It may be somewhat trickier to pull off, but germinating lettuce with drip irrigation offers certain advantages over sprinklers.
Central Coast water quality issues could be an impetus for lettuce growers to switch to drip, according to Michael Cahn, University of California Cooperative Extension (UCCE) irrigation and water resources farm advisor for Monterey, San Benito, and Santa Cruz counties.
“There are potential impairments to our water supply including factors such as bacterial pathogens, nutrient leaching, off-site movement of pesticides and sediments, and excess salt,” he said at a UCCE-sponsored irrigation and nutrient seminar at Salinas.
“There are several potential limitations to drip germination. They include factors such as lateral movement of water, total water use, nitrate leaching, and weed control.”
To get effective germination, there must be sufficient lateral movement of moisture from the drip tape, and both chemical and physical factors affect that movement.
Several research and commercial trials were conducted in 2005 and 2006 at various locations in the Salinas Valley to identify the best strategies for accomplishing lateral moisture movement, as well as to compare water use and nutrient leaching between drip and sprinkler germinated systems.
“Numerous factors affect the lateral movement of moisture from the drip tape,” Cahn notes. “It can be affected by the discharge rate of the tape, emitter spacing on the tape, and the depth of the drip tape. It can also be affected by bed compaction and mulching.”
Various discharge rates were used, including .22 gallons per minute (gpm), .45 gpm, and .67 gpm. Measurements were taken for lateral movement of moisture, vertical movement, water use, germination rate, mineral loss, and others. Yield and quality data were also recorded.
“Drip uses less water when it works right, but as much or more than sprinklers when it doesn't,” Cahn says. “We need to match drip to the right soils. In the commercial trials, water use was similar for drip and sprinkler, nitrate losses were similar, and germination rates were similar.”
For growers who want to use drip germination, there are several best practices that can be generally followed to maximize results, according to Cahn. They include mulching beds, shallow placement of tape (2-3 inches from the surface), and using a medium flow tape with an 8-inch emitter spacing.
“One critical factor is that the drip system must have high application uniformity,” Cahn says.
“We also had better results when we compacted the beds with a weighted roller and planted slightly deeper than with sprinkler germination.”
Detailed results obtained from the trials can be accessed at UCCE's Monterey County Web site: www.cemonterey.ucdavis.edu.