In a study published Wednesday in the research journal Science Advances, a team led by UC Davis says agricultural soils contribute 25 to 41 percent of nitrogen oxide emissions in California. Natural soils emit nitrogen oxide, too, but the concentration is far higher in fertilized cropland, the researchers wrote. Nitrogen oxide (NOx) is a major factor in smog formation.
Importantly, the study states that NOx emissions vary temporarily, with the largest emissions spiking when fertilizers are applied. The study further states that their model validation was restricted to a “handful” of empirical studies, thus calling for the need for more ground measurements throughout CA to better assess the impact and spatial distribution of soil NOx emissions. It is important to note that the results of this study have not been peer-reviewed or duplicated to assure the validity of the results. A wide range of universities and regulatory entities have been researching agricultural areas for an extensive period of time and not found agricultural lands to be significant contributors of nitrogen oxide.
The study suggests potential solutions for reducing NOx soil emissions, primarily through different forms of fertilizer management. Growers work closely in conjunction with UC Integrated Pest Management advisors when applying fertilizer for best management practices. Many of these practices are already in use by farmers in California, representing a change for the better from historical practices that have contributed to current groundwater nitrate levels.
When it comes to the beneficial effects citrus trees have on pollution, a University of California study shows that air quality can benefit from citrus trees. In the study conducted by Dr. Karlik of the University of California Cooperative Extension, Bakersfield, citrus trees have been found to positively contribute to air quality in the Central Valley. Citrus acts as a sink for the deposition of ozone and other trace gases. On an annual basis, citrus trees absorb an estimated 9,000 tons of ozone. A single orange orchard contributes up to 40% of the total ozone removal.
Varied members of agriculture in the San Joaquin Valley have communicated their displeasure with the Dean of Agriculture. A meeting last Monday occurred in Fresno in which several Ag groups devised a strategy to push back and strongly suggest to the Dean that further communications on this alleged science will require major media response that could only damage relationships. CCM has sought, and the Dean has responded favorably, to a meeting with interested parties. CCM is also working closely with California Cotton Growers & Ginners and Western Plant Health Association on talking points refuting the comments in the report. Others have contacted members of the Air Board, CDFA, and California Energy Commission to respond with previously published reports, thereby pointing out the flaws in the UCD document.
Scientists at other institutions have begun to weigh in via requests from property owners and sister organizations. “A replica of the Harter Groundwater Report fallout is what we want to avoid,” states CCM President Joel Nelsen. “Op-Eds are being submitted, letters to the editor being forwarded, and phone calls are being made.” UC Davis has been urged not to “market” this report as was done previously by Thomas Harter.