Computer models show how crop production increases soil nitrous oxide emissions

Date:
February 15, 2022
Source:
Iowa State University
Summary:
A computer modeling study shows how the emissions of the
greenhouse gas nitrous oxide have increased from soils over the
last century. The newly published research found the expansion of
land devoted to agriculture since 1900 and intensive fertilizer
inputs have predominantly driven an overall increase in nitrous
oxide emissions from U.S. soils.



FULL STORY ==========================================================================
A recent ecosystem modeling study conducted by Iowa State University
scientists shows how crop production in the United States has led to
an increase in the emissions of nitrous oxide, a potent greenhouse gas, throughout the last century.


==========================================================================
The researchers drew on massive amounts of data on everything from weather patterns to soil conditions to land use and agricultural management
practices in order to feed the model and quantify changes in nitrous oxide emissions from soils in the United States. The research, published in the peer-reviewed academic journal Global Change Biology, break soil emissions
down by ecosystem types and major crops and found that the expansion of
land devoted to agriculture since 1900 and intensive fertilizer inputs
have predominantly driven an overall increase in nitrous oxide emissions.

The use of such ecosystem models to assess the sources of nitrous oxide emissions could help guide policymakers as they enact conservation plans
and responses to climate change, said Chaoqun Lu, associate professor
of ecology, evolution and organismal biology and corresponding author
of the study.

"The model we are using is a process-based ecosystem model," Lu
said. "It's similar to mimicking the patterns and processes of an
ecosystem in our computer. We divide land into thousands of pixels at a
uniform size and run algorithms that simulate how ecological processes
respond to changes in climate, air composition and human activities."
Results show emissions tripled The study found nitrous oxide emissions
from U.S. soil has more than tripled since 1900, from 133 million metric
tons of carbon dioxide equivalent (MMT CO2 eq) per year at the beginning
of the 20th century to 404 MMT CO2 eq per year in the 2010s. Nearly three-quarters of that rise in emissions originates from agricultural
soils with corn and soybean production driving over 90% of the ag-
related emissions increase, according to the study.

"Our study suggests a large [nitrous oxide] mitigation potential in
cropland and the importance of exploring crop-specific mitigation
strategies and prioritizing management alternatives for targeted crop
types," the study authors wrote in their paper.

The rise in emissions corresponds to an expansion of cropland in
the United States, Lu said. The computer models found land devoted
to agricultural production emits more nitrous oxide than natural
landscapes. That's largely due to the widespread application of nitrogen fertilizers to agricultural land and legume crop production, Lu said. The
added nitrogen is partially used by crops, and the remainder either
stays in soils or is lost to the environment. During this process, microorganisms living in soils consume nitrogen-containing compounds
and give off nitrous oxide as a byproduct. Better understanding the
dynamics of which crops lead to the greatest emissions can help shape
climate mitigation policy, Lu said. Because more nitrogen fertilizer is
applied in corn production on average than other crops, the study found
soils where corn is grown tend to emit more nitrous oxide per unit of fertilizer used, Lu said.

The researchers designed mathematical models that mimic ecological
processes.

The models rely on mountains of data gathered and developed over the
course of years, Lu said. The researchers compiled government data on
crops, land use, weather and other variables. They also factored in
historic and survey data from farmers and other landowners.

The research team also compared the results from their model with
real-world data in order to validate their results. For instance, the scientists showed their model's yield predictions tracked with national
yield records dating back to 1925 for major crops such as corn, soybean,
wheat, rice and others. That shows the model simulation could track the long-term trajectory of nitrogen uptake that supports increasing crop
yield over the past century. They also compared their model's nitrous
oxide emission predictions to real-world data collected from multiple
natural and managed soils across the nation, as well as time-series measurements from a central Iowa corn-soybean rotation site over the
course of seven years.

"Our group has spent lots of time improving model performance and
developing the driving force history, including natural and human
disturbances, for the model simulations," Lu said. "Behind the scenes,
there are thousands of lines of algorithms to guide the computer model
to make predictions. It takes decades of efforts, and more to come,
to reduce modeling uncertainties and incorporate better ecological
process understanding resulting from the hard work of field scientists." ========================================================================== Story Source: Materials provided by Iowa_State_University. Note: Content
may be edited for style and length.


========================================================================== Journal Reference:
1. Chaoqun Lu, Zhen Yu, Jien Zhang, Peiyu Cao, Hanqin Tian, Cynthia
Nevison.

Century‐long changes and drivers of soil nitrous oxide (N
2 O) emissions across the contiguous United States. Global Change
Biology, 2022; DOI: 10.1111/gcb.16061 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/02/220215125505.htm

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