F and A
  MAY 2019 


Scientist Xin Zhang on the Nitrogen Cycle, Climate Change & Nitrogen Use Efficiency

Much of your past research has focused on the nitrogen cycle. What drew you to the topic?

Nitrogen is the building block of life on earth and affects almost every aspect of our daily life. However, the excessive use of nitrogen in agricultural production has led to unintended impacts on the environment, including regional water and air pollution, as well as ozone depletion and greenhouse gas emissions. Too much or too little nitrogen will lead to significant socioeconomic and environmental problems. How to get the right amount of nitrogen to provide nutritional food for the world while minimizing the adverse environmental impacts is one of the major challenges for achieving the Sustainable Development Goals.

I am also interested in the nitrogen cycle because of its interdisciplinary nature. For example, the nitrogen cycle involved in agricultural production is determined by both biophysical processes, such as soil-plant nitrogen dynamics, and socioeconomic processes, such as farmers’ decision making and crop markets. While many research efforts have been devoted to understanding the biophysical dynamics of cropping systems, few have fully integrated socioeconomic processes due to the segregation of traditional disciplines. I am excited to be among those researchers who have been pioneering efforts to break down the boundaries of traditional disciplines and understand and manage nitrogen cycles as coupled by human and natural systems.

How do you see climate change affecting agricultural nitrous oxide emissions?

Climate change affects agricultural nitrous oxide (N2O) emissions in two different ways:

1) The changes in temperature and precipitation will affect the denitrification and nitrification processes in soil and consequently affect the emission rate of N2O, a by-product of those processes. For example, N2O emissions are likely to increase in the US Corn Belt as the climate gets warmer and wetter.

2) The increasing temperature and atmospheric CO2 concentrations may increase crop N uptake in some regions, reduce the amount of soil N available for the denitrification processes, and consequently reduce N2O emissions. On the other hand, if increasingly frequent floods and droughts result in decreased crop productivity or even crop failure, then more of the applied nitrogen is likely to be lost to the environment, including as N2O, when extreme weather events become more common as is expected under climate change scenarios. Climate change is likely to make nutrient management more challenging.

Overall, those impacts are location-specific and have not been well quantified yet.

What do you think can be done to make nitrogen fertilizer use more efficient?

More efficient nitrogen fertilizer use requires a systematic change, involving not only farmers and fertilizer companies, but also stakeholders along the food supply chain. While 4R nutrient management principles (i.e. “Right” time, type, place, and amount) are critical for improving nitrogen use efficiency (NUE) on a plot or farm scale, I would like to argue that “right” price and policy are also necessary to enable and incentivize farmers to implement those nitrogen-efficient technologies and management practices and to improve the efficiency on broader spatial scales.

Given the complex trade-offs and responses of markets, governments, and consumers, technologies and practices (such as enhanced efficiency fertilizers and improved crop breeds) that have proven to be efficient at a plant or plot scale do not necessarily lead to the reduction of agricultural nitrogen use on a regional to national scale. For example, changes in trade relationships may lead to shifts in crop production and consequently affect regional nitrogen use. Research on such complex dynamics involving both socioeconomic and ecological processes is necessary for assisting policy-making on a regional scale. Research and Development efforts on new fertilizer products and crop varieties should be informed, or even guided, by their potential impacts on the regional scale.

The choices made by stakeholders, such as consumers and retailers, will affect farmers’ decisions about what and how to plant, and consequently influence the efficiency of fertilizer use. Many indicators have been developed to inform those choices, including the Nitrogen footprint of food products and “nitrogen balance” of crop products. While more research efforts are needed to improve the methodology and data quality of those indicators, stakeholders, including industry and NGOs, can already use them to encourage more efficient nitrogen use through product labeling and requirements placed upon suppliers.

Can you tell us about some of your current and upcoming research?

The major goal of my work is to evaluate how socioeconomic and biogeochemical processes affect the global nutrient cycle and the sustainability of agricultural production and, in turn, provide policy input on mitigating nutrient pollution while meeting global food and biofuel demands. I am currently leading several exciting research projects on nutrient management and sustainable agriculture:

1) Sustainable Agriculture in the nexus of food, energy, water, and nutrients on national and global scales: Funded by the National Science Foundation, this project will assist decision-making on a national scale and help to visualize the global implications of agricultural intensification strategies. We have been rigorously testing the impact of trade on agriculture sustainability in China and U.S. and improving the representation of crop management in the Global Change Assessment Model to project the impacts of agricultural intensification.

2) Sustainable Agriculture Matrix (SAM): With support from the National Socio-Environmental Synthesis Center and NSF, I have been coordinating a highly interdisciplinary team of experts to develop a Sustainable Agriculture Matrix, a collection of indicators measuring sustainable agriculture from the environmental, social, and economic dimensions on a national scale to help guide evolving policies.

3) Sustainable nitrogen and phosphorus management in crop production: Following my publication on sustainable nitrogen management, we have developed a database of P budget and P use efficiency (PUE) by region and crop type, identified and tested a group of socioeconomic and ecological drivers critical for PUE improvement, projected P fertilizer consumption up to 2050 under various policy and technology scenarios, and identified policy and technology implications for addressing the triple challenges of food security, P supply, and the environment. This research effort is supported by OCP Research LLC.

4) Tracking fast-evolving national nitrogen budgets in crop production: A voluntary effort by about ten major research groups on nitrogen cycles to compare the existing nitrogen (N) budget estimates from various approaches and spatial scales and assess their uncertainties in a systematic manner. This first-of-its-kind comparison on crop N budgets has revealed major gaps in our understanding of N budgets, including the lack of high-quality data in crop N content and detailed location- and crop-specific fertilization data.

About Xin Zhang

Xin Zhang is an Assistant Professor at the University of Maryland Center for Environmental Science (UMCES). Xin’s research approaches are from both natural science, including the Earth System Model and atmospheric measurements, and social science, such as econometrics analysis.

Collaborating closely with economists, modelers, and field experimentalists worldwide, Xin has published papers on various peer-reviewed journals, including Nature and Proceedings of the National Academy of Sciences, and has received research grants from multiple institutions, including National Science Foundation and OCP Research LLC.

Xin received a Ph.D. from Yale University (2013) and did postdoctoral research at Princeton University before joining UMCES. In addition to her academic education, she has completed internships and projects at various national and international organizations, including the United Nations.


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