Question of the Week
Answer: Thank you for contacting ATTRA, the National Sustainable Agriculture Information Service for comparisons across drip, trickle, flood irrigation systems in terms of energy requirements.
Comparing different systems for energy requirements can be difficult. Below are just a few preliminary observations and things to consider:
1. Generalized comparisons across irrigation systems are tricky and somewhat unreliable. For example, there are some extremely efficient flood, ditch/furrow, and sprinkler systems, and some extremely inefficient drip systems.
2. I would treat published averages and energy savings with caution. Estimating energy-savings in the world of irrigation is a surprisingly difficult thing to do. After making various seemingly arbitrary decisions in how you calculate your baseline, you then need to cope with many inevitable unknowns: possible changes in the crop or variety being grown, acreage, management practices, weather-related impacts, equipment breakdowns, power outages, etc. Utilities, state agencies, and private companies in the energy conservation business often have an incentive to exaggerate energy savings.
3. People who study energy usage in irrigation are mostly engineers and so (not surprisingly) they tend to focus narrowly on engineering calculations: the volume of water you are moving, how far you are vertically lifting the water, how much pressure you are placing it under, and how much energy is "lost" to factors such as pipe wall friction, leaks, and various kinds of inefficiencies in pumps, motors, engines, nozzles, and so on.
These factors are all important, but equally important is how the system is managed. The connection between higher "pumping plant efficiency" and lower energy usage is usually taken for granted but is actually questionable. On this topic, I would recommend Blaine Hanson's article "Improving pumping plant efficiency does not always save energy."
Soil quality is another example of an important factor that is routinely ignored. There's a direct connection between soil quality and water-holding capacity, which reduces energy requirements. For example, one UC Davis study showed 50 percent higher water infiltration in organic plots compared to conventionally managed ones. Here's a link: http://www.sarep.ucdavis.edu/Grants/Reports/Temple/temple88-225.htm
4. Each type of system is also prone to environmental tradeoffs that go beyond energy. For example, flood irrigation often uses little or no energy, but can waste a lot of water and cause soil erosion. Drip systems often uses less energy than higher-pressure systems, but require intensive management and often heavy doses of biocides (such as chlorine) and acids to keep the lines from clogging.
For more information on irrigation and energy use see ATTRA's Irrigation Efficiency page.
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