Ammonia emissions from fertilizer applications in California's Central Valley can be measured and are less than estimated by air quality regulators, according to a researcher at California State University, Fresno.

Charles Krauter, coordinator of air quality programs at the Center for Irrigation Technology, says his observations show ammonia emissions from farming to be about 2.5 percent of the total, not the 5 to 10 percent previously estimated by the State Air Resources Board.

Krauter, who is also a professor of soils and irrigation at CSU, Fresno, presented the findings at a recent conference in Salinas held by the Fertilizer Research and Education Program (FREP), which funded part of the research.

The air resources board's assumption several years ago, Krauter said, was that all the ammonia in the atmosphere of the region was due to fertilizer applications and reductions in ammonia would have to come from lowering fertilizers use.

“We think we have developed some good information,” he said. “We started this project because the state board realized it had a very tenuous estimate of ammonia coming from fertilizer applications. This had many in the agricultural industry understandably spooked.”

The board, he added, probably knew the estimate of 5 to 10 percent was too high, but it had very little science — and basically none done in California — to quantify the level and show how to reduce it.

The board funded a project by scientists at NASA's Ames Research Center at Palo Alto, who in turn asked Krauter to lead the field research on fertilizer use in Central Valley counties from 1999 to 2002.

Field data input

Field data from Tulare County to southern portions of Merced County were put through a statewide atmospheric computer model at Ames to reach the figure of 2.5 percent.

The database, Krauter explained, included crop acreage and locations by counties, soil information, and fertilizer application amounts and methods. Crop acreage data came from the California Department of Water Resources.

“Fertilizer applications were not available from any public source, so data was estimated by questioning farmers, fertilizer industry members, county farm advisors, and other crop specialists,” he said.

Although practices varied across the state, they could be correlated with the county-based crop acreage data. The database was used to estimate the application of various types of nitrogen fertilizers to the crops of the state.

Finally, these estimates were checked, Krauter added, by comparing them with the public records of fertilizer sales from the California Department of Food and Agriculture.

SJV emissions

The study found that the San Joaquin Valley accounts for just over one-half of the state's total annual emissions of ammonia directly traced to agricultural application of fertilizers.

“On the basis of DWR crop types, it appears that the generalized categories of field crops and truck crops each account for about one-third of the state's total annual emissions of ammonia, directly from chemical fertilizer sources.

“Grain, pasture grass, and rice crop categories also contribute large fractions of the state's total annual emissions of ammonia, directly from chemical fertilizer sources,” Krauter reported.

He said ammonia is the dominant gaseous base in the atmosphere and may control, when combined with alkaline soil dust, the acidity of rain. It may also react with other chemicals in the air to contribute to airborne particulate matter.

Variable rate product

His studies measured the ammonia from fertilizer applications, taking into account the effects of time of day, crop type, and other environmental factors. As an added step, the project attempted to measure the effects of variable rate nitrogen applications on ammonia emissions.

“Variable rate fertilizer decreases the net loss of ammonia volatilized, as less fertilizer is applied when compared to a blanket application at a high rate,” he said.

Use of variable rate applications reduces both input costs and the environmental impact of the possible over-application of fertilizers.

“New applications of variable rate technology must be investigated for benefits such as those observed in this study,” he said.

The research team for the ammonia emissions project included Dave Goorahoo, Matt Beene and Barry Goodrich of the Center for Irrigation Technology at CSU, Fresno and Christopher Potter and Steven Klooster of the Ames Research Center.

Krauter is continuing research with FREP funding on follow-up ammonia measurements and is also involved with studies of dairy emissions.

Runoff challenges

In another FREP project detailed at the Salinas conference, William R. Horwath of the Department of Air, Land and Water Resources at the University of California, Davis, concluded there are challenges with the use of conservation tillage and cover crops to reduce agricultural runoff and decrease nutrient losses.

His studies were done at UC, Davis and in fields of grower-cooperators in the Sacramento Valley.

“Adherence to strict conservation tillage practices can immediately reduce fuel costs, but the potential benefits to water quality may take years to realize,” he reported.

He went on to say “in the short term, growers may have other water conservation options, including reconfiguring fields to reduce runoff velocity, and thus erosion.”

Horwath said, on a farm scale, cover crops significantly reduce winter runoff but also may affect subsoil water recharge and soil moisture content at the time of planting.

Noting that additional research is necessary, he said, “The potential for winter cover crops to alter the water budget of subsequent crops under furrow irrigation systems poses important questions, considering future water supply concerns.”

Created in 1990 under the California Food and Agriculture Code, FREP uses the mill tax on fertilizers sold in the state to provide grants for studies to minimize environmental impacts by finding cost-effective ways to improve the efficient use of fertilizers.