Subsurface drip in alfalfa has its challenges. Yield does not appear one of them.
Seth Rossow manages Wilgenburg Dairy’s alfalfa operations near Chowchilla, Calif. Wilgenburg milks over 2,000 cows in nearby Hanford and uses alfalfa grown in Madera County to feed his dairy herd.
“I was hired here about seven years ago to change things and make them more efficient,” Rossow said. “I’ve done that.”
Rossow answered questions about his transition into buried drip during a field day sponsored by Netafim. The field day was intended to help growers hear first-hand reports of transitions into subsurface drip irrigation (SSDI) in alfalfa and the challenges involved.
Netafim held three such field days in the San Joaquin Valley, offering growers a chance to hear from other growers who have employed drip technology in the forage crop.
Wilgenburg Farms has 700 acres of alfalfa growing over SSDI near Chowchilla. Rossow says the advertised water savings spread over 6.5 cuttings per year isn’t as large an issue for him as some of the other benefits. Rossow saves about six inches of water per season with SSDI over flood.
Rossow uses about 4.5 acre feet of water to grow a crop that once took him five acre feet to grow. The main benefit is the yield bump he gets from SSDI.
“Now we’re getting 12 tons per acre where we were getting 8.3 tons,” Rossow says.
He likes to talk in water use efficiency and distribution uniformity across the field as a big benefit of SSDI rather than pure volume savings. He believes the more efficient the flood system the less a grower will likely realize a significant water savings.
Benefits of SSDI
Distribution uniformity is one of several benefits of subsurface drip in alfalfa that University of California alfalfa specialist Dan Putnam likewise touts when looking at the irrigation system.
“We know with surface irrigation systems, like flood, you start at one end of the field and the water moves across, leaving water to sit on some portions of the field longer than others,” Putnam said.
This has built-in problems, according to Putnam. Water infiltrates more on some sections of the field compared with others, making it non-uniform.
A key problem commonly seen in flood-irrigated fields is the damage that can be done at the tail end of fields that are furthest away from flood irrigation inflows. Often 50-200 feet of alfalfa can be damaged at the ends of fields, Putnam says.
A second benefit of SSDI, and somewhat related to the first, deals with irrigation timing. Drip allows for more timely irrigation sets whereas some “flood irrigation fields can take six to 10 days for water to get across the field,” Putnam says.
With SSDI, the field can be irrigated more evenly with water available to the entire field within hours, not days.
Putnam says a third SSDI benefit is the reduced wetting and drying processes in the soil based on cutting schedules. This can be particularly troublesome in heavy, clay soils that develop large cracks during the drying process, which can literally pull the roots apart. It can also be a problem on sandy soils where the soils dry out very quickly.
Flood irrigation leaves growers on a typical 28-day cutting schedule little choice for irrigation schedules, according to Putnam.
“You can irrigate once, maybe twice during the cutting period under a flood system,” Putnam says. “You typically cannot apply small amounts of water during that period, even if the crop only requires a small amount.
“We’re frequently deficit irrigating our fields because growers are skipping those small irrigation sets under flood,” he continued. “This is really bad for root development, which is why I think drip irrigation might be successful in increasing the yields.”
It is the more consistent availability of moisture over time that is likely to create conditions for higher yields.
The genetics of alfalfa reveal a yield potential approaching 16 tons per acre under the right conditions, Putnam says. The key is to provide the conditions in water, nutrient management, and harvest schedules to achieve these levels.
University data from controlled studies and farmer experience confirm SSDI can yield 20-30 percent more alfalfa compared to a flood irrigation system.
SSDI also tends to leave the soil surface dry which leads to less compaction and reduced weed germination, says Putnam.
Crop longevity can also be improved.
“We have observed longer stand life on SSDI fields due to the elimination of standing water on fields,” Putnam said.
SSDI can also improve delivery of fertilizers into the root systems. Attempting to add fertilizer on the soil surface through flood can pose problems with availability to the plant, Putnam says.
Rossow says he is currently applies compost materials collected from Wilgenburg Dairy as a soil amendment once or twice a year. He uses flood irrigation to move compost nutrients into the soil.
Lastly, there is a perceived idea that the volume of water used to irrigate alfalfa from SSDI can be reduced.
“I think the jury is still out on this one,” Putnam said. “Some growers are able to save water on some soils versus flood irrigation, but the main advantage is improved water use efficiency. More crop yield is obtained per drop of water applied.”
Rossow admits several challenges in his learning curve with SSDI, such as how deep to bury the drip tape and how wide to space the tape.
Rossow installed SSDI in his first 160 acres of alfalfa at a depth of 16 inches and 40 inches apart.
“The theory of going 16 inches with the drip tape was to get below where the gophers go,” Rossow said. “I won’t do that again.”
Newer fields have tape at 11 inches below the surface, which Rossow says has netted him “much better results” because it puts the water closer to the root zones and improves irrigation uniformity.
Putnam addresses distribution uniformity as one of the challenges because of differing soil types.
While generally a soil-specific determination, Putnam admits he is slowly coming to the conclusion that row spacings of less than 40 inches might be worth considering because of how water moves through the soil and away from the drip tape.
“With row crops you can irrigate within a root zone with subsurface drip; in the case of alfalfa as a broadcast crop you are probably losing yield through this corrugation effect we see between rows,” Putnam says. “This is something we are still learning about and is very soil-type dependent.”
Crop rotation patterns can also dictate how wide and deep SSDI needs to be placed. Alfalfa is commonly rotated with tomato on 40- or 60-inch beds, or with corn on 30-inch rows, which can be compatible with either 30- or 40-inch lateral drip spacings.
Rodent control is paramount. Rodent control and the maintenance of drip lines has been one of the major challenges for farmers. It is generally agreed that a year-round program of “zero tolerance” is necessary to make an SSDI system work.
Putnam suggests not completely abandoning flood irrigation methods in alfalfa, even with buried drip tape, for several reasons. This can include gopher control, soil salinity management and the ability to more effectively charge soil profiles with water during key times of the year.
For gopher control, Putnam admits that while flooding can help "it doesn’t solve the problem.”
Rossow hired an additional employee simply to address rodent control, which is done in part by using a pressurized carbon monoxide system.
“As far as poisoning gophers I have tried everything,” Rossow says.
Putnam says he has seen growers completely walk away from SSDI alfalfa because they could not get a handle on rodents.
“That is really the Achilles Heel of this type of system,” Putnam said.
When planting a new alfalfa stand and SSDI will be used, Putnam says sprinkler irrigation is necessary as part of proper stand establishment practices.
Dennis Hannaford, a product application specialist with Netafim, also recommends good ground prep, including a deep rip and addition of necessary soil amendments. Working the ground to get good seed-to-soil contact is important.
Planting at the right time is important too.
Alfalfa can emerge within 5-10 days if planted during warmer weather, Putnam says. This helps promote good root development. Putnam generally recommends planting alfalfa in September or October, depending on the region.
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Rossow says he likes planting new alfalfa between Aug. 15 and Sept. 1 in his area.
Conversely, planting too late – say November or December in the San Joaquin Valley – can result in additional weed pressure, poor root development, and reduced yields, said Putnam.