The border irrigation concept is to flush a large volume of water over a relatively flat field surface in a short period of time. The borders are raised beds constructed in the direction of the field's slope. Water is released at the field's high end and the borders guide the water down the slope as a shallow sheet that spreads out uniformly.
Border irrigation is best-suited for flat planted or drilled crops on precision-graded fields with slope in only one direction. All field operations, including planting, should be with the slope. Planting across the slope tends to restrict the water flow, especially on fields with less than 0.1 foot fall per 100 feet.
Drain furrows can limit the effectiveness of border irrigation if they cause the water to spread unevenly between the borders. Fields with slopes in two directions are not as well-suited to border irrigation, but it may be possible with a narrow border spacing.
Border spacing is affected by soil type, field slope, pumping capacity, field length and field width.
A cracking soil is sometimes difficult to irrigate, but with borders the cracking actually helps. The tendency on fields with side slope is for the water to flow to the lower side and not spread out uniformly between the borders. Soil cracks lessen this effect because the water spreads laterally as it follows the cracking pattern.
The border spacing on clay soil is generally between 200 and 300 feet with the narrower spacing on fields with side slope.
The border spacing on sandy and silt loam soils that tend to seal or crust over is more of a challenge. On these soils, the border spacing ranges between 100 and 200 feet with the narrower spacing on fields with side slope.
Experience has shown that crop stubble on sandy and silt loam fields can help the water spread out evenly between the borders
The pumping capacity and field dimensions (length and width) determine the number of borders needed and how many can be irrigated in a reasonable time.
Calculations can help to estimate the time required to irrigate a border. It is usually possible to work toward approximately 12-hour set times that fit well with water and labor management. Regardless of how long you have been pumping, the set should be changed once the water reaches 75 percent of the distance.
Borders can be constructed with different types of equipment. The method used is affected by whether or not the border is going to be planted. A settled border height of 2 to 4 inches is adequate on fields with no side slope, but a 4- to 6-inch settled height is required on fields with side slope or potholes.
If the border is constructed with a disk-type implement, an effort must be made to fill or block the ditch left at the base of the border so it will not act as a drain furrow. Borders should stop at least 50 feet from the low end of the field so drainage is not restricted.
Water is delivered into the borders from a canal, pipe or irrigation tubing. If irrigation tubing is used, it should be the heavier 9- to 10-mil tubing. The 2.5-inch adjustable plastic gates deliver 65 to 75 gpm each and can be installed in the tubing.
If border irrigation can be used on a field that is usually flood-irrigated, it can provide certain advantages:
- Less production area lost with border than with levees.
- Improved ability to irrigate small crop.
- No need to repair or rebuild border between irrigations.
- Borders do not restrict field drainage as levees do.
- Better possibility of growing the crop on the border.
- Easier to share water with rice.
Border irrigation will not work on all fields and is not necessarily a better method than planting on good beds and furrow irrigating. However, if a grower wants to move toward flat planting and reduced tillage, border irrigation may be more appealing than flood. More information on border irrigation is available through local county Extension offices.
This is one of several articles on drainage and irrigation water management. If you have questions or suggestions on topics please contact me: Phil Tacker, 501-671-2267 (office), 501-671-2303 (fax), 501-944-0708 (cell), or [email protected] (e-mail).
Phil Tacker is an Arkansas Extension ag engineer.