The good news is that lignin, a natural polymer and constituent of cell walls of plants, helps them stand up much as the rebar in a skyscraper does.
The bad news is that high lignin content makes plants less digestible for cattle.
Two researchers talked of the tightropes they must walk in balancing lignin’s role during this year’s Alfalfa and Forage Field Day held at the University of California (UC) Kearney Agricultural Research and Extension Center (KARE) in Parlier, Calif.
Dan Putnam, UC agronomy and forage specialist at UC Davis, weighed in on the challenge of timing alfalfa harvests to maintain its quality. A later harvest can bring greater tonnage but less digestibility as lignin increases.
One solution studied is the use of HarvXtra, a genetically engineered alfalfa, which has higher yields while maintaining lower lignin. Another is the HiGest line, which is not genetically modified, but is more similar to conventional varieties than HarvXtra.
Putnam said it is important to consider whether countries that buy U.S. alfalfa approve of genetically engineered crops.
He said that in most years a grower makes more money choosing the highest yielding varieties over varieties that yield less but perhaps produce higher quality hay.
Jeffrey Dahlberg, KARE director, said brown midrib sorghums were developed in the 1970s, a mutation that lowers the lignin content. Researchers continue to look for ways to keep plants with brown midrib from lodging, basically falling over, including adding a gene that shortens internode length.
Dahlberg said the Kearny Center is “the perfect place to study drought stress.” He’s flying a drone over a 6.2 acre research plot that houses 600 lines of sorghum. The drone can measure plant height, biomass, and stress in a fraction of the time than a crew on the ground could.
Cousins and uncles
Putnam is also looking at the use of drip irrigation in alfalfa. Currently, about 2 to 3 percent of the alfalfa grown in California is under subsurface drip.
Drip advantages can include better water distribution over space and time. With flood irrigation, it’s difficult to work in multiple irrigations during the brief hay-growing season of about 28 days.
That’s not the case with drip. Putnam sees water saving potential with drip to cut soil evaporation and runoff. Drip also prevents wetting and drying cycles that can damage roots in heavy soils. And it should provide longer potential stand life and less weed pressure.
But Putnam warns that it’s a major challenge to manage gophers which damage drip systems.
“Some growers have walked away from large investments due to rodent infestations,” he said.
Subsurface drip provides an ideal habitat for gophers.
“They’ll call their cousins and uncles and have a party there,” Putnam said. “You have to take a no-holds-barred approach to them.”
Due to the risk of gophers, he recommends keeping flood irrigation as an option in case drip lines are compromised.
Kurt Hembree, UC Cooperative Extension (UCCE) weed management farm advisor at Fresno County, discussed the importance of using “burn down sprays” on weeds in a timely way. He warned that there are a number of weed species now tolerant or resistant to glyphosate, including junglerice, Palmer amaranth, horseweed, and hairy fleabane.
It’s important, he says, to manage areas bordering fields, including canal and ditch banks, where “weed seed reservoirs” thrive. Preemergents can also play a key role in weed control.
When using herbicides, Hembree says switch modes of actions, varying chemicals applied to not foster resistance.
Protect chemical use
Addressing pest management including the alfalfa weevil was Rachel Long, UC agronomy and pest management advisor in Sacramento, Solano, and Yolo Counties. She says one challenge is the limited number of chemicals available for use in alfalfa to fight the weevil. It basically comes down to organophosphates and pyrethroids.
In some areas, notably the Intermountain region, the weevils are resistant to the latter, and Malathion does not prove effective as well. Moreover, some species of the weevil are not susceptible to biological controls.
“It’s important to protect the chemicals we have,” Long said.
She says keeping pests out of alfalfa is important, taking such steps as crop rotation, a level seed bed, planting early in the fall, good plant health, cleaning equipment between fields, using certified seed, selecting pest and disease resistant varieties, plus monitoring and recording pest and beneficial insects for economic threshold levels.
Long added that grazing or sheeping-off alfalfa during the winter can reduce weevils, along with over-seeding clovers or grasses.
Other pests include armyworm and alfalfa caterpillars, aphids, cutworms, leafhoppers, the three-cornered alfalfa hopper, ground mealybug, clover root curculio, and spider mites.
Last year, the sugarcane aphid arrived in California for the first time causing considerable damage to forage sorghum. This year, it appears to be less of a threat, judging from comments solicited from the field day audience by Nicholas Clark, UC agronomic cropping systems and nutrient management advisor for Kings, Tulare, and Fresno counties.
Clark asked about pest status in the central San Joaquin Valley. A pest control advisor who works in Merced and Madera counties said it appears to be less of a threat than it was last year. Another field day participant said the pest “came on heavy” in the Five Points area.
Dahlberg said some growers made the mistake of spraying for corn earworm which wiped out beneficial insects.
“That was like opening the buffet table,” he said. “The sugarcane aphid gives birth to a live female that’s pregnant and delivers babies nine hours after it’s born. Don’t spray for corn earworm on sorghum.”
Clark said it is important to monitor for the aphid. One effective way of combating it is to use neonicotinoid seed treated for resistance against it. Imidacloprid- or clothianidin-coated seeds have been shown to offer protection for up to 40 days after planning.
Clark said the aphid reproduces on sorghum, Sudan, sorghum-Sudan and Johnsongrass. It feeds but won’t reproduce on corn. It will not feed on small grains.
Damage from the pest includes honeydew production and sooty mold growth, reduction in sap flow and dryer leaves, and plant death.
Clark said planting as early as possible is important to cut the aphid threat, along with controlling Johnsongrass as an alternative host.
He also advised to avoid chlorpyrisos, dimethoate, and malathion when possible to protect natural enemies.
Bob Hutmacher, UC Cooperative extension specialist with UC Davis and director of the West Side Research and Extension Center, looked at irrigation and nitrogen fertility management in forage sorghum and corn.
He found some evidence that eliminating or reducing early season irrigations reduced yield more than the elimination of late season irrigations.
Dan Munk, UC farm advisor for Fresno County, talked of irrigation and salinity management in forage production. He said native salts contribute to salinity, along with fertilizer, composts, and irrigation water.
It’s important, he says, to do water analysis to ascertain its quality. Lowering the pH of irrigation water can increase water penetration and improve mineral nutrition. Adding calcium can also increase water penetration and improve soil structure. Leaching with high quality irrigation water can erase years of salinity buildup.
Marsha Campbell-Matthews, UC agronomy advisor Emeritus with Stanislaus County, discussed the best ways to optimize surface irrigation in high flow systems, including shortening the runs, increasing slopes, increasing the flow rate so water moves faster, and making the soil surface smoother.
She said a higher flow rate was better than a steeper slope, and doing both was the best “but difficult to manage.” Basically, she explained, the water moved so quickly by using both options that it was hard to time the applications.