Border ditch irrigation

Border ditch irrigation is applied for water application to narrow-row crops, notably grain cereal, annual and perennial grasses. However, it can be used also for water application to other crops in combination with ridge tillage. At border ditch irrigation, water flows over the surface covering it by water sheet of 2…3 cm. To control the direction of the water current, the border ditch (strip) is narrowed by small irrigation borders or open ditches. They distinguish two types of border ditch irrigation: flooding from horizontal ditches (with lateral water outlet) and flooding with head water inlet to an irrigation ditch.

Features of border ditch irrigation: higher productivity in comparison with furrow irrigation, a little more uniform (comparatively) moistening, since the entire field surface is moistened, but water losses takes place on the entire surface, the aeration (ventilation) becomes broken, the activity of useful microorganisms becomes worse. Border ditch irrigation has the same drawbacks as the furrow irrigation.

Flooding from horizontal ditches is usually used in submountain regions for irrigation of crops, grasses, horticultural (orchard) crops, and grapes, where slope gradients come to 0.02…0.03 and more. Horizontal ditches are cut by using ditchers of KZU-0.3 or KOR-500 types to a depth of 0.35…0.4 m almost along the contour lines of the site at a slope gradient of 0.0005...0.001 at 20..30 m interval and not more than 50 m apart from each other. To irrigate orchard crops and grape, horizontal ditches are cut along rows from the bottom part in such a manner that the ditches can be used not only for irrigation but also for capture and usage of spring meltwater and storm water.

Flooding from horizontal ditches is applied on heavy loam soils and unleveled or poorly leveled lands, as soils in submountain areas are rarely developed well enough and often pebbles underlie them at a shallow depth. Therefore, horizontal ditches on uneven microrelief have usually great turns. In case of large unevenness of the relief, ditches are cut being oriented by command points, notably by hillock gullies. In this case, irrigation is carried out by free flooding. The length of the irrigation border ditches from horizontal ditches varies from 100 to 300 m and over depending on the microrelief.

The entire field between temporal irrigation ditches is divided into border ditches (strips) by irrigation borders (bunds). The border ditches are cut along the slope; the longitudinal gradient ranges from 0.02 to 0.0005, better is 0.01…0.001. No transverse slope is allowed. The border ditch length is 50…300 m, more often is 100…150 m. The border ditch width is 10…12 m on the plain surface and 4…8 on the rough surface. In addition, the border ditch width should be divisible by the width of a seeding-machine claw. The bund height should be 15…20 cm. Water current is supplied to the border ditch at a rate of 3…6 l/s. The water flows breaking down into 5…8 cm water sheets and is gradually absorbed. If the supplied water quantity slightly exceeds its absorption rate, the water supply rate is reduced or water supply is stopped when the water runs up to 2/3…3L of the border length. Consequently, water application is executed by using power water. Irrigator’s labour productivity per shift is 2 ha on the average.

Border ditch irrigation from horizontal ditches is performed at higher discharges, i.e. from 25 to 100 l/s. Because of great slope gradients and higher discharges, water is applied to the matted soil, that is to perennial grasses or crops of cross sowing. This will protect the soil from scouring.

When irrigating from horizontal ditches, water is supplied to the ditch end and is let out to the surface through a water outlet or cutoffs at the highest points. The interval between the water outlets or cutoffs is chosen so that the fans of water flow from different discharges merge and there is no dewatered soil at interfaces. Only very experienced irrigators possess high skill of such water application. To avoid water escape, water comes from an upper border ditch to a downstream canal and is used for irrigation purposes. For this purpose, the downstream horizontal ditch is made single-sided. The water that came from the upstream accumulates in this ditch, where water is added in proportion to about 2/3 of the discharge water, and it is also involved in the water application process. The discharge water from the second canal runs to the downstream third canal, where again new water is added to it, and that is also used in the water application process. If a water application process is organized properly, at which all the horizontal ditches along the slope are engaged and water from an upper irrigation ditch flows to lower ones, watering from the horizontal ditches takes the form of cascade irrigation. Specific water discharge per 1 m of the width of a border ditch is determined experimentally. Because this type of irrigation is carried out on matted soil or dense stand, the specific discharge ranges from 10 to 15 l/s. At low water discharge, it is impossible to uniformly distribute water over an area adjacent to the water outlet, and water application becomes inefficient.

Flooding with head water inlet is used for irrigation of close-sowing crops, but it is suitable as well for irrigation of fruit crops, small-fruit crops, and other crops. It is used on low and high gradient slopes, that is to say as to slopes it has wider range than flooding from horizontal canals. Longitudinal slopes of 0.002…0.01 are the most acceptable. Water from field drain irrigation ditches or field pipelines and with longitudinal scheme from field (auxiliary) ditches comes to border ditches with a width of one (3.6…4.2 m) or two (7.2…8.4 m) passageways of a disk drill; these irrigation ditches are bounded on sides by earth bunds 0.3…0.4 m high. The bunds are arranged simultaneously with the passage of a seed drill. When sowing grain crops and grasses, these bunds are seeded. A ridger-type ditching machine is installed before the seeding machine for making bunds. Its grasp width (coverage) is equal to the sowing machine’s grasp width (3.6…4.2 m). When moving, the ditching machine cuts 2…3 cm thick loose soil, passes it through a narrow hole (0.4…0.5 m) and dumps a bund. Lest the bund should break down during a passage of a seeding machine, the rods of a seed distributors passing over the barrier are properly adjusted.

Bund ridging when making border ditches without unitizing with a seeding machine is carried out by using ditchers-bund makers. In this case, bunds are made at an interval of 3.6…4.2 m (sowing width); in the case of absence of longitudinal slope, the border ditch width may come up to 20…25 m. The productivity of bund shaping can reach 1.5…3.4 km/h. If there are no special machines, flooding strips for water-charging irrigation can be cut by using ploughs with elongated second and third mouldboards.

At flooding irrigation with head water inlet, a special focus is made on smoothing the border ditch surface and presence of transverse slope grade. Transverse slope is not desirable at all. A permissible transverse slope grade even for narrow (3.6…4.2 m) border ditches should not exceed 0.002…0.003. If transverse slopes are greater and border ditches are even wider, water runs to a lower bund and non-uniformly moistens the bund surface. Water frequently breaks through the bund, and at watering it flows not along but across the border ditch, destroying other border ditches. A special attention is to be paid to smoothing of pre-bund furrows formed when shaping bunds. If there are pre-bund furrows, water does not inundate border ditches, but goes along the bund and destroys it at backwater points. For this reason, light sweeps should be attached behind the seeding machine when making bunds simultaneously with sowing. When making wide (15…20 m) border ditches after shaping bunds by using a ditching machine-leveler KZU-0.3B (in Russian: ĘÇÓ-0,3Á), light tractor sweeps run before sowing to smooth pre-bund furrows. In addition to smoothing the surface, a watering board is used prior to sowing crops for ensuring uniform water distribution over the border ditch at water application.

Flooding irrigation with head water inlet has the proper geometry of the arrangement of border ditches and irrigation network elements on the irrigated plot; this is why it is known as cultivation flooding. With this method, the water application rate varies from 1000 to 1500 m3/ha. As a rule, border ditch irrigation is carried out at a water travel rate. In this case, such water discharge q is chosen per border ditch so that the water quantity supplied for water application time t should correspond to the targeted water application rate, i.e. the quantity of the water supplied should be equal to the quantity of the water absorbed. Knowing the specific water discharge q per 1 m of the border ditch width and the border ditch width a, the water discharge per a border ditch can be calculated.

With irrigation at a water travel rate, water supply to the border ditch is stopped after water has passed 75…85% of the border ditch length in order to avoid tail escape; this requires irrigators’ high skill. Watering at a water travel rate enables lowering the water application rate down to 600…800 m3/ha. The possibility to adjust water application rates by skilful selection of q, t and l makes flooding rather a flexible way of gravity irrigation. With the same specific water discharge per border ditch, the slope grade reduction by 2 times usually leads to the extension of the irrigation time and increase in the water application rate by 60%, while the labour productivity declines twice as much.

In addition to irrigation at a water travel rate, border ditch irrigation can be performed also by alternating stream. Alternating-stream irrigation, i.e. the combination of water travel rate and recharge rate allows more exactly adjusting the water application rate, especially if it has to be increased for water-charging irrigation. At alternating-stream irrigation, the flooding strip is watered, just like a flood-free furrow, in two steps: moistening and recharge. For border ditch moistening, water is provided at a great discharge – from 10 to 15 l/s and over per 1m of the border ditch width, then it is lowered by 2…3 times and recharging is carried out. With long (300…350 m) border ditches, specific discharge during a recharging period is recommended to be not less than 3…4 l/s, otherwise it will not only drag out the water application process but also will not provide uniform coverage of the surface with water sheet. The border ditch irrigation with head water inlet with water evacuation is generally not admissible, because it results in water erosion. On steep slopes, if water application can not be executed without partial discharge, as with through-furrow irrigation, discharge water should be used at the downstream plots. The length of flooding border ditch with head water inlet depends on mechanical properties and, particularly, on water permeability of soils as well as on slope grade. On light water-permeable soils, they are about 1.5…2.0 times shorter than on heavy soils and usually do not exceed 100…200 m. If the field surface is properly leveled, the ditch length may come up to 400…600 m. Elongation of a flooding ditch requires significant increase of water discharge to ditches.

Border ditch irrigation, just like furrow irrigation, requires control of moistening uniformity. Properly established control of soil moistening uniformity, and consequently of watering quality is a direct duty of agronomist–field crop grower, because he is eventually responsible for irrigation water-use efficiency. As well as with furrow irrigation they keep a watch on the depth and pattern of soil wetting along the ditch (strip) length at its beginning, middle, and end sections. To this effect, soil samples are taken by using a bore to define its humidity and uniformity coefficient Uc which at efficient water application is supposed to be equal to 0.85…0.9.

The possibility of cutting flooding ditches varying in width and length, supply at concentrated and higher water discharges, presence of sowed irrigation borders (bunds), possibility to maneuver water application rates from 600 to 1500 m3/ha and more and, finally, high labour productivity at watering from 5 to 15 ha and more per shift make this irrigation method particularly promising for grain-producing steppe regions.