RESULT OF SUBSOIL IRRIGATION RESEARCH OF ALFALFA GROWN FOR GREEN FEED IN VOLGO-AKHTUBINSKAYA FLOOD PLANT

Relevance of subsoil irrigation usage for growing feed crops on alluvial meadow soils is shown. Distribution of pjezometric pressure, along the water emitter line during the irrigating period, is analyzed. Formation of moisture patterns in the soil regarding the quantities of irrigating water and emitters design are considered. In order to define the characteristics of moisture patterns in the soil, depending on the quantities of irrigating water, the ratios of vertical water spreading K v and forms K f are calculated. Expediency of usage low irrigating rates is substantiated. As a result of research, mathematical relations were derived in order to define water outlays in the emitters made of pottery tubes with diameter 50 mm under water pressure at the line 0.1...0.7 m. It is determined that usage of subsoil irrigation allows increase of commercial crop harvest, significantly save water resources, labour and energy comparing to sprinkling. I n t r o d u c t i o n For increase of irrigated land efficiency, the choice of ecologically safe technology and technological means for watering in view of irrigation water economy has got the great importance during the last years. The leading countries of the world prefer such ways of watering which allow adjustment of water-submission according to water consumption of agricultural crops. In practice all local irrigation methods meet these requirements including subsoil irrigation (SSI). Using of the given irrigation method allows to create optimum water-air regime 1 Askar Ahmedov, PhD, assistant professor at the chair of Technologies in management of natural resources at Ecology – Land Reclamation Department of Volgograd State Agriculture Academy. 400002. Universitetsky prospect, 26. Volgograd, Russia. Tel. (8442) 41-98-28


I n t r o d u c t i o n
For increase of irrigated land efficiency, the choice of ecologically safe technology and technological means for watering in view of irrigation water economy has got the great importance during the last years.The leading countries of the world prefer such ways of watering which allow adjustment of water-submission according to water consumption of agricultural crops.In practice all local irrigation methods meet these requirements including subsoil irrigation (SSI).Using of the given irrigation method allows to create optimum water-air regime of soil, to keep its structure and to improve aeration, to provide optimum for plants capillary humidification of soil.As a result the crop capacity of agricultural crops increases in 20-30 % in comparison with sprinkler irrigation.
However opportunities of the subsoil irrigation are not completely realized because of the insufficient studying level of watering theoretical bases and technologies.In this connection there was a necessity of carrying out the research lines, directed on the development of the alfalfa subsoil irrigation technology for the green forage in Volga-Akhtubinskaya flood plant.
By virtue of geographical conditions the flood plant climate is sharply continental and droughty.The mid-annual temperature of air is about 8°C.The volume of precipitation is 300 -350 mm.During the warm period (from April till October) it falls about 2/3 of precipitation.On the average, the evaporation is estimated to 900-1000 mm.
In the geo-morphological relation, the plot is in the sub-zone of alluvial meadow complex lightly loamy soils.The content of the humus is low.The average is 0,86 -0,88 % of the dry soil in the 0 -0,5 m layer.On the plot with the sprinkler irrigation, the density has made 1,44 t/m, and at the SSI -1,50 t/m for meter ground layer.The least moisture capacity is accordingly 19,31% and 19,27 % of the dry soil weight.The soils are not saline.In view of the soil mechanical structure and filtration properties for maintenance of the optimum of humidification regime are stipulated by minimal pipes installation depth of the subsoil irrigation -0,5 m and measures on prevention of irrigation water leakage in the lower layers of the soil structure.With this end of view under the humidificator, it is arranged the un-filtration polyethylene screen in width 0,25 -0,30 m.The screen above the humidificator is arranged for the prevention of the ooze mud and increase in distance between humidificators at the expense of the increase in a contour of humidification.

Studying
On the experimental plot of the subsoil irrigation in the conditions approached to industrial, two constructions of humidificators produced from potter's pipes with internal diameter of 50 mm and length of 333 mm have been investigated.In the first construction the pipes are connected with the polyethylene clutches of the 0,1 m width, distance between humidificators is 2,0.In the second construction the pipes are laid closely to each other, their joints are not isolated, distance between humidificators is 1,5 and 2,0 m.
All humidificators are produced with the length of 125 m.A bias of the humidificators is 0,002.
Detailed and deep studying of the raising questions were carried out by following supervision and accounts: density of ground -with the method of cutting rings (under K a c h i n s k i y ); density of the hard phases of the soil -with the picnometrical method; humidity -with the weight method; the porosity and the full moisture capacity-with the calculation method; the least moisture capacity -with the flooding method.
The account of productivity was determined with the method of registration platforms (4-5 m 2 ), in quadruple frequency.Mathematical data processing was carried out with the help of correlation and dispersive analyses on the computer, with the help of applied programs on mathematical statistics.
Dynamics of humidity in the field conditions was studied on the special water-balance platforms located at diagonal of the allotment on distance of 20 m from the head, in the middle and 20 m at the end of the humidificator.Humidity tests in cross-section between the humidificators were taken above the humidificator through every 0,2 m and in the middle between the humidificators by variants.Humidity tests on a vertical were selected through 0,1 m on depth up to 1 m in quadruple frequency up to, and after the watering , in day or two.
The value of the irrigation norm was calculated under the formula of academician A.N.K o s t j a k o v a (1960) in view of the factor which is taking into account the character of distribution of water in ground: where -m is the irrigation norm, m/ha; ¿ -the factor, which is taking into account the water distribution character in the soil, coming from the humidificators, changes in limits from 0,4 up to 0,7 depending on the mechanical structure of the soil and on the distance between the humidificators; H -capacity of the calculation soil layer (H = 0,8 m); β hb -humidity of the calculation soil layer, HB ; β hthe soil humidity on the plot before the watering, % ; γ o -the soil density, t/m 3 .

Results
Efficiency of the subsoil irrigation systems is in direct dependence on the correct establishment of the watering technical parameters, on the distances between the subsoil humidificators and the depth of their laying, optimization of the irrigation norms, of the water absorption speed, of the length of the subsoil humidificators.The analysis of the researches of various authors and also our own researches has allowed to draw a conclusion, that in all cases the distance between humidificators for the continuous sowing cultures should be appointed from the close contours conditions of the humidification and to coordinate with the soil capillary properties.
The quantity of the evaporating water at the subsoil irrigation is minimally, but the filtration losses, especial in homogeneous soils, can be significant.Besides the humidificators' construction, their size is in direct dependence on the size of the piezometrical pressure above an axis of the humidificator and the regime of the soil humidity.
By the studying of the piezometrical pressure on the humidificators length, the seven piezometers have been established in the following order.The first is in 2,5 m from the head of the humidificator, the last is on the same distance from the end-part of the humidificator.The basic parts were laid through every 20 m from the head of the humidificator.The size of the piezometrical pressures was measured from the humidificator axis, including piezometer in the pressure head tank, the counting out the piezometers undertook every 10 minutes, and then -30 minutes, up to the constant value.
By the analysis of the average humidity dynamics in the soil it is necessary to note non-uniformity of its distribution on the length of the humidificator.At the almost identical pre-irrigation soil humidity in the layer 0 -0,8 m on the humidificator length, the soil humidity, after the watering termination, decreases up to 5-th section and then increases up to the end-part.At distance of 0,25 m from the humidificator axis in the 5-th section this value in comparison with the 1st section decreases on 8,7 %, but at the humidificator end on 1,9 %.During the time the moisture redistribution is observed in peripheral horizons of the humidificators.The distribution character remains unchanged: the greatest values of the soil humidity are in the head and in the end-part of the humidificator, the least are in the middle part.During the 1,3,5,7 days after the watering the humidity continues to decrease, reaching the almost pre-irrigation values at the last supervision.As it is known, in this case the moisture possesses the greatest mobility.Regular measurements have shown, that the basic amount of irrigation water is accumulated in the soil layer of 0 -0,8 m and 22,5 % gets in the arable horizon, 72 % in the layer of 0,3 -0,6 m, and only 5,5% is infiltrated.
The further supervision for the soil humidity after the watering shows that the character of moisture distribution in the soil horizons on the length of humidificator is ambiguous during the time after the watering termination.Comparing with graphic dependences of the average dynamics of soil humidity on the length of the humidificator, it is necessary to note concurrences of the form of curves for the same chinks sections.
The difference in the absolute marks of humidity, depending on the arrangement of the chinks sections on the humidificator length, coincides on character with the dynamics of the piezometrical pressure.
The quality of the soil humidification in many respects depends on the water distribution uniformity at all tubular humidificators.Non-observance of this condition by designing of the subsoil irrigation systems causes the fluctuations of the piezometrical pressures along the length of the humidificator.Hence, the irregularity of the soil humidification along the length of the humidificator causes instability of the agricultural crops.
Studying of the contour formation questions depending on the humidificator design, on the way of the irrigation water submission into the ground, on the irrigation norm and the pressure was carried out in the laboratory -irrigation instal-lation.It operated by following: a water-pressure head tank -a pressure regulator -a researched humidificator.The processing of the cameral materials by field researches was undertaken with the help of usual receptions of mathematical statistics.The size of researched pressures did not exceed 0,2 -0,7 m.
Let's consider results of experiences.In the 1st type of the construction the form of the moistened humidification contour comes nearer to rectangular or round, a little extending in the lower part of the contour, laying under the humidificator that is caused by the entering of moisture first upwards and in the asides, then downwards.
The sizes and the areas of the humidification contours are given in the scheme 1 depending on the design features of the humidificators and the value of the pressure.From the scheme it is clear, that on the average area of the moistened contour in the 2nd type of the humidificator design is at 0,04 -0,08 m or more, than in 1st.

Tab. 1. -The humidity contour dimensions (a -after watering, b -in 18 hours)
In the 2nd type of construction, the form of the moistened contour comes nearer to an ellipse that is caused by the entering of moisture first in the asides and then upwards and downwards.At the pressure increased from 0,7 m and more, the area of humidification increases insignificantly, nearly 0,05 -0,07 m in the horizontal direction, but here is danger of the soil suffusion and the water outgoing on soil surface.Hence, it is expedient to apply the un-filtration screen.
Screens allow to increase distance between the humidificators and to come up to 1,4 -1,5 m, and besides that the application of screen allows increasing of the area of the moistened contour in 1,3 -1,7 times.Thus the optimal is pressure of 0,5 -0,6 m.
For the studying of the irrigation norm influence on the contours formation of the humidification the watering norms of 600 and 350 m 3 /ha are considered.
For the definition of the humidification contours characteristic depending on the irrigation norms were counted up by all factors of vertical distribution b and forms of f .Factor b estimates the optimality of the humidification contour, i.e. this values attitude of the contour humidification distribution upwards (a 1 ) and downwards ( 2 ) from the axis of the humidificator, and f -the attitude of the height of the humidification contour D B to width D r .Hence, at the increase of K b the irrigating water losses for the filtration are decreased and reduction of the value K f allows to increase distances between the humidificators.The values of the factors b and K f are calculated by us and are given in the scheme 2. Studying of water expense depending on the subsoil humidificator was carried out on the experimental -field installation.The potter's pipes humidificators were tested at the water pressures in the head from 0,10 up to 0,70 m.During experience the constant water pressure in the head of the humidificator was supported.The control was carried out with the help of piezometers.The water expense value was fixed through every 10 minutes from the beginning of supervision.Tests were carried out at the pre-irrigation humidity of soil 75 -80 %HB.

Tab. 2. -The influence of watering norms value on the humidification contour distribution
With increase of pressures the water expense in the head of the last was increased.So, at the pressure of 0,1 m the water expense after 10 minutes of work was 0,30 l/s, at the pressure of 0,30 m -0,51, 0,5 m -0,645 and 0,7 m -0,790 l/s, i.e. at the increase of the pressure to 0,6 m the expense has increased in 2,63 times.
Experimental dependences q = f (t) were approximated with the help of the equation q = a (b + t) c + d, where q is the water expense in the humidificator,l/s; t -time from the beginning of watering, minutes; c-power index equal-1; a, b, d -factors, which numerical values are experimental determined.For our conditions curves q = f (t) are described by the following equations: q = 6,55 T-1 + 0,22 at the pressure of 0,7 m; q = 5,89 T-1 + 0,15 at the pressure of 0,5 m; q = 4,65 T-1 + 0,11 at the pressure of 0,3 m; q = 3,21 T-1 + 0,04 at the pressure of 0,1 m.
At the reduction of the pressure the water expense in the humidificator head decreases.At t → ∞ there comes full stabilization of water expense, and at t → 0, according the equations, q → ∞ , but does not exceed limiting absorption ability of the pipe.
The analysis of the received data shows (fig.1), that in all cases the points in the chosen scale are laid approximately on the direct line type y= ax+ b.Empirical formulas are selected with the help of the leveled points method.The received dependences with sufficient accuracy are proved by the checking of some points on straightforwardness at each variant.The more is absorption ability of the pipe -humidificator at identical biases, the higher the straight line is laid.

Fig. 1. -Dependence of the water expense in dampeners from a pressure during having watered
General received equation and considering, that dependence of the given humidificator expense on time has hyperbolic character; we shall conclude the common equation connecting the specific time from the watering beginning and the pressure in the head of the dampener: Q = 0,0031+4,5080 -0,967 The mean-quadratic calculating expense of deviation from actual at the considered pressures during all watering changes within the limits of 0,36 -4,18 %.The scope of the received dependences is limited at pressure (H= 0,1 -0,7 m) and on the time (T = 10 -340 minutes) to appearance of the established expenses.
Using calculating dependences it is possible to count up supply of irrigated water for any time interval and at various pressures, to do interpolation, extrapolation and to define the calculating expenses of water in the humidificator.
During researches on the experimental plot of the alfalfa on a green feed "Sinskaya" was cultivated.It was sowed in the pure state, the method of sowing was ordinary, the technology of alfalfa cultivation on a green feed was standard for the given region.The regime of the irrigation was studied on the example of the alfalfa of the second and third year of the life by different ways of watering.
At all methods the greatest crop of alfalfa green mass was provided in the second year of life, and for the third year its efficiency has sharply decreased, due to thin out the plants.Within the limits of each year minimally high crop of alfalfa was formed in the first hay crop and was 28 -35 % from the sum for a year.It was promoted by favorable temperature conditions and the longest period of its increase.A crop in the further hay harvest goes down, it can be explained that by the repeated mowing of alfalfa the supply of plastic substances in root neck is exhausted by the end of vegetation.Only in the second and third year of the life efficiency of the fourth hay crop was a little bit higher, than of the third.It is explained to more lengthened vegetation period of the fourth hay crop.
At the sprinkler irrigation in the second year during 4 hay crops has been received the maximal productivity of 87,0 t/ha.On the average, at the sprinkler irrigation for two years productivity has made 79,4 t/ha.Application of SSI in comparison with sprinkler irrigation (DDA-100 MA) allows increase of the alfalfa productivity.The greatest crop (95,0 t/ha) has been received on the plot with the highest pre-irrigation soil humidity (80 % LH), it is on 8,0 t/ha more, than by sprinkler irrigation.
Decrease in pre-irrigation humidity of ground to a level of 70 % LH (LH -Lowest water holding capacity) on the average reduces the alfalfa productivity on 12 -19 %.The further reduction of readily available moisture even more reduces the alfalfa productivity.
Crop reduction is marked by increase of distance between humidificators.So, at the increase of distance between humidificators from 1,5 up to 2,0 m, on the average, productivity is reduced on 6,2 -12,1 %.
The design of humidificator influenced on the formation of alfalfa crop.So, at distance of 2,0 m between humidificators, productivity of the alfalfa on green feed is more on variant, where humidificators from potter's pipes with anti-filtration screen are down and up, than with anti-filtration screen on the free lying clutches, on the average in 5,1 t/ha.Dynamics of average mowing alfalfa crop, depending on different watering ways is shown on fig. 2.

Fig. 2. -Dependence hay crop average productivity of Lucerne on green weight
From the analysis of calculations it is possible to note, that subsoil watering is a highly effective way of an irrigation which application gives substantial growth of the alfalfa productivity on green feed.Among considered variants of the subsoil irrigation the variant at which humidificators are made from potter's pipes in diameter of 50 mm with antifiltration screen up and down, and distance 1,5 m between humiidificators is optimum.The calculations according to bio-energy efficiency of alfalfa cultivation in Volga-Akhtubinskaya flood plant, at various watering ways, have shown that all variants of the researches are energy saving because the relation of the energy which has been saved up in the biomass of crops, spent cumulative energy in all cases exceeds one (tab.3).From tab. 3 is clear that on the alfalfa crops in the second year of a life the factor of energy efficiency changed from 2,53 up to 2,82.

Tab. 3. -Energy estimation of alfalfa cultivation with help of tests variants
Thus, among investigated watering ways of alfalfa by tests variants the highest bio-energy efficiency has SSI at maintenance of pre-irrigation humidity gorge in 80 % LH.Thus the factor of energy efficiency makes 2,77 -2,82.

D i s c u s s i o n
Now in conditions of growing deficiency of fresh water, as primary, plan is rational use of water resources, practical use of irrigation in resources-saving technologies and the most effective economic ways of irrigation.
The most actual from all the offered methods in present time is application of subsoil irrigation.The particularity of the subsoil irrigation is that movement of moisture in ground occurs not from top to down as at other ways of irrigation, but in radial directions from an axis of a humidificator, basically from below upwards -due to ascending movement of a moisture.Use of given irrigation way allows creation of optimum water-air soil regime, keeping its structure and aeration's improvement, to provide optimum for plants capillary humidification of soil.In this case, the soil blanket has the low humidity therefore the deep-rooted weeds perish, and water stocks in the soil, protected from evaporation, get uniformity and stability.Hence, amount of the water supplied to crop irrigation is reduced.The basic water stocks are concentrated in rooting layer of ground and are rather easily regulated.
The subsoil irrigation is expedient for introducing in wide scales in steppes, semi-deserts and deserts where is sharp deficiency of water; in mountains and the foothill areas subjected to irrigational erosion; on the grounds around of cities; at the comfortable settlements; large cattle-breeding complexes where it is possible to use economic -domestic and lightning cattle-breeding runoff.By this method there is no danger of environmental pollution by runoffs and growing production, ground and air by pathogenic microorganisms and helmints' eggs.Efficiency of SSI is in dependence on the correct parameters of the watering technology -distances between subsoil humidificators and depths of their stacking, optimization of irrigation norms, speed of water absorption, lengths of subsoil humidificators, and hydraulic calculation of humidificators and tubular sprinklers is made on the established water expense.
The subsoil irrigation opens the big opportunities in automation of water delivery process to the soil at simultaneous satisfaction of physiological need of plants in water during all vegetative period.Labour productivity will accordingly be raised at the general decrease in labour expenses.
The subsoil irrigation does not demand additional energy, as it takes place at the sprinkling irrigation, requires scarce materials, such as metal much less and at the same time provides high efficiency of work.
However, despite of a contemplated intensification of scientific researches, of successfully realized projects of land-improvement systems with subsoil irrigation, there are still a lot of unsolved questions which can impede the further increase of the areas with this, undoubtedly, progressive and ecologically safe watering way.

C o n c l u s i o n
It is established, that distribution of moisture after watering and form of humidification contours at subsoil irrigation are determined, first of all, by waterphysical properties of soil, designs of humidificators and hydraulic regime of their work.
The irrigation norms have big positive influence on quality of the soil layer humidification.At the watering with big (600 m/ha) norms of irrigation water sinks on the bigger depth, than with small norms.However, small irrigation norms create more uniform humidification on all soil profile.
For definition of water expense in the humidificator head and the specific expense of water in humidificators, depending on a head pressure and water duration, the mathematical dependences are resulted, allowing to count up supplying of irrigating water for any interval at various pressures.
Giving results have allowed establishing, annual economic benefit at the subsoil watering is received due to decrease in expenses of energy in about 1000 MDg/ha, in comparison with sprinkler irrigation.Energy factor at the SSI has made 2,50 -2,82.
5. Using of SSI systems for watering of alfalfa on green feed in conditions of alluvial, lightly loams allows increase of this crop productivity on 11 -15 % at lower work expenses and economy of irrigating water on 10 -13 % in comparison with sprinkling irrigation (DDA-100 MA).

R E F E R E N C E S
of SSI systems and regime of alfalfa irrigation on the green feed in comparison with sprinkler irrigation were carried out by B.A. D o s p e h o v a ' s (1979), G.V. Ve d e n j a p i n a (1973), V.N.P e r e g u d o v a (1970).