Irrigation technique
Continuous stream irrigation
Fixed-flow-rate irrigation by furrows is still widespread and approximate relation between the discharge to the furrow, length of the furrow and duration of water application are determined depending on furrow slope gradient and soil permeability. With steep slope, the discharge to the furrow will reduce and the furrow length will decrease, as well as the duration of water application will shorten. On gentle-sloped fields, discharges into the furrows is raised, the furrow length is increased depending on soil permeability: the lower soil permeability, the longer the furrows. However, the actual efficiency of this irrigation method is rather low. This is caused by the several following factors:
- Incorrect estimation of discharges into the furrows, furrow length, duration of water application, as well as use of irrigation techniques that are not suitable for the actual field conditions;
- Unsatisfactory quality of leveling;
- Lower level of competence of irrigators and watering quality.
In addition, dramatic changes in the quality of irrigation management have taken place. A large number of farms have arisen, the irrigated land plots of which cannot be provided with water at fixed flow rate because of low water discharge. In this case, a farm is supplied with water at certain time periods at the rate considerably higher than the product of water duty and the irrigated area. According to the data of researches by SANIIRI, under these conditions optimum combination of irrigation technique elements is advised, which would provide high efficiency of the irrigation technique.
The same irrigation technique parameters are recommended for large farms the irrigated areas of which allow supplying water at a fixed rate, because the efficiency of the irrigation technique in this case is higher than with longer furrows.
However, in large highly mechanized farms using as long furrows as possible may sometimes be reasonable with high efficiency of irrigation technique.
It is obvious that irrigation parameters for shorter furrows are characterized by higher efficiency of watering. When local conditions do not allow applying recommended furrow length, the following method is used:
2. Required quantity of reduction of the discharge to the furrow q1 (l/s) and shortening of the duration of water application Ò1 (hour) relative to the standard discharge qs and duration of water application Òs are calculated by the following formulas:
If there is a need to lower irrigation rates W1 relative to standard irrigation rates with a specified furrow length:
1) relative reduction of water application is to be calculated.
2) required discharge to the furrow q1 of water application Ò1 is to be determined as follows:
The design efficiency of water application with recommended irrigation technique parameters is much higher than the efficiency of water application under production conditions.
The major drawback of fixed-flow-rate irrigation by furrows is uneven watering along the furrows because the head and end parts of the furrows become wet at different times and thereto related deep percolation losses take place.
In medium and steep-slope zones, furrow irrigation without surface water escape is impossible. At the average, in this case water escape accounts for about 20-25%. The time of water stream travel in the furrows till their ends even under uniform distribution of the flow at the furrow heads, may vary within a wide range. This is due to the effect of the field microrelief and variability of soils’ water and physical properties as well as the particularities of mechanized treatment of soil. In the furrows through which tractor’s rare wheels passed twice (25%), water stream travels to the furrow end by far more quickly than in the furrows through which tractor wheels did not pass (50%). In the furrows through which where tractor’s fore wheels passed (25%), the water travel speed is also different. This causes considerable increase in unproductive water losses. That is why even in systems with sufficient water supply and with recommended elements of fixed-flow-rate irrigation technique, independent control of the irrigating stream is advisable. The irrigator going along the lower part of irrigation furrows gives signals to the irrigator at the head of the field as to at the head of which furrow water flow should be reduced or increased.
With fixed-flow-rate irrigation, surface water discharge is indispensable at steep and medium slopes, especially on low-permeable soils. The tail water should be accumulated at the end of the field and then directed to an irrigation ditch or downstream irrigated plots. All the waste waters cannot be used for a variety of reasons and are directed to the collector & drainage network. Mixed water of the collector & drainage network should be reused for irrigation of other irrigated plots. This will considerably raise the efficiency of irrigation water use.
Source: Recommendations for optimum compromise of furrow
irrigation elements for different conditions of the Fergana Valley /
Abirov, A.A., Nasonov, V.G. SANIIRI, Tashkent, 2010 [in Russian]
Variable stream irrigation
Intermittent-flow irrigation is a promising practice of surface irrigation. Reduction of irrigation streams to furrows enables saving irrigation water in comparison with fixed-flow-rate irrigation and ensures uniform distribution of water along the length of furrows.
With intermittent-flow irrigation, regulation of water discharge to furrows is carried out making allowance for minimizing water escape from irrigation furrows.
Water is supplied to through furrows at fixed or intermittent flow rate. With intermittent flow, better conditions are created for uniform watering along the entire length of the furrow, water escape is prevented. Usually the space between furrows, their length and depth are determined in the course of test water applications. At the same time, required of water application duration is also determined in conformity with soil moistening. In 1-2 days after water application, when the moisture in the soil becomes redistributed, the following is to be determined: value of moisture spreading in the horizontal and vertical directions; degree of moistening uniformity; degree of interlocking of adjacent furrows. For this purpose, moisture sampling is carried out by using a sampler at some points between the furrows. This is advisable to do at the head, middle and end of the furrow. Also, a trench can be dug with spade across the furrows. On vertical wall of the trench, the contour of moistening will be clearly visible. If there is an insufficiently moistened place between the irrigation furrows, the space between them is shortened or water supply to the furrows is increased (filling of furrows). This method is used at irrigation of fruit trees, berry bushes (currant bushes, gooseberry bushes), wild strawberry. In the spaces between the tree rows in an apple orchard, 4-8 furrows are cut, and 2-4 furrows between berry bushes.
Source: BASARABIA
Uniform moistening of soil along the furrow length can be provided by intermittent-flow irrigation. This irrigation method consists in that at first water is provided at maximum acceptable flow rate for fast flooding of the furrow, and then it is reduced twice. The depth of soil moisture at the head and end of the furrow with such water regulation is approximately equal.
Field watering by intermittent flow can be easily carried out by distributing water to irrigation furrows with siphons. For this purpose, at first an irrigator installs two siphons in every furrow, and when water stream runs to the end of the furrow, he removes one siphon (the discharge is halved).
Irrigation of cultivated crops is carried out by the furrows cut in the middle of the spaces between rows. When irrigating vegetable, there are several options for location of crops relative to irrigation furrows: on the side slopes, ridges, and bottom of the furrow.
When crops are planted on the side slope of the furrow, they immediately get into favorable conditions in terms of moisture. Water application is carried out after planting. At that, the acclimation rate is high – 98%.
Source: Mse-Online.Ru
Unproductive irrigation water consumption for surface water escape as well as the losses to deep percolation at irrigation can be substantially reduced with watering by intermittent flow. This irrigation method allows more uniform moistening along the furrow length and considerably raising the efficiency of irrigation technique. The initial discharge to the furrow should be as high as possible, being confined to the condition that erosion is unacceptable and depending on furrow carrying capacity.
When water travels to the furrow end, the discharge at the furrow head is reduced by a third or by a half, which excludes water escape or decreases it dramatically. This requires reduction of the head discharge to the furrows by several times. At intermittent-flow irrigation, observation over the discharge at the furrow end section should be carried out at the field’s lower part and the irrigator at the head part of the field is to be signaled about the necessity the change the stream discharge at the furrow head. Accurate and fast reduction of water escape under working conditions can be ensured by training irrigators and imparting discharge changing skills to them.
Intermittent-flow irrigation will provide not only reduction of irrigation water consumption, but also rise in crop yield thanks to stopping of carryover of the topsoil outside the field and wash-out of mineral fertilizers.
The following combination of irrigation technique elements at intermittent-flow discharge are recommended for characteristic conditions.
When an irrigation system is sufficiently provided with water and there in no problem with irrigators, it is reasonable to apply another option of regulation of intermittent flow. When in a half or 3/4 of the furrows flow comes to their end part, water escape starts; at that, head discharge to the furrows should be reduced by 50%. With this option of regulation, there is no need for individual decrease of discharge in every furrow; it is enough to reduce discharge to field (auxiliary) ditches or to ok-aryks (irrigation ditches) depending on the scheme of a given irrigated plot.
However, the discharge of irrigating stream can be easily changed during water supply to furrows by means of siphons. Every furrow is equipped with two siphons for supply of scheduled discharges. In case of need to halve the discharge, one siphon is removed.
Source: Recommendations for optimum compromise of furrow
irrigation elements for different conditions of the Fergana Valley /
Abirov, A.A., Nasonov, V.G. SANIIRI, Tashkent, 2010 [in Russian]
Discrete irrigation
The essence of discrete irrigation by furrows (discrete adjustment of water supply to furrows) consists in that the maximum discharge in terms of erosion features of the soil that forms the furrow bed is supplied by pulse trains alternating with pauses. The pulse during which water is supplied is interrupted with a pause. This process will go on until the end of water travel, i.e. until the stream forehead has reached the end of the furrow. Water application culminates with the stage of "additional moistening" during which the furrows are as a rule supplied with halved discharge.
During the pauses, the furrow bed dries up, mudding the pores between ground particles takes place; this leads to decline in deep percolation outside the root zone and smoothing of the diagram/ of moisture distribution along the furrow.
The technology of discrete water supply regulation adjustment is recommended for predominant application at irrigation by long (300-400 m) deep (0.2-0.25 m) dead furrows.
It is the most efficient on nonsaline or low-saline irrigated lands levelled to inclined plane with homogeneous slope in the direction of watering (0,001 ≤ lf ≤ 0,007) under medium water permeability of soil. Proper application of discrete irrigation technique will allow saving 15-20% of irrigation water (in comparison with traditional irrigation) and raising crop yield by 10-15% due to uniform moistening of the irrigated plot.
Discrete irrigation technology can be implemented without special preparatory works on irrigation land plots of correct configuration provided with water level control in headrace network (free pressure of 0.6-0.8 m). In an old-arable zone, mass implementation of this technology will require some reconstruction of the irrigation network and fields.
Source: Recommendations for zoning of discrete surface irrigation technology (case study of the Uzbek SSR). SANIIRI Scientific Production Association, Tashkent, 1990. Developed by M.G. Khorst, L.A. Baykov, V.V. Dashina, Sh.A. Ishankhodjaeva under the academic editorship of Doctor of Technical Sciences N.T. Laktaev [in Russian]
For irrigated lands, the most promising irrigation method is the technology of surface irrigation by dispersed irrigation flow with discrete (intermittent) water supply to furrows. The main advantage of this technology is high uniformity of soil moistening along the furrow length, considerable reduction or even total exclusion of unproductive surface discharge.
The advantages of this technology are fully implemented on the irrigated plots levelled to inclined plane with equal slope along the furrow length at using watering units providing sufficiently high uniformity of distribution of irrigating streams over the irrigation front and special technical equipment that provides programmed changeover of the rate of water delivery to the units.
Flexible and rigid pipelines fully meet the requirements of the discrete irrigation mechanization technology. Discrete water supply provides alternating water inflow to two irrigating pipelines of equal length installed along the land plot. A regulating device is installed between them; at that, the slope gradient along the laying route is to be about zero.
There is also a method of furrow irrigation that includes discrete irrigation of the group of plots at a variable discharge of the irrigating stream supplied to furrows. The drawbacks of this irrigation method are soil erosion from water application, water losses due to deep filtration, nonuniformity of soil moistening along the furrow length, water escape from furrows at the end of the irrigated plot, short furrows.
Concentrated discrete irrigation by furrows at a variable discharge of irrigating stream allows reducing soil erosion, water losses due to deep filtration, water escape at the furrow end at furrow irrigation, raising uniformity of soil moistening along the furrow length, and extension of the length of irrigation furrows.
To carry out concentrated discrete irrigation at a variable discharge of irrigating streams supplied to furrows, the length of the irrigation furrows in the the irrigation system’s upper section is set less than that in the middle section, and the length of the irrigation furrows in the lower section should be more than that in the middle section. The bed of the upper section of the irrigation furrows is covered with meliorative polyethylene film with punched holes (perforations); at that, the distances between the irrigating holes become smaller with distance from the beginning of the furrows according as the discharge of irrigating streams lowers. The length of the furrows’ upper part covered by film is taken such as the discharge of the irrigating streams may not be higher than non-erodive discharge after the streams run over the upper section of the furrows.
Irrigation of land plots is carried out by the border strips consisting of group of irrigation furrows. Water application starts from the upper section at a fixed discharge of irrigating streams. After irrigating flows have traveled to the end of the land plot, water supply to irrigation furrows at the head of the upper section is ceased and the water from main pipeline at a fixed discharge is supplied to the beginning of the furrows of the middle section. The total discharge supplied to the irrigation furrows equals to the sum of the fixed discharge and water escape from the furrows of the upper section, due to which water is supplied to the furrows at a variable discharge of irrigating streams.
In the same way, irrigation pulse is supplied to the lower section. After irrigation pulse has been supplied to the lowest section, the cycle of irrigation of the border strip plots is over. Further watering of the border strips goes on by the same alternate cyclic water supply to the plots of the border strip until water application depth is reached.
Irrigation system includes an irrigation source, water intake structure, pressure main pipeline, gates with hydraulic drives installed at the inlet of transmission pipelines that have water outlets with hydrants to auxiliary/field/head ditches. The bed of the irrigation furrows is laid in their upper section with black meliorative polyethylene film with punched holes.
Control system consists of a central control panel (CCP) which includes a power supply unit, controller, switchboards, electrical hydraulic relay of KEG-I type [in Russian] ÊÝÃ-È). The CCP input is connected to a pressure main pipeline and the outputs are connected through connecting pipes to the inputs of taps the outputs of which are connected to the hydraulic drives of the transmission pipelines’ gates.
When constructing an irrigation system, the length of the furrows in the upper section is set less than that in the middle section and the furrow length in the lower section is more than that in the middle section.
The method of concentrated discrete water application by furrows at a variable discharge of irrigating stream is implemented as follows.
Before starting water application, the tap and hydrants open in all the transmission pipelines located on one irrigation strip. Duration of the plot irrigation pulse is set to the CCP controller. After this, the CCP starts to work and supplies water pressure to the hydraulic drive of a respective gate by turns with specified irrigation pulse time.
During water application, the gate at the upper section opens, the water from the main pipeline comes to the transmission pipelines and then through the hydrant in the upper section and auxiliary/field/head ditch comes to irrigation furrows. In the upper section of the irrigation furrows, the fixed discharge of irrigating streams is higher than non-eroding discharge. A part of the water in the furrows is absorbed by soil through punched holes in the film; whereupon, the discharge of irrigating streams decreases to the value of non-eroding discharge and then the water flows to lower sections of the furrows. The length of the furrows covered with film with perforation is taken so that the discharge of irrigating streams may become non-eroding after their travel over this furrows’ section. To improve the uniformity of soil moistening along the furrow length, the space between the punched holes is shortened so that to comply with the required decrease of the discharge of irrigating streams. After the irrigating streams run until the furrow end, the CCP switches off the gate in the upper section and supplies water pressure to the hydraulic drive of the gate of transmission pipeline in the middle section. The gate opens and watering of the border strip’s middle section starts. Water escapes from the upper section of the border strip come to the auxiliary/field/head ditch of the middle section. The water discharge supplied to the furrows in the middle section equals the sum of the discharge supplied from the transmission pipeline and the water escape from the upper section. The irrigating stream at the head has variable discharge. This provides faster travel of the irrigating stream over the upper section of the furrow and watering of the furrow’s lower section at a non-eroding discharge. During watering of the lowest section of the border strip, all water escapes are absorbed on the irrigated plot, because the length of the furrows in the lower section is more than the length of the furrows in the middle section. Watering of the border strip continues by the similar alternating cyclical water supply to all the border strip’s sections until water application depth is reached.
This method of water application allows preventing soil erosion, losses of irrigation water from irrigation land plots, reducing unproductive losses due to deep filtration, improving the uniformity of soil moistening along the furrow length, raising the efficiency of water application, and lengthening the furrows.
Source: State Fund of Intellectual Property of the Kyrgyz Republic
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