By Bob Johnson, Ag Alert
As dairy farmers endure the worst drought in decades, University of California Cooperative Extension researchers are offering tips on making every drop count—from deficit-irrigation strategies for feed crops to check lists to reduce water waste from leaky hoses and nozzles.
Most dairies rely on surface water that is being severely limited this year and on pumping from underground aquifers that are suffering from overdraft.
While there are opportunities to save water at most dairies, researchers say the greatest conservation opportunity is in irrigation of forage crops that feed the cows.
“The animal side is a glass in the proverbial bucket of water used to grow forages,” said Deanne Meyer, a UCCE specialist. “Growing forage uses water, and irrigation or crop growth is the larger of the two items.”
No feed crop is more important than corn, as the large majority of the 10 million tons harvested annually statewide for silage goes to dairies.
“Corn is not drought tolerant. Any reduction in irrigation will reduce yields,” said Konrad Mathesius, a UCCE farm advisor in Yolo, Sacramento and Solano counties. “However, the impact of drought stress differs depending on when it occurs in the crop’s growth cycle.”
A 5% to 10% reduction in water is generally a good trade-off, which adds up over the 400,000 acres of corn silage grown in the state. Mathesius said the best time to reduce corn irrigation with a minimum of crop loss is late in the season, once the crop has matured.
“Irrigating after the crop is mature is most likely wasted water,” Mathesius said. “In silage corn, the plant is considered mature at 50% milk line. In grain corn, maturity is indicated by a black abscission layer.”
He said the worst time to try to save corn irrigation water is amid a crucial period near the middle of the growing season, when the yield penalty can be substantial.
“Any reduction in irrigation will lead to a reduction in yield, but that stress at some points of development can lead to massive yield reductions,” Mathesius cautioned. “Two weeks before and after tasseling is critical to ear formation, and ears account for 50% of silage weight.”
He said prolonged stress during tasseling and ear formation has been cited to cause anywhere from 34% to 95% reductions in yield.
UCCE grain systems specialist Mark Lundy produced a report, “Managing Irrigated Corn during Drought,” that outlines ways to optimize returns from limited water resources. It may be found online at anrcatalog.ucanr.edu/pdf/8551.pdf.
Researchers say water-deficit strategies for all field crops need to account for the varying amounts of moisture in the ground before irrigation.
“A coarse-textured soil, that is, sandy soils will generally have lower soil moisture than a fine-textured soil regardless of whether we’re in a drought,” said UCCE farm advisor Michelle Leinfelder-Miles. “Soil texture can vary across farms and even across a field and this can result in variable soil moisture across a field.”
If drought conditions continue, another alternative is to plant short-season corn varieties later in the growing year because they take less water.
“A rough estimate is that you can save about 1-acre inch of water for every 1-ton difference in yield potential between a short- and long-season variety,” Mathesius said. “The season is shorter, so the crop requires less water to go to maturity.”
He said short-season varieties typically produce lower yields and therefore need less water. Also, the evaporative losses from the soil don’t have as much time to remove soil moisture.
“The crop spends less time in the ‘danger zone’ of the reproductive phases, so growers won’t face as much of a yield threat for as much time,” Mathesius said. “Growers should be cautious about choosing short-season corn that has been tested for our Mediterranean climate.”
In recent years, more growers have shown interest in sorghum, a water-resilient relative of corn with a superior ability to mine the soil for moisture. Sorghum is also an important livestock feed.
“Sorghum productivity in tons of total biomass per unit of applied irrigation water has been shown to be significantly higher than corn,” said Bob Hutmacher, UCCE researcher. “In the San Joaquin Valley environment with typical planting dates in May or June, total crop water use—irrigation plus water extracted from the soil—would total in the range of about 19 inches to about 26 inches for a long-season, later-maturing type.”
For such varieties, he said, “the harvest can extend into late fall due to indeterminate growth habit.”
But the sorghum water use is significantly less than what it takes to grow a full crop of corn for dairy feed.
Meanwhile, Leinfelder-Miles said, “the corn needs approximately 25 to 29 inches, but the system may need variable amounts depending on irrigation system, soil characteristics and climate.”
She added, “We would estimate a higher amount of water in order to achieve 100% yield potential, depending on the system characteristics, and a 36- to 41-inch estimate takes these things into account.”
While sorghum uses less water than corn, an efficient deficit irrigation program depends on which type of sorghum farmers are growing, Hutmacher said.
“In assessing likely sorghum responses to reduced water applications,” he advised, “consider the diversity across sorghum types in characteristics such as rooting density/depth, days to harvest and growth habit from forages—ranging from multi-cut Sudan grass to one-cut tall photoperiod responsive types, multipurpose types with significant grain heads or brachytic types.”
As with corn, there are times during the growing season to avoid stressing sorghum.
“You can get away with delaying first or second irrigations, particularly if planting longer-season photoperiod sensitive types. Stress should not be so severe as to affect seedling survival and root establishment,” Hutmacher suggested. “Avoid severe stress during late panicle differentiation through flowering if growing a multipurpose-type forage where grain yields are an important part of yield/quality.”
If growers successfully thread the needle, it is possible to get more crop per drop with a sorghum deficit irrigation program.
“With some care to avoid stressing the crop during the growth stages where growth and yields are most sensitive to water deficits, it is possible to save 2 or 3 inches of water with very little impact on forage yields, maybe less than 5% to 10% yield reduction,” Hutmacher said.
Deficit irrigation saves water, but it may be worth testing for excessive nitrate levels in many feed crops, particularly if moderately high rates of nitrogen fertilizer were applied, he added.
Sorghum species such as Sudan grass are particularly prone to high nitrate accumulation, according to an article by Mathesius, Lundy, UCCE farm advisor Josh Davy and Gabriele Maier of the UC Davis School of Veterinary Medicine.
“Even crops such as oats, barley and wheat can have excessively high nitrate concentrations in normal years, let alone drought years such as this,” they wrote in the UC Small Grains Blog in April. “Weedy fields also tend to have much higher levels of nitrate. When in doubt, test for nitrates.”
Meanwhile, water used at the dairy may be a glass in the bucket compared to irrigation. But Meyer said it still offers opportunities for conservation.
“Check and replace leaky drop hose sprayers in the parlor,” she advised. “Turn off floor hoses when not in use; they can put out over 10 gallons a minute. Evaluate soaker and sprinkler nozzles daily. A broken nozzle emits far more water than a functional one. And are there any cows standing at the mister line at midnight?”
Even with all conservation measures implemented, there may still not be enough water and feed to support all the animals. That may lead to difficult decisions on thinning herds.
“Culling decisions should maximize the profitability for the herd and eliminate animals that utilize resources inefficiently,” advised Randi Black, UCCE dairy advisor in Sonoma, Marin and Mendocino counties.
“It’s important to determine how many animals you will be able to support during the drought,” Black said. “Understanding the cost and supply of feed and water resources projected over the next six months to a year will create a starting point of how many animals your resources may support.”
