IRRIGATION SCHEDULING
Learn how efficiency and distribution uniformity impact your crops.
From an on-farm water management standpoint, it is desirable to achieve four things during an irrigation event. A professional wants to apply the correct depth of water at the correct time, giving the same amount of water to every plant in the field and avoid unrecoverable losses such as excessive evaporation.
The Cal Poly San Luis Obispo Irrigation Training and Research Center has developed the software, classes and procedures for on-farm irrigation evaluations (for drip, pivot, undertree sprinkler, linear move, wheel line and hand move, solid set, furrow, border strip, and basin systems) that have been used for more than 40 years in California. Each year we have a one-week short course for evaluation teams and others that combines lectures, laboratory and field exercises. The emphasis of the annual short course is on drip/micro irrigation simply because in California that is where the interest lies.
I want to strongly emphasize the need for standardization of formulas and terminology. Without standardization of what to measure, how to measure things, how to combine data into formulas and the formulas themselves, everyone just talks past each other. There is still a problem in our irrigation industry with people wanting to reinvent the wheel. There is no one perfect term/formula that describes all the aspects of irrigation performance. However, the 1997 landmark publication on the topic “Irrigation Performance Measures: Efficiency and Uniformity” (found at
itrc.org/papers/ efficiency.htm) is as valid today as it was more than 25 years ago.
Top formulas
The two most common terms and their formulas are irrigation efficiency, expressed as a percentage value between 0 and 100, and distribution uniformity, expressed as a value between 0.0 and 1.0. They are both defined in the Irrigation Association’s study materials for certified irrigation designers in drip/micro, as well as the CAIS certification.
The formula for irrigation efficiency is: IE (%) =
Irrigation water beneficially used Irrigation water applied
× 100
Irrigation efficiency recognizes that some of the applied water is not beneficially used; we can get close to 100% but it is impractical in the field. Typical uses that are considered nonbeneficial are excessive deep percolation beyond what is needed for salt leaching, uncollected field runoff and excessive evaporation. For example, a center pivot that rotates rapidly in a hot, dry environment may lose most of its applied water to nonbeneficial evaporation from plant and soil surfaces. Hence, the recommendation with pivots is to rotate as slowly as possible without having runoff. Interestingly, one way to achieve a high irrigation efficiency is to underirrigate. With underirrigation there is typically little to no deep percolation or tailwater runoff from a field. But in that case, having a high irrigation efficiency does not lead to maximum crop production/quality per acre. This points out the inadequacy of any single term to describe irrigation performance.
INTERESTINGLY, ONE WAY TO ACHIEVE A HIGH IRRIGATION EFFICIENCY IS TO UNDERIRRIGATE.
Summer 2023 | Irrigation TODAY 17
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40
