Human action alters the balance of nitrogen and phosphorus, essential elements for life

The magazine Science today publishes an article from the perspective of researchers at the Center for Ecological Research and Forest Applications, Josep Penuelas and Jordi Sardans regarding the imbalance of nutrients in the soil, its effects on life and possible solutions. The writing is based on data from recent studies by both experts and presents the state of the issue and its scope to the international scientific community. Furthermore, propose alternatives and solutions aimed at people with political decision-making power.

According to Peñuelas and Sardans, ecosystems and species are at risk due to global nutrient imbalance that we humans are causing and that alters the proportion of nitrogen and phosphorus in land and water, two essential elements for life. Both nitrogen and phosphorus affect the growth rate of microorganisms, plants and animals.

Plant species need CO_two to carry out photosynthesis and nutrients to create their structures, among which the proportion of nitrogen and phosphorus is fundamental. In addition, for optimal growth, adequate amounts and proportions of nitrogen and phosphorus are required. However, in recent decades, humans we enrich the biosphere with nitrogen through over-fertilization and, therefore, we have modified its relation to phosphorus.

“The time has come for national and international environmental agencies and politically responsible individuals to recognize the risks they pose to the biosphere and humanity imbalance between nitrogen and phosphorus. International environmental organizations must address the problem through a coordinated international policy”, according to researcher Josep Peñuelas, CSIC research professor at CREAF.

Alternatives to imbalance

Among the possible alternatives, experts recommend increasing efficiency in the use and cycle of nitrogen and phosphorus thanks to the precision agriculture, which avoids disproportionate application of fertilizers. They also advocate the application of methods, both management and innovative biotechnology, which increase plant efficiency by capturing nutrients and benefiting from phosphorus sources. Other necessary policies pointed out by Peñuelas and Sardans are stimulate phosphorus recycling through national and regional regulations, subsidies or laws, as well as reduce livestock production. These types of solutions are in the initial phase of application.

Humans are over-fertilizing the biosphere with nitrogen through nitrogen oxides emitted by burning fossil fuels. Planting nitrogen-fixing crops and using enriched fertilizers that also seep into waterways. Although there are also human activities that have increased the amount of phosphorus in soils and water – for example, the application of fertilizers and detergents rich in this element –, the global increase in the presence of phosphorus in the soil is still smaller than that of nitrogen.

In fact, they are two synergistic problems. On the one hand, the presence of nutrients in the soil increased disproportionately and, on the other hand, the balance between nitrogen and phosphorus was altered. When the medium contains too many nutrients, it becomes eutrophic: the increase in nutritive substances in fresh water causes algae and phytoplankton to grow uncontrollably, until the ecosystem collapses. Therefore, some countries have promoted water treatment strategies aiming to reduce the concentration of both chemical compounds. However, the technology used by water treatment plants retains more phosphorus than nitrogen, further promoting an imbalance between the two nutrients.

A question of stability

The global imbalance between nitrogen and phosphorus could be even greater at local and regional level, since the contributions of both compounds are not evenly distributed across the world. Furthermore, as they have a very different capacity to affect the environment: phosphorus, for example, is less soluble in water and does not volatilize, it is often adsorbed and precipitates in the soil in the mineral form, remaining buried in the sediments. Therefore, it tends to stay close to its emission source. In contrast, nitrogen is much more soluble in water and much more volatile, which facilitates its dispersion over a greater radius of its emission source.

THE biological impacts of the growing imbalance between the two nutrients have been observed in inland water bodies, in the structure and function of communities of living beings in the soil, as well as in the species composition of plant communities. The lack of stability will have an increasing impact as the imbalance continues to tilt in the same direction.

human phosphorus crisis

THE food security and the Agricultural production They are the most affected by this imbalance, which directly impacts natural ecosystems and people. Nitrogen-containing fertilizers have an unlimited source – the atmosphere – from which this nutrient can be extracted via the Haber-Bösh reaction. This innovation has allowed its production to increase continuously, as well as its use as a fertilizer since the 1950s. However, phosphorus sources have been largely limited to mines and are concentrated in very few countries, as is the case in Morocco.

In this sense, Phosphorus may become economically inaccessible for low-income, food-deficit countries, as these sources become depleted or geopolitically and economically unavailable. In the future, phosphorus-producing countries are likely to manage their reserves to maximize the profits of their national mining and agriculture industries, making phosphorus-based fertilizers increasingly inaccessible to farmers in poorer countries and further exacerbating the imbalance between the two nutrients in the regions where the problem is more pronounced. It would be a crisis that would further aggravate the economic gap between rich and poor countries.

Phosphorus and sick nitrogen

The lack of balance between these two elements in the soil modifies the chemical composition of the crops and can affect the health of the people who consume the products grown on these lands and, therefore, a public health problem. For example, in regions where there is excessive use of inorganic and organic phosphate fertilizers, phosphorus accumulates in soils and water bodies.

Food produced in these environments can cause the local population to over-consume phosphorus, which can have negative implications for their health. Nutritional imbalance is also known to affect infectious and non-infectious human diseases that are strongly associated with diet, such as celiac disease. CREAF researchers already warned in 2021 that the excessive fertilization of wheat crops with nitrogen could explain the high prevalence of celiac disease.

Finally, CREAF researchers point out that when the relationship between nitrogen and phosphorus is destabilized, human activities also generate imbalances between other elements. For example, changes in the ratio of carbon to nitrogen in relation to iron, zinc, calcium and potassium, among others, have been observed in plant tissues.