With irrigation likely the most costly input for over half of West Texas cotton production, having a system properly primed for 2008 should be at the top of a grower’s to-do list.
And knowing the amount of preplant irrigation needed can help growers get the best jump on a healthy stand next spring, says Dr. Dana Porter, Texas A&M University agricultural engineer who specializes in irrigation at A&M’s Lubbock Research and Extension Center.
Porter was among those just short of spellbound over the amount of rainfall the Texas High Plains received in late spring and early summer. Soil profiles were overflowing for many. And cool weather made much cotton 2-3 weeks late. That meant center-pivot LESA (low elevation spray application), LEPA (low energy precision application) and other irrigation circles weren’t used nearly as much in the spring. Nor were subsurface drip irrigation (SDI) systems, and furrow systems using both poly pipe and other types.
Even though cotton was being pressed to obtain enough heat units, growers weren’t complaining about the reduced natural gas, electric and diesel bills which resulted. Still, good managers were aware of the need to maintain an efficient system, because 2008 could mean the return of dry weather that is all too common for the region that averages barely 18 inches of rainfall per year.
A good maintenance program should involve checking older systems for efficiency and how they will be expected to function, says Porter, given the water availability and degree of yields expected.
“The first question to ask is if the system is performing according to its specifications,” she says. “Does it need to be repaired or upgraded, or does the center pivot or linear system need to be re-nozzled?”
Another question should be whether the nozzle package has “drifted” over time, or if broken or lost nozzles may have been temporarily replaced with the wrong size nozzle. “Such quick fixes repeated too often over time can lead to poor distribution uniformity,” says Porter, noting that growers should consider the last time they conducted a distribution uniformity test, calibrated the pivot, or just made sure the nozzles on the pivot match the design nozzle package printout.
For SDI systems, which now water more than 250,000 acres in Texas, make sure the filtration and maintenance program are adequate. Pressure gauges and flow meters should be used, and can help in troubleshooting system efficiency, as they can indicate problems such as leaks or plugging in the system, says Porter.
Match the System
New LESA, LEPA, SDI and furrow-irrigation systems are needed from time to time to replace worn-out systems, to replace less efficient systems with more efficient ones, or to add new irrigated acres. Porter encourages growers to select the right system and specifications for the task at hand.
Texas A&M research at the Halfway station, located north of Lubbock, indicates that in limited irrigation situations, SDI and LEPA systems can lead to higher yields. In situations where full irrigation is available, LESA systems can provide as good or better yields. For any system, good management is key to good performance and efficiency.
Selecting the right system for your situation should begin with a good system design. “That will likely require working with a certified irrigation designer or professional engineer,” says Porter. “Design the system for realistic well capacities. Consider whether the water delivery is likely to decrease during the season.”
Prepare for Pre-Watering
A preplant irrigation is often needed to generate the stand that will lead to a good crop. But growers can refrain from applying too much water by knowing their soil profile before they crank up engines, motors and pumps.
The recommended soil moisture storage is about 75% of full field capacity. “This will allow for room to store water from timely rains,” says Porter. “If the goal is to apply water to moisten the root zone to a target level, it’s essential to know how much water the soil will hold at field capacity, and how much water is already in the soil.”
Dr. Dana Porter
LEPA irrigation saves energy and conserves water.