CM – Keeping more ammonium in the soil can reduce pollution and boost crops

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May 27, 2021

from Princeton University

Modern agriculture faces two major dilemmas: how can you produce enough food to feed the growing human population, and how can you minimize the environmental damage associated with intensive farming? Keeping more nitrogen than ammonium in the soil can be key to addressing both challenges, according to a new article in the Proceedings of the National Academy of Sciences (PNAS).

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Today’s use of nitrogen fertilizers is a major contributor to greenhouse gas emissions, air pollution, and water pollution, but is also essential for growing crops. Reducing this pollution is critical, but nitrogen use is likely to increase as food production increases. At the same time, the world’s population is growing, and agriculture must efficiently produce enough food to feed everyone without clearing more forests for agriculture.

In the past, farmers have succeeded in increasing food production by reducing their agricultural needs Add more nitrogen fertilizer to areas. However, this is no longer a workable or acceptable solution. Instead, farmers should consider switching to a mixture of nitrate and ammonium, which can reduce pollution and increase food production. Ammonium, a form of nitrogen, binds to the soil and is therefore less likely to end up in waterways.

« Current fertilizer systems are polluting, inefficient and detrimental to ecosystem health, » said the paper’s co-author, Guntur Subbarao, a senior researcher at the Japan International Research Center for Agricultural Sciences (JIRCAS). « If agriculture can shift from using full nitrate in soils to a nitrate-ammonium mixture, it could have far-reaching implications for limiting nitrogen pollution while increasing crop yields. »

« New tools conserving more soil nitrogen in the form of ammonium could also enable the selection of plant varieties that produce higher yields by mixing nitrogen forms, « said co-author Tim Searchinger, a senior scientist at the Center for Policy Research on energy and the environment at Princeton University’s School of Public and International Affairs. « There is a prospect of dual benefits in reducing nitrogen pollution, including greenhouse gas emissions, and helping the world save forests by producing significantly more food on the same land. » Most nitrogen pollution reduction strategies are based on limiting « front end » pollution by trying to apply fertilizer more carefully. However, the authors state that no matter how carefully fertilizer is applied, nitrogen always comes out at the « rear end ». This leakage occurs because soil nitrogen is quickly converted to nitrate in farmland, a form of nitrogen that leaches easily in groundwater and waterways and which, when broken down, releases nitrous oxide, a powerful greenhouse gas.

This is where ammonium comes in, they say Authors. It will not break down into laughing gas unless it is first converted to nitrate. The article shows that while high levels of ammonium are toxic to most plants, an underappreciated line of research has shown that a mixture of nitrate and ammonium tends to significantly increase crop yields by as much as 50% or more compared to typical soil conditions now almost all of them are nitrates.

This academic finding was irrelevant until recently, as microorganisms in cultivated fields quickly convert nitrogen to nitrate in a process known as nitrification. However, the authors identify two new ways to maintain a better balance of nitrogen forms in soils. One is to use synthetic nitrification inhibitors with coatings to limit nitrification for extended periods of time. The other is to take advantage of some plants’ natural ability to prevent nitrification. A plant trait that prevents microbes from converting ammonium to nitrate was first discovered in a commonly planted tropical grass. However, researchers have recently started breeding varieties of all the major grains like wheat to preserve this trait.

By growing plants that could benefit from ammonium and aid ammonium retention in the soil by inhibiting nitrification Farmers, scientists and policy makers effectively increase food production while minimizing environmental degradation. The authors recommend additional research efforts as there is currently no large-scale financial support for this effort. They also recommend guidelines shifting fertilizer subsidies to fertilizer forms or plant varieties that inhibit nitrification.

« A major benefit of this research is that once these varieties are made, all farmers around the world should be able to do so to use them at no additional cost and with the benefit of higher yields, « Subbarao said.

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