Furrow irrigation
Furrow irrigation is the most complete method of free-flow (gravity) surface irrigation. According to its effect on soil and plant, formation of water, air, and nutrient regimes, it is applicable not only for vegetable growing, but also for field crop cultivation. Surface furrowing enables using irrigation practically for all types of soil, reliefs and slope grades with small scale of leveling works. Irrigation furrows are trenched simultaneously with sowing or intertillage of spaces between crop rows, notably furrowing is well linked with the crop sowing and nursing technology.
Tractor cultivators equipped with claws-furrowers are used for trenching irrigation furrows.
At furrow irrigation, soil conditions, the land relief and slope, row-spacing width or interval between the furrows are taken into account.
Depending on the texture and cultivation state of the soil and particularly on ploughing horizon (depth of tillage) and purpose of irrigation (stimulating, vegetative, off-season), furrows can differ by their cross-sections and consequently by volume of filling.
Depth and width of irrigation furrows. According to depth, volume of filling and consequently hydraulic features furrows are broken down into shallow, medium-depth, and deep ones. Shallow furrows are 10 15 cm deep, 30 35 cm wide on the top; medium-depth furrows are 15 20 cm deep and 40 45 cm wide on the top; and deep furrows are 20 30 cm deep and 50 60 cm wide on the top.
Shallow furrows are used for crops with narrow row-spacing and for band sowing. They pass through the plowing horizon (so called S horizon) and have good water yield.
Medium-depth furrows, which are trenched with a row-spacing of 60-70 cm, pass through the plowing horizon and have not only good water yield but also considerable volume of filling.
Deep furrows are made with a wide row-spacing (80 90 cm). Their depth is 20 25 cm and at off-season irrigation come up to 30 cm. Such furrows have a large volume of filling, but poor water yield.
Furrows-slots designed by Southern Research Institute of Hydraulic Engineering and Land Reclamation (YuzhNIIGiM) are applied with the view of enhancing furrow water yield. The furrows-slot has the overall depth of 30 40 cm; the slot is 2 3 cm wide and 15 20 cm deep. At furrow irrigation of grain and perennial grasses, medium-depth or deep furrows are made to avoid crust formation in these during the autumn-winter period. If deep furrows are trenched since early autumn simultaneously with sowing of winter cereals or perennial grasses, more precipitation and melt water are retarded therein, which contributes to better sprouting and establishment of plants. In addition, preliminary furrowing enables as appropriate carrying out stimulating irrigation. In areas subject to dust storms, sowing of grain and other crops along with trenching furrows will protect these crops from shifting by wind. For the purpose of protecting vegetable crops from shifting by wind (crop shearing-off by blowing sand), terrace furrows are used. As opposed to regular furrows, these furrows have small terraces, viz. benches on which cabbage or tomato seedlings are pricked out by using machines, and contour bunds protect the plants from shifting by wind. When seedlings have been pricked out, they are to be irrigated.
Interval between irrigation furrows. As it has been mentioned above, the scope of the usage of furrows is extremely wide; they are used not only for irrigation but also for water regulation. For example, deep furrows-slots can transfer surface flow to subsurface runoff. Subject to the purpose, furrows are cut with different intervals. For irrigation of intertilled crops, horticultural, berry and vegetable crops, furrows are cut in spaces between rows. With narrow row-spacing and band sowing shallow furrows are used; with row-spacing of 80 100 cm, deep and wide furrows are used. With long furrows (300 400 m), where water discharge comes to 3 5 l/s, row-spacing is made as much as 90 100 cm wide. Such a width of row-spacing is required not only for trenching deep and wide furrows, but also for inter-row cultivation of crops, because labour productivity rises with long furrows and higher speed of tractor aggregates. However, the interval between furrows is determined not only by row width. When irrigating seeded furrows or irrigating furrows with wide-row planting of grain and grasses, soil texture, degree of soil moistening, proximity of the stand of groundwater level, and other factors should be taken into account. On inundable lands with close stand of groundwater level, furrows are trenched not in every space between rows, but in every second one. Especially such furrowing and irrigation is efficient for crops of narrow (45 50 cm) row-spacing. In this case, furrow ridges are not washed away, and stay dry making it easier for an irrigator to pass through. Irrigation of every second row allows reducing water application rate from 700 800 to 300 400 m3/ha, i.e. lowering by 45 50%, and due to saving time for irrigation it allows raising labour productivity by at least 35 40%. In the early stage of plant growth and development, at carrying out of feeding irrigation when there is no need in supply of large quantity of water, irrigation of every second row-spacing is especially efficient.
According to soil conditions, land topography, slope, and irrigation technology applied, irrigation furrows can be broken down into two types: dead (spur) flooded and through furrows.
For irrigation of intertilled crops at fields with a slope grade of 0.1 0.2, furrows are cut not with maximum grade, but at an angle to contour lines (cross-contoured) or very close to them (contour furrows). In these cases, the length of the furrows and discharge in them are decreased by 25% as compared with traditionally adopted.
To reduce soil erosion in some farms of submountain areas, they preliminarily moisten the upper part (1/3 1/2) of the furrow length at minimal discharge; then it is increased, and after flow travel up to the furrow end it is again minimized.
Source: www.skyrage.ru
