AgBioResearch

Hickory Corners, MI – As spring slowly advances across the Midwest, farmers are evaluating their fields of winter wheat and planning for this season’s fertilizer needs. The collective fertilizer decisions of wheat farmers across the globe has huge implications for the health of our climate.

Michigan State University (MSU) scientists together with scientists at the International Maize and Wheat Improvement Center (CIMMYT) in Mexico have been researching the effects of nitrogen fertilizer on greenhouse gases. According to a study out today, they validated past studies from Michigan showing that farmers can increase profits and radically reduce greenhouse gas emissions by applying fertilizer in more precise dosages.

One key difference: the farmers described in today’s study are from Mexico, not the US Midwest.

Published in the journal Agriculture, Ecosystems and Environment, the study shows that farmers in the Yaqui Valley, a major breadbasket region in northwestern Mexico, are applying significantly more nitrogen fertilizer than they need to maximize wheat yields.

Applying lower rates of nitrogen fertilizer would cut the region’s yearly emissions of nitrous oxide, a potent greenhouse gas, by the equivalent of as much as 130,000 tons of carbon dioxide. This is equal to the emissions of 14 million gallons of gasoline, according to Neville Millar, senior researcher at MSU’s Kellogg Biological Station (KBS).

This work builds on research started in 2000 at the KBS Long-term Ecological Research site in southwest Michigan on how different rates of nitrogen fertilizer applied to corn affected crop yield and soil emissions of nitrous oxide. On-farm experiments across Michigan showed that nitrous oxide emissions increased exponentially with increasing nitrogen fertilizer rates. That is, after enough nitrogen was applied to meet the needs of the corn crop, nitrous oxide emissions dramatically increased. But would this also be true in other parts of the world?

“The Mexico project took this experiment to the next level,” explains Millar. “This work validates the exponential increase in emissions for another important crop in one of the most important agricultural regions in Mexico.”

That has implications for more than just Mexico.

“Yaqui Valley wheat farming conditions and practices are similar to those of huge wheat cropping expanses in China, India, and Pakistan, which together account for roughly half of worldwide nitrogen fertilizer use for wheat,” notes study co-author Iván Ortíz-Monasterio, an agronomist at CIMMYT’s Yaqui Valley experiment station where the research was conducted. “The findings are thus globally relevant and represent a potential triple win, in the form of reduced greenhouse gas emissions, higher income for farmers and continued high productivity for wheat cropping.”

Millar and the international team of scientists measured nitrous oxide emissions and tracked yields and grain quality of spring durum wheat crops during two growing seasons.

“In our study, applying 145 kilograms of fertilizer per hectare (~130 lb/acre) resulted in the optimum wheat yield,” said Millar. “Yaqui Valley farmers typically apply around 300 kilograms (~270 lb/acre). The wheat crop takes up and uses only about a third of that nitrogen; the remainder may harm the environment as nitrous oxide or nitrate, which can contaminate groundwater.”

Importantly, there was no reduction in the quality of the wheat at the 145-kilogram fertilizer rate.

Promoting profitable, climate-friendly fertilizer use

Farmers’ excessive use of fertilizer is driven largely by risk aversion and economic concerns, according to Ortíz-Monasterio. “Because crops in high-yielding years will require more nitrogen than in low-yielding years, farmers tend to be optimistic and fertilize for high-yielding years,” said Ortíz-Monasterio. “At the same time, since farmers do not have data about available nitrogen in their fields, they tend to over-apply fertilizer because that is less costly than growing a crop that lacks the nitrogen to develop and yield near to full potential.”

Part of a research partnership between CIMMYT and the KBS LTER to help intensive farming be more climate friendly, one goal of the present study was to gain a more accurate picture of nitrous oxide emissions in Mexican grain crops.  

“The information from this study can be incorporated into carbon market programs that would pay farmers for applying nitrogen fertilizer more precisely” Millar said. There are already fertilizer reduction programs available in several carbon markets, and the first credit for reducing fertilizer (and thus nitrous oxide emissions) was issued to a Michigan farmer in June 2014.

“This study shows that low emissions nitrogen management is possible in tropical cereal crop systems and provides important guidance on the optimal levels for large cropping areas of the world,” Lini Wollenberg, an expert in low-emissions agriculture for the CGIAR Research Program on Climate Change, Agriculture and Food Security (CCAFS), said. “With this improved understanding, countries will be able to better plan and implement their commitments to reducing emissions.”

Additionally, information from studies like this can be used by advisors and policymakers to develop improved management recommendations and incentives for farmers.

“We never imagined, a decade ago, where this project would lead” concludes Phil Robertson, MSU Distinguished professor in the Department of Plant, Soil and Microbial Sciences and a co-author of the work. “Being able to leverage our work in Michigan, collaborate with Mexican colleagues and help to inform international climate goals has been a rewarding experience for our KBS LTER team.”

To read the article:

Millar, N., A. Urrea, K. Kahmark, I. Shcherbak, G. P. Robertson, and I. Ortiz-Monasterio. 2018. Nitrous oxide (N2O) flux responds exponentially to nitrogen fertilizer in irrigated wheat in the Yaqui Valley, Mexico. Agriculture, Ecosystems and Environment, https://doi.org/10.1016/j.agee.2018.04.003.