Accumulation of carbon dioxide in the atmosphere and impoverishment of farmland

The high concentration of carbon dioxide (CO2) in the atmosphere has negative effects on food security that go beyond the merely climatic.

According to the conclusions of a recent study, a high concentration of CO2 in the atmosphere reduces the availability of phosphorus in soils where rice is grown by more than 20%. This fertilizing mineral is indispensable for a productive soil.

The study was carried out by an international team of specialists from Australia, Spain, Canada, the United States, France and China, including experts from the Center for Ecological Research and Forestry Applications (CREAF) at the Autonomous University of Barcelona (UAB), and from the Council Superior of Scientific Investigations (CSIC), in Spain.

The study has been based on two long-term experiments in which rice fields have been studied under conditions of high carbon dioxide.

The results of the study predict a great risk of reduced rice yields, especially in low-income countries, a situation that places them in adverse conditions and further widens economic inequality due to CO2 emissions and impacts on processes. geochemicals. The conclusions show that 55% of large paddy fields in China and India will experience increased risk of yield reduction due to phosphorus deficiency. In relative terms, low-income countries (apart from China and India, especially those located in Southeast Asia, Central America, South America, Africa and the Middle East) will experience more critical situations, as 70% of rice paddies are expected to suffer greater risks of reduced performance, compared to 52% in high- and middle-income countries.

The work has revealed a contradiction: although atmospheric CO2 is the main source of carbon for crops, its high concentration in the atmosphere limits the presence of phosphorus fertilizer in the soil in the long term. This mineral is essential for the metabolism and growth of plants in agricultural soils. As explained by CREAF and CSIC researcher Josep Peñuelas, “when there is a high concentration of CO2 in the atmosphere, plants enjoy this fertilizing effect in the short term, but in the long term, in rice crops they no longer have available phosphorus and the Soil becomes impoverished, so plant growth is compromised.

As a consequence, this compromises food security in a context of world population growth where rice plays a key role.

A rice paddy. (Photo: USGS)

A global challenge

Phosphorus chemical fertilizer is unevenly distributed around the world and is made from rock phosphate, a non-renewable resource. 70% of its reserves are in Morocco and Western Sahara and many countries depend on imports to dispose of them. Therefore, its sustained deficit can cause a limited agricultural yield to certain regions of the world. In addition, this situation may worsen in the future given the continuous increase in atmospheric CO2 levels, which limit the presence of phosphorus.

The situation poses an international sociopolitical challenge, due to access to this mineral with fertilizing capacity. “The difficulty of countries with less purchasing power to fertilize their farmlands with phosphorus supplements is evident and worrying,” says Peñuelas. In fact, during the world food crisis of 2007-2008, the price of phosphate rock and fertilizers increased by 400% in 14 months, indicative of the strong socioeconomic instability associated with phosphorus. This price increase has also occurred in 2022.

As an alternative, the scientific team argues that it is urgent to plan international phosphorus management strategies that take into account future global changes.

Compensate, a questioned alternative

Fertilizing agricultural soils seems to be the ideal alternative to offset phosphorus reductions caused by atmospheric carbon dioxide in the long term, but it has consequences that must be avoided. On the one hand, the excessive fertilization of arable soil with phosphorus to maximize production accumulates this mineral in countries with high purchasing power that can afford it, basically in Europe, North America and some in Southeast Asia. And, on the other hand, the phosphorus accumulated in the soil is lost through rainwater runoff, erosion and leaching (the loss of water-soluble nutrients). In addition, the excessive presence of this mineral in river and marine waters is the main cause of the appearance of harmful algae, the death of fish in estuaries and coastal waters, and the generation of dead zones, a situation known to science as eutrophication.

For the first time, the two scientific experiments have been carried out in periods of 15 and 9 years with rice. FACE (Free Air CO2 Enrichment) technology, the most widely used by science, has been applied to raise the concentration of atmospheric carbon dioxide and examine the responses of the biosphere. FACE is neither cheap nor easy to maintain, which is why experiments that apply it over a decade are rare and highly unique around the world.

The study is titled “Reduced phosphorus availability in paddy soils under atmospheric CO2 enrichment”. And it has been published in the academic journal Nature Geoscience. (Source: CSIC / CREAF)