Crop output boosts soil nitrous oxide emissions, according to computer simulations.


The greenhouse gas nitrous oxide emissions from soils have grown during the previous century, according to a computer modelling study. The newly released study discovered that since 1900, the expansion of agricultural acreage and extensive fertilizer inputs have mostly driven an overall increase in nitrous oxide emissions from U.S. soils.

To feed the model and quantify variations in nitrous oxide emissions from soils in the United States, the researchers used huge amounts of data on everything from weather patterns to soil conditions to land use and agricultural management techniques. The findings, which were published in the peer-reviewed academic journal Global Change Biology, break down soil emissions by ecosystem types and major crops, finding that the expansion of agricultural land since 1900, as well as intensive fertilizer inputs, have largely driven an overall increase in nitrous oxide emissions.

According to Chaoqun Lu, associate professor of ecology, evolution, and organismal biology and the study’s corresponding author, using such ecosystem models to determine the origins of nitrous oxide emissions could benefit policymakers in enacting conservation measures and responses to climate change. “We’re utilising a process-based ecosystem paradigm,” Lu explained. “It’s analogous to simulating an ecosystem’s patterns and processes on our computer. We use algorithms to mimic how natural systems respond to changes in climate, air composition, and human activities by dividing land into thousands of uniformly sized pixels.”

The results suggest that emissions have increased

Nitrous oxide emissions from U.S. soil have more than tripled since 1900, from 133 million metric tonnes of carbon dioxide equivalent (MMT CO2 eq) per year at the turn of the century to 404 MMT CO2 eq per year in the 2010s, according to the study. According to the report, agricultural soils are responsible for about three-quarters of the increase in emissions, with corn and soybean cultivation accounting for over 90% of the increase in ag-related emissions. The study authors noted in their report, “Our study implies a large [nitrous oxide] mitigation potential in farmland and the need of exploring crop-specific mitigation strategies and prioritising management approaches for targeted crop varieties.”

According to Lu, the increase in emissions is due to the expansion of agriculture in the United States. According to the computer models, farmed land generates more nitrous oxide than wild landscapes. According to Lu, this is largely owing to the widespread use of nitrogen fertilisers on agricultural land and legume crop output. The additional nitrogen is utilised in part by crops, with the remainder remaining in soils or being lost to the environment. Microorganisms in soil eat nitrogen-containing substances and produce nitrous oxide as a byproduct during this process. According to Lu, a better understanding of the dynamics of which crops produce the most emissions will assist define climate mitigation strategy. Because maize requires more nitrogen fertiliser than other crops, the study discovered that soils where corn is planted generate more nitrous oxide per unit of fertiliser used, according to Lu.

Mathematical models that simulate natural processes were created by the researchers. According to Lu, the models are based on mountains of data acquired and built over many years. Government data on crops, land use, weather, and other variables was collated by the researchers. Farmers and other landowners’ historical and survey data were also taken into account.

In order to validate their findings, the researchers matched the outcomes of their model to real-world data. For example, the scientists demonstrated that their model’s production projections matched national yield data for important crops such as corn, soybean, wheat, rice, and others dating back to 1925. This demonstrates that the model simulation was able to trace the long-term trajectory of nitrogen intake, which has supported growing crop yield over the last century. They then compared their model’s nitrous oxide emission projections to real-world data from a variety of natural and managed soils around the country, as well as seven-year time-series measurements from a central Iowa corn-soybean rotation site.

“Our group has spent a lot of work enhancing model performance and building the driving force history for the model simulations, which includes natural and human disruptions,” Lu added. “Thousands of lines of algorithms are used behind the scenes to aid the computer model in making predictions. To reduce modelling uncertainties and include greater ecological process understanding arising from field scientists’ hard work, it will require decades of effort, and more to come.”