For Erdman Farms in the middle Sacramento Valley, planting spring wheat was simply part of a field’s 5-year rotation of cover crops to benefit the soil.
But then the operation discovered that it could make some money from the grain, grower Kim Gallagher says.
The breakthrough came after Gallagher agreed to use a section of her field for a University of California Cooperative Extension experiment on efficient nitrogen management, she says.
Last season, instead of applying the full nitrogen load at planting as many growers do, the farm began with a partial application and then used monitoring to determine in-season fertilization according to the plants’ need.
The resulting crop was “bin-busting,” Gallagher told about 20 other growers during a recent UCCE-sponsored workshop in her field. “It was the biggest yield we ever had.”
So this winter, the farm planted wheat again and is using the same in-season nitrogen management regimen.
“It’s cost-effective for us,” Gallagher says. “It’s an efficient way to use nitrogen at the right time.”
With concerns over nitrate leaching into groundwater on the rise, the UC in recent years has been touting the use of a “nitrogen-rich strip” – a segment of field over which a grower made a double or triple pass at the beginning of a season. This provides a benchmark with which to compare the rest of the field, upon which less nitrogen is applied at the start.
As the season progresses, growers periodically test soil and plants to determine whether they need to add more nitrogen, which can be topdressed shortly before an expected rainstorm.
This practice is particularly beneficial in rainy winters, when crops’ nitrogen loss is higher because the mineral seeps with water away from the root zone, advisors say.
In the case of wheat, “the demand for nitrogen is right now,” says Mark Lundy, a UC-Davis small grains specialist. “The crop is growing.”
As of mid-March, Lundy estimated that the wheat in Gallagher’s field had taken up about 40 percent of the season’s nutrients. Within a few weeks, it’ll be 80 percent finished, he told growers during the workshop.
The wheat industry is among numerous commodities in California grappling with how to achieve maximum efficiency with nitrogen, which is critical for crop growth but has been determined to pollute drinking water in some areas.
In nature, nitrogen cycles through soil, water and plants at low concentrations, but agriculture needs high nitrogen input to produce profitable crops, the UCCE explains in a training course for crop advisors.
Nitrate – an anion consisting of a single nitrogen atom bonded with three oxygen atoms – is not retained in soil and moves with water, eventually reaching the aquifer, scientists explain. Thus, areas with shallow groundwater tables and intensive agriculture are most vulnerable to contamination, according to the university.
Nitrate pollution in groundwater is a widespread problem that can pose serious health risks to pregnant women and infants if consumed in concentrations above the maximum containment level of 45 milligrams per liter, warns the California Water Resources Control Board.
Contamination has occurred in many areas of California, but the worst concentrations are found in the San Joaquin Valley’s Tulare Lake Basin and the Salinas Valley, according to the water board.
Removing nitrates from water is an involved and expensive process. But in 2008, state legislators passed a bill ordering the water board to develop projects to curb the ongoing pollution in the two most severely affected valleys. Meanwhile, the board in 2010 contracted with UC-Davis to conduct an independent study of nitrates in the two valleys, which the university delivered in 2012.
While the Salinas Valley is dominated by field crops such as berries and vegetables, the Tulare Lake Basin is the state’s most lucrative agricultural region and hosts a variety of crops, including citrus, tree nuts and annual plantings.
In these areas, the scientists identified agriculture as the source of nearly all the nitrogen present, with synthetic nitrogen accounting for 54 percent and dairy manure adding another 33 percent.
Of the total nitrogen inputs in the two valleys, only 37 percent is removed at harvest, while 51 percent remains in the soil as leachable nitrate, according to the UC study.
Further, the report asserted that nitrate pollution in aquifers will probably worsen, as most nitrate detected in groundwater today was applied to crops decades ago.
Among its resulting actions, the Legislature established a groundwater monitoring program that uses funds from waste discharge permits obtained by growers. The state also worked with the UC to set up a nitrogen management training program for certified crop advisors, which will have an estimated 800 graduates by 2025, according to the water board.
Under the Irrigated Lands Regulatory Program, all growers who irrigate commercial crops must either join regional coalitions or meet waste discharge permit requirements individually, which is considerably riskier and more burdensome, UC advisors say.
In the Central Valley, coalitions handle groundwater quality assessments and plans, monitor long-term water quality trends, promote best-management practices to protect groundwater quality, compile data submitted by growers and submit the information to the water board, according to the UC’s crop advisor training materials.
Growers are responsible for annual farm and nitrogen management plans, which they send to their coalition or directly to the water board. The nitrogen plans must be certified if the field is in a high-vulnerability area.
California agriculture has a long history of nitrogen use, with cropped acreage, fertilization rates, dairy production and irrigated land increasing in the last 50 years, UC advisors say. Extension experts have been emphasizing to growers that inefficiency of irrigation and nitrogen application leads to nitrate leaching issues.
Measures to increase efficiency largely vary by commodity. For instance, many growers fertigate through drip irrigation systems near the plants’ or trees’ root zones. But in spring wheat plantings, even growers with irrigated fields typically aren’t watering in late winter, when the plant’s tillering stage brings the best opportunity for uptake.
Growers have typically applied nitrogen at planting and hoped it would last through the season. But in rainy winters like 2018-19, much of that nitrogen washes away. And a few growers lost their crop this season as their fields were waterlogged by flooding, says Sarah Light, a UCCE agronomy advisor.
SAVING ON COSTS
Light appeals to growers’ desire for profitability as well as sustainability.
“Fertilizer is a large part of the cost of wheat production,” she says. If a farm only applied one-third of its normal load at the beginning and the crop failed, it would still have two-thirds of its investment, she says.
In UC field trials in a large number of locations, the yield and protein benefit of applying nitrogen fertilizer from the tillering to jointing stages has been consistent and reliable, the university explains in a newsletter for wheat growers.
In the trials, tillering applications resulted in an overall 10 percent increase in yields and slight increases in protein compared to the pre-plant application of an equivalent amount of fertilizer, as more of the nitrogen was drawn up into the plant.
At the workshop on Gallagher’s farm, Light and Lundy demonstrated how to test soil nitrogen levels in a water solution and how to use hand-held devices to monitor plants.
“The take-home message is that because the nitrogen cycle is complex, the best opportunity to reduce it is to improve our nitrogen use efficiency,” Light says.
Gallagher has become a believer.
“All these methods have been super helpful for me,” she says.