moisture-charging, especially as this irrigation will be assigned to desalt only the upper soil layer. At the same time, one can carry out such irrigation by the sprinkling way, as though in addition to natural precipitations, or by furrows. And the part of irrigation rate which, at sprinkling, will be spent to filtration (on the average, this is 10 % of water supply to the fields) will ensure the leaching effect needed in a plant vegetation period.

As to high-salted and heavy clay soils, the approach to them should be special, and we are not talking about them, especially since there is no so much ones in Uzbekistan; the most part is represented by the sierozem soil formed on mean-loamy grounds.

All the stated above sufficiently clearly point, in our opinion, to that we must change the technical policy in the question of irrigated lands' water-salt regime control.

Yet, let us recur to the American experience. They think the second using return flow for irrigation, that is a mixture of waste and mineralized waters, will carry to an absurdity. Indeed, at that, it turns out that the salts carried with the drainage water off the fields of one land tract further, at the second using this water for irrigation, is brought in fields of a neighbor or downstream land tract. And this happens repeatedly, from the river basin's headstreams down to its lower streams, where often reaches water already practically unusable for irrigation. Is not this an absurdity? That is why the Americans try to reduce to the minimum amount of collector-drainage effluent formed in the irrigation course, and they draw it aside, outside of the irrigated land tracts and beyond the bounds of possible returning to water sources, so that to ensure water quality keeping in them.

In Uzbekistan, with the existing total water off-take quantity for irrigation of 52-56 km3, about 20-23 km3 of return flow is formed, out of which 13-15 km3 (or near 70 %) is used for irrigation. It ensues that we irrigate the considerable part of our fields with salted and contaminated-with-various-pesticides water. Such a big quantity of forming and using return water has a sharp effect on water sources and ecology of the republic as a whole. That is why the paramount task of ours is reduction of this quantity as much as possible; this can be gained owing to using water-saving irrigation methods and perfect irrigation technologies.

Right this issue should be tackled today in Uzbekistan first of all, especially as this will not take a big investment amount. Sure, we cannot completely exclude repeated use of return water for irrigation and this not allowable under the present water resources deficit, however, if we reduce return flow amount being formed at least by half, that would be a great achievement.

In connection with the stated, along with improvement of the traditional and usual for local farmers techniques and technologies of surface irrigation by furrows, strias and checks using for that means of small mechanization, the most serious attention has to be paid to the issue of transition to sprinkling irrigation method.

Some time we had certain production irrigation experience in sprinkling irrigation under Uzbekistan conditions, we said that in the article's beginning, and that experience showed itself good in the whole. Researchers Petrov, Demidov, Moskaltsov, Peresypkin, Morozov, Ivanov, Sevryughin, and other scientists carried out investigations on possibilities for wide sprinkling application in Uzbekistan. In 1975-1985 years, there were 585 units of various sprinkling machine types in the republic, and the total area irrigated by those came to 12 thousand ha, but sprinkling did not get expected wide employment; the main obstacles to that were:
- inactivity and psychological unreadiness of our farmers accustomed, mainly, to hand labor with a hack, and therefore their aversion to such a novelty as sprinkling (by the way, such an aversion and dislike were shown relating to tractors in the early 30s of the last century);
- insufficient popularization of that irrigation way and non-arranged training specialists in machine-operation for mass exploitation of sprinkling facilities;
- aversion to measures for forming in the republic a proper material and technical basis for repair engineering and maintenance of the sprinkling facilities;
- reluctance to organize own industrial manufacture of such a facility.

At the same time, in the independent states as Russia, Ukraine, Byelorussia, and Moldova the obstacles stated above were surmounted, and sprinkling irrigation way got there the widest application and continues to extend. Thus, in Russia, 50 % of the areas are irrigated by sprinkling; in Ukraine and Byelorussia - 80 %; in Moldova - 90 %. Last years, sprinkling is actively applied in Kazakhstan, Kirghizia, and Transcaucasian states, not to mention farther foreign countries. In Uzbekistan, in effect, nothing is done in this respect.

They may have a protest with me that in the countries listed the climate is not so hot and arid as in Uzbekistan and that water losses to evaporation from the raindrops during their flight in the air there is much less than in ours, and consequently, sprinkling use is justified there. Well, I have to say concerning this that studies, performed bona fide, show that under sprinkling, over a field surface, specific microclimate is formed fast and keeps for a sufficiently long time. That reduces both general moisture evaporation out of the air and soil, and transpiration of it by plants, and in the result, water loss proves to be very low in the whole. As to moisture loss out of the drops in the air, they amount to about 3-4 %, at first, and for the next 5-6 minutes decrease to 1 %.

According to the developmental works of the "Vodproject" Association, nowadays, 1700 thousand ha of lands are in need of reconstruction of irrigation systems, and 900 thousand ha of lands require meliorative improvement. "Vodproject" suggests, in the first place and urgently, execution of the mentioned actions on at least area of 690 thousand ha, this is 16 % of the total irrigated area of the republic (in the main, this refers to the Syrdarya, Djizzak, Kashkadarya, Bukhara, and Khorezm regions).

So, let us consider carrying out of these works from the standpoint stated above and, in combination of the reconstruction and reclamation actions, we will use sprinkling for these lands. Preliminarily, let us during three years (2004-2006) conduct a experimental-productive test of the approach offered for these works execution on pilot sites located under conditions specific for the pointed regions. Such a test will make clear many things, and then we will act more certain.

According to the pre-designs of the "Vodproject" Association, it turns out that one conventional sprinkling machine with water supply capacity of 100 l/s under Uzbekistan conditions is supposed to irrigate for a season, at three-shift operation, at average 100 ha. Three-shift operation of machines is required to exclude night water discharge from the irrigation canals system. To serve an area of 690 thousand ha, we will need (on the safe side a little) 7 thousand units of conventional sprinkling machines. Conversion of one land hectare with furrow irrigation to sprinkling irrigation, allowing for reconstruction of the irrigation network, its adaptation to operation with sprinkling machines, and purchase of sprinkling equipment, will amount to about 800 US dollars. Thus, the program of land conversion of 690 thousand ha to sprinkling will cost approximately 550 mln. US dollars.

If such a program will be realized during 10-15 years, then, it will be required to be assigned to these purposes in 35-55 mln. US dollars per annum.

This is, as they say, at the start. And, generally, Uzbekistan will need to attend to establishment of its own manufacture of sprinkling equipments, especially because there is nothing complex in this, and establishment of enterprises for their servicing too. At that, we should direct our attention to manufacture simple in operation and mobile sprinkling machines, most fit to the mass use in small and mean-sized farms, which become more and more popular in the republic.

Of course, to realize the program suggested, it will require serious support of Government and overseas partners. As such partners, the American firm "Wallmount", considering development in the sprinkling sphere; German firm "Baleh"; and the joint-stock company "Kherson combines" of Ukraine, which arrange full-scale manufacture of sprinkling machines DFD-80 (incidentally, made and patented in Uzbekistan) can be attracted. This sprinkling machine has obtained wide recognition in Ukraine and well competes with American-type-machines.

Costs to purchase by Uzbekistan of the sprinkling facility and current costs to its maintenance must be rapidly repaid, and in the main thanks to increase of crop capacity. Preliminary calculations showed the payback term of start investments at land conversion to sprinkling irrigation under Uzbekistan conditions will be two years, and the world experience of countries where sprinkling irrigation is developed testifies this. However, this can be verified in the course of experimental-productive studies on pilot sites. And when Uzbekistan establishes series manufacture of own sprinkling equipment, economical indices of its application are supposed to be still higher. There is an opinion that using sprinkling will increase the prime cost of crop production. But, this is wrong, since crop rise will cover with interest costs related to the sprinkling facility use.

The effect will be got, as well, in the substantial reduction (equal to water loss quantity on fields at irrigation ways applied today) in water-offtake amount from water sources, water delivery by canal systems, and, the essential thing, in cost decrease engine lifting surplus water amount by pump stations. The latter is too important, if to take into consideration that 40 % of water supplied to irrigation in the republic is raised by pumps, and electrical energy charges consumed by them are very high.

But, saying about the expected effect, one should, at the same time, remember that conversion to sprinkling irrigation in the republic will not increase the total usable water resources amount. One should expect, mainly and first of all, ecological efficiency that will be expressed in great reduction of return flow being formed with all its adverse consequences (this is quite urgent for Uzbekistan), and, of course, in improvement of irrigated lands' meliorative state and their production output rise, that is no less topical too. Moreover, due to actual water saving achieved, they can develop additional areas for irrigation.

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