Assessing irrigation options always interests growers A topic that's constantly on the minds of alfalfa growers is irrigation efficiency and ways to apply water more uniformly.

Hand-move, wheel-line, side-roll or other periodic-move sprinkler systems are commonly used in alfalfa. But, uniformity depends on hydraulic losses, catch-can uniformity and maintenance.

Center pivot and linear move-sprinkler machines are alternatives for greater uniformity, but recent technology has added a solid-set option. It's a flexible, PVC sprinkler pipe that can be lifted over the top of the cutter bar and its being put to use by a Minden, Nev., alfalfa grower, reports Lee Tecklenburg of Sacramento, territory manager for CertainTeed.

Called Serta-Set, the innovative solid set system has an especially good fit for uneven ground or odd shaped fields, points out Tecklenburg. It's being used in other crops, but to his knowledge the Nevada grower is one of the first to use the flexible sprinkler pipe in alfalfa. Unlike aluminum pipe that's sealed by water pressure, Serta-Set features a flexible joint that rotates or moves, thereby preventing leakage. The bottom line, he maintains, is more uniform application of water.

Growers looking for more efficiency may also want to investigate subsurface drip and center pivot or linear move sprinkler machines. The different options were topics of discussion at the National Alfalfa Symposium in Las Vegas.

Advantages cited for buried drip include precise water application throughout a field, higher yields, reduced water use and lower fertilizer and cultural costs. On the other hand, "a rough estimate" for amortized capital cost is $150 to $200 per acre.

In an Imperial Valley study, drip tubing was initially placed 16 to 18 inches deep with emitters at a 40-inch spacing and a nominal discharge rate of 0.5 gallon per hour. Drip tubing was eventually placed 25 to 28 inches deep to avoid wetting of the soil surface and interference with harvest.

Compared to furrow irrigation, water use was six percent to 10 percent lower and yields were 22 percent higher when drip tubing was at a 16- to 18-inch depth. At 25 to 28 inches, water use was about the same as furrow irrigation, but yields were 12-17 percent higher.

Drip has a "potential" distribution uniformity of 80-90 percent. Center-pivot and linear-move sprinklers have the same rating due to the more or less continuous movement reducing the effect of wind on uniformity. Potential uniformity for border or flood irrigation is 70 to 85 percent.

The question of return on investment for converting to continuous move or drip systems isn't clear-cut. Reasons cited were little information on conversions and the effect of site-specific conditions. But as a general rule, "the more marginal the site-specific conditions, the more likely that converting to continuous move sprinklers or drip irrigation will increase profit." The conditions include water quality and soil quality - texture, variability within a field and hardpans or clay lenses.