(Beyond Pesticides, February 2, 2018) California regulators may be drastically underestimating chemical-intensive agriculture’s contribution to nitrogen oxide (NOx) caused air pollution, acid rain, and respiratory illness in the state, according to a new study published in Science Advances by researchers at University of California, Davis. While NOx pollution is usually associated with energy production and vehicle emissions, fertilizer use on crop fields is contributing to significant air pollution problems. Advocates say that the study is an urgent call for farmers to eliminate dependency on soluble, synthetic, nitrogen-based fertilizers and adopt the use of insoluble soil amendments that support soil biology that provide plants with nutrients.
NOx gasses are major sources of pollution in the U.S. and throughout the world, and include the compounds nitrogen oxide (NO) and nitrogen dioxide (NO2). Chemical-intensive, synthetic nitrogen fertilizers are applied in a form that is readily available to plants, while organic nitrogen fertilizers require the biological life in the soil to break down the fertilizer into a form that plants can use. These nitrogen fertilizers that are not immediately taken up by plants can cause pollution problems. Natural nitrogen in the atmosphere must be transformed to be able to be used by organisms as a source of nutrients through a range of biological factors in the soil. However, the pollution associated with the production of synthetic fertilizers that requires petroleum or natural gas, increasingly from fracking, and the introduction of synthetic nitrogen and other pollutants into the atmosphere contributes to environmental degradation, asthma, and other public health problems..
While some fertilizer not taken up by crops will eventually turn into harmless nitrogen (N2), other amounts can become hazardous nitrogen oxide gasses. Once out of soil and into the atmosphere, NOx gasses react with moisture, sunlight, and other chemicals to form pollution. The gasses can combine with other chemicals in the air to form particulate matter able to deeply penetrate and harm human lungs, create acid rain when interacting with water, and form haze that decreases visibility. A 2014 report from the World Health Organization indicates that 1 in 8 total global deaths, around 7 million people each year, die prematurely as a result of exposure to air pollution.
The results of this study stand in stark contrast to the state’s current estimation of NOx emissions from farmland soil. While the California Air Resources Board (CARB) indicates only 3.8% of NOx air pollution comes from croplands, researchers determined that the contribution may in fact be between as much as 20 to 51%.
The study suggests that the state’s methodology for recording cropland emissions may be at fault. CARB measures emissions using data obtained from farms only within 125 miles of Sacramento, thus failing to record higher NOx levels that emanate from areas with more intense agricultural production, such as California’s Central Valley.
Researchers took both a “top-down” and “bottom-up” approach to measuring NOx emissions. As part of the “top-down” approach, planes outfitted with scientific equipment took measurements of NOx emissions over California’s San Joaquin Valley, between Fresno and Visalia, a hotbed for agriculture and an area where some of the highest amounts of nitrogen fertilizer is applied. As part of the “bottom-up” approach, researchers compared results seen from direct measurements over the San Joaquin Valley to a model developed for the same region. The model created by researchers produced estimates only slightly higher than those discovered via plane measurements. Researchers then looked at NOx emissions compared to nitrogen application rates recorded by the state of California and the U.S. Department of Agriculture, finding that high rates of nitrogen fertilizer use in lined up neatly with high levels of NOx emissions.
Researchers determined that temperature, soil moisture, and the amount of nitrogen applied are the most significant factors in whether a soil will release NOx or inert forms of N2. Higher temperatures, more arid soil, and higher nitrogen fertilizer application rates act as the greatest risk factors for NOx emissions. However, the UC Davis scientists provided a range of suggested practices that farmers can implement to reduce harmful emissions. Lower application rates and precision fertilization, rather than broadcast applications, can help reduce excess nitrogen input into soils. Cover crops, and the creation of riparian areas around farmlands can help absorb residual nitrogen. Greater attention to irrigation practices can also ensure that inorganic nitrogen in the soil is not converted into nitrogen oxides. In organic farming systems, the nurturing of microbial activity in the soil food web (a feed-the-soil system) produces slow release nutrients including nitrogen that is taken up by he plants.
With population continuing to increase lock-step with demand for food, unless measures are taken to conserve nitrogen use, this trend is likely to accelerate. The good news is that many of these practices that support the soil food web are already being used on certified organic farms. And given the significance of this study, conventional farmers have a greater incentive to implement them as well. Speaking with the Fresno Bee, Jim Houston of the California Farm Bureau Federation said, “Farmers have a long history of adjusting their practices in response to emerging science, and we will watch to see if further studies verify the results reported here. It’s important to note that most of the steps the study suggests are already underway. Farmers want to use the appropriate amounts of fertilizer and have long relied on expertise from the University of California in making those applications.”
While the study focused on agricultural applications of nitrogen, imprudent use of the fertilizer on garden, lawns, and landscapes also can represent a significant source of non-point nitrogen pollution. For these areas, focus first on cultural practices, and if fertilizer is needed based on a soil test, use Beyond Pesticides list of organic certified fertilizers to choose a soil amendment that, in an organic system, is not likely to result in pollution problems. And to support a healthier future for farming and safer, cleaner air for those living in and around agricultural communities, support organic practices by buying organic.
All unattributed positions and opinions in this piece are those of Beyond Pesticides.