Surface Irrigation Tips for Limited Water

Adjustments for surface irrigation are crucial to operate with less water.

Advances in irrigation technology have resulted in improved sprinkler and drip irrigation systems, but surface irrigation still accounts for about half of the irrigated acreage in Colorado. While these systems are still used for a variety of good reasons and meet the needs of many growers, surface irrigation is inherently inefficient (25 to 60% application efficiency) and non-uniform. When water is plentiful, low efficiency is usually overlooked and becomes more of a water quality problem (leaching and runoff) than a water quantity problem. However, in water short years, inefficiency and poor uniformity results in water lost to crop productivity and all management practices (Table 1) to improve efficiency should be considered.

Figure 1. Long runs combined with coarse-textured soils and/or low stream size require extra water to adequately wet the bottom of fields.

The main cause of inefficiency in surface irrigation results from the extra irrigation water that is necessary to get water to the end of the row. This problem becomes more acute on long runs (>1,000 ft.) and/or coarse-textured soils. As Figure 1 shows, this leads to poor uniformity with excess water applied at the upper end of the field and not enough on the lower end. Additionally, the extra set time required to adequately soak the bottom of the field results in runoff losses. This poor uniformity can be improved by a variety of management practices:

  • Shorten row length
  • Increase stream size and cutback
  • Use optimum set time
  • Pack furrows
  • Use surge valves or manually surge rows
One adjustment that should be considered under tight water supplies is shorter runs. This is especially relevant in situations where growers are planning to reduce their irrigated acres. In these situations, a potential strategy would be to leave fallow or plant a dryland crop on the lower one-third of long runs, especially on fields that have a sandy loam texture or sandier. This strategy allows growers to use shorter set times and would keep water from being wasted trying to push to the field bottom, particularly on the first irrigation.

Increasing stream size helps increase advance rate, but has its limits with erosion and blowing out furrows. Additionally, increasing stream size without cutback will result in more runoff if growers allow for a full wetting of the furrow. Polyacrylamide (PAM) can help maintain furrows when using high flows, but will not help water advance. In fact, PAM usually increases infiltration on many soils, and may increase advance time if flows rates are not increased by two-fold. However, when lateral wetting to the bed center is desired, for example when the crop has to be irrigated up, PAM has been shown to improve lateral infiltration. In these situations PAM may save water because set times might be shorter to accomplish lateral soak. PAM is also appropriate for fields where inefficiency is caused by poor infiltration due to short and/or highly sloped fields with fine-textured soils. On these fields 10 ppm of PAM in the irrigation water may help soak up the field without having to run the water for extended periods of time.

Furrow firming (packing) is also a practice that can increase advance rate in many situations. In a study at Scottsbluff, Nebraska, (Yonts, 2000) advance time was reduced by 18 percent for either surge irrigation in a soft furrow or continuous irrigation in a firmed furrow when compared to continuous irrigation in a soft furrow. When the two treatments were combined, advance time was reduced by 27 percent compared to continuous irrigation in a soft furrow. These results indicate either furrow firming or surge irrigation equally reduces furrow advance time, but a greater reduction can be achieved when the two methods are used together. However, furrow firming will be of limited value if soil moisture contents are extremely low.

Most surface irrigation systems are inherently inefficient and limit irrigation options during dry years. However, growers can make some management adjustments to improve their systems and maximize water available for crop production.

Table 1. Potential adjustments for surface irrigation systems.
* See Guidelines for Using Conservation Tillage Under Furrow Irrigation TR02-6 at http://www.colostate.edu/Depts.AES/

By Troy Bauder
Extension Water Quality Specialist
Dept. of Soil and Crop Sciences
Colorado State University

References: C. Dean Yonts. 2000. Firming Irrigation Furrows to Improve Irrigation Performance. Neb. Guide G1340

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