The nitrogen contained in agricultural fertilizers has helped crops grow faster to maximize yields and feed a growing number of people around the world. But nevertheless, this ally of mass food is also an enemy against climate change. The environmental impact of the use of this element in the agricultural world has been studied for years, but what was not known until now is that is negatively impacting one of the best carbon sinks: the soil.
A recent study, which has analyzed several corn farms, has found that nitrogen is causing carbon dioxide to return to the atmosphere instead of being sequestered in the ground, as occurs thanks to the decomposition of waste. The organic carbon that is formed makes it possible to preserve the health of the soil, improving its structure, its capacity to retain water and nutrients.
However, despite the fact that farmers have been feeding their soils with waste for decades, carbon, instead of increasing or staying the same, is decreasing. “Although thanks to intensive fertilization with nitrogen, it is possible to obtain more biomass and yield in the plantation -which means, in turn, that residues are deposited in the soil-, carbon is not maintained&rdquor ;, explains Richard Mulvaney, from the University of Illinois and one of the principal investigators of this study published in the open access scientific journal, MDPI.
And it is that these residues, therefore, have a component that does not allow them to fix carbon contributions as they should, and, according to this study, it is nitrogen that is behind this malfunction.
Not visible in the short term
The team studied how maize residues grown with and without fertilization impacted the soil. with nitrogen. “We designed an aerobic incubation study, adding these two residues to a culture soil with and without nitrogen,” explains Tanjila Jesmin, PhD researcher at NRES and co-signer of the article. The researchers then observed the decomposition process taking careful notes. of the production of carbon dioxide that it generated, while measuring the enzymatic activities and the microbial biomass that inhabited the soil.
They realized that nitrogen damage is not visible in the short term, which can be misleading about your benefits. As these researchers describe, initially adding nitrogen allows more carbon to be more present in the soil.
“It’s like burning leaves in the fall. The more leaves you put on the fire, the more flames you get. But when all the easily decomposable substrate has been burned, then that’s when the fire goes out,” Mulvaney says.
However, as time passes, the microbes that grow in that environment start to get hungrier than usual and use up all the carbon in their path. Thus, the soil goes from being an ally against climate change to a true enemy, since nitrogen allows all that carbon to be expelled back into the atmosphere.
Other Impacts of Nitrates
Apart from this new discovery, for years the scientific community has warned of the impacts that the use of nitrogen can have on ecosystems and specifically, on water, soil and air. In this sense, the contamination of water by fertilizers is produced mainly by leaching in groundwater and surface water.
The leaching of nitrates -product of some agricultural practices- facilitates its infiltration into subsoil and surface waters. This may imply that humans consume an excessive volume of nitrates, which could lead to health problems. Water with high concentrations of nitrates represents a health risk, especially in newborns. It can cause the “blue baby syndrome & rdquor; or methemoglobinemia, which inhibits the transport of oxygen in the blood, and can even cause death.
The negative impacts of fertilizers on the soil are the variation of pH, deterioration of the soil structure and microfauna. Finally, the negative impact on the air is mainly due to inadequate applications, which generates pollution in the environment.
And it is that the application of nitrogenous fertilizers can increase the emission of nitrous oxide (N20). Nitrous oxide is a greenhouse gas (GHG) that has about 300 times the warming effect of carbon dioxide. It is the main GHG emitted by the agricultural sector, surpassing the methane that derives from the digestive process of ruminants.
Nitrous oxide is produced by soil microorganisms, during a process known as denitrification, whose input is nitrates. The magnitude of this process increases in soils with high availability of nitrates and a lot of water.
To try to avoid these problems, the European Union promotes a circular economy based on the reuse and enhancement of by-products. Thus, alternatives to inorganic nitrogenous fertilizers based on organic sources are sought., such as the use of manure, slurry and waste from biogas plants.
But the problems caused by both types are similar. For this reason, in recent years, the debate has been oriented towards the need to adjust the fertilizer doses and apply only what is necessary based on the expected production. In this way, damage to the environment is minimized while the farmer’s costs are reduced. All this, preventing production from being reduced due to lack of nitrogen.
Reference study: www.sciencedaily.com/releases/2021/12/211215142207.htm. https://theconversation.com/nitrogen-fertilizers-as-essential-as-pollutants-122594