Farm & Ranch
Have you ever wondered how much the efficiency of your irrigation methods impacts your pumping costs? Have you ever wondered how much it costs to water your irrigated crops? What is the true value of rainfall?
Below are a couple of charts showing just how much irrigation efficiency can matter to you. The first chart, "Irrigation Application Efficiencies Really Matter" is from the High Plains Underground Water Conservation District No. 1. This chart shows how much water you have to pump to provide varying amounts of water to a crop at varying pump efficiencies. If you intend to apply a specific amount of water to your soil, knowledge of your system’s current efficiency must be factored in to determine how much will actually reach your soil.
| Irrigation Application Efficiencies Really Matter | ||||
|---|---|---|---|---|
| Application Efficiency | Water required for 12" of water to the crop | Water required for 18" of water to the crop | Water required for 20" of water to the crop | Water required for 24" of water to the crop |
| 50% | 24" | 36" | 40" | 48" |
| 60% | 20" | 30" | 33.33" | 40" |
| 70% | 17.15" | 25.7" | 28.7" | 34.3" |
| 80% | 15" | 22.5" | 25" | 30" |
| 90% | 13.33" | 20" | 22.2" | 26.67" |
The chart "What is Rainfall Worth" [pdf, 11 kB] estimates what it might cost in 2006 to apply that water, also at various pump efficiencies. Other factors such as wind also have a bearing on how much of the water you pump reaches the soil. Typically, you can figure that for every 10 mph of wind, there is a corresponding 10 percent drop in water application efficiency.
For example, a center pivot with drop lines three to four feet above the soil is normally about 80 percent efficient. Factor in a 30 mph wind and the water application efficiency drops to 50 percent. It is impossible for many farmers with limited water availabilities to overcome such a high percentage water loss. For all irrigators, it would be best to avoid irrigation in such conditions, not only because of the wasted ground water, but also because of what you paid to pump that water from the aquifer to the surface.
Another factor that determines how much of your pumped water actually reaches the soil is the percentage of actual soil surface that is wetted. Higher summer temperatures and lower humidities add to evaporation losses as compared to normally cooler temperatures and higher humidities during pre-plant moisture application.
Tillage practices such as furrow dikes can improve water infiltration rates and reduce runoff. Studies have shown that yield increases of 30 pounds of cotton lint or 350 pounds of grain sorghum per acre are possible for every additional inch of water collected and stored in the soil through the use of furrow dikes.
When you sell your crop, you are also selling the water you pumped along with it. What is your water worth to you? This information condensed from an article written by Scott Orr and published in The Cross Section, the monthly newsletter of the High Plains Underground Water Conservation District No. 1. Their web site covers a variety of topics related to water and water conservation.