June 30, 2006
Using Available Irrigation Water Strategically
One of the keys for getting through yet another year of drought is maintaining good water-management strategies.
Where ground water is the sole source of irrigation water, center pivots are the primary irrigation system. In this situation, the drought's biggest impact is the need to pump more water to make up for the lack of rain. By early summer, most of the water shortage has resulted from little or no spring rain. This means irrigation systems must be turned on earlier than normal, increasing the amount of water pumped and, along with it, the energy bill. However, as long as well capacity is adequate, the system should be able to keep up with crop demand since the greatest water demand period occurs in late July and August.
If ground water supply is limited or pumping is restricted, then the question is when to use the available water. Keep in mind that generally any water stress will reduce yields.
If we choose to allow some water stress during the early summer, we need to also understand that a center pivot's capacity to apply water may be less than what the crop needs later in the season - and without water stored in the soil profile, stress will quickly occur.
In other words, don't get too far behind - catching up is very difficult to do.
For irrigators who rely on surface water in the North Platte Valley, water has just recently been made available, but restrictions are in place. If you know you will have less water than your crops will need, you may need to forego irrigation of some fields.
Keep in mind that any water that leaves your field is lost for your use. An alternative to not irrigating a field is to irrigate more fields, but don't allow any water to leave your fields. This means timing set changes to coincide with when the water reaches then end of the field. This will result in water stress at the bottom of the field, but will allow you to use all of your water for producing a crop. Certainly return flow is important, but as an individual producer, you must make the best decision for your operation.
For surface irrigators one of the major challenges is uniform application. The practice described above results in poor uniformity by applying more water at the top of the field compared to the bottom. Yet when water is limited, we often are hesitant about using a practice or technology that is unfamiliar.
Surge irrigation is a tested and proven practice that has been available to furrow irrigators for a number of years. Surge can provide an even distribution of water on a field, reducing deep percolation and the amount of runoff.
In cooperation with the Bureau of Reclamation, the University of Nebraska has a limited number of surge valves available for loan during the 2006 growing season. Surge is a practice that should be used, especially when water is limited.
C. Dean Yonts
Panhandle Research and Extension Center, Scottsbluff