When it comes to fertilizers, it is important to balance: if the right amount is used in a timely manner, yields will increase, helping to feed a growing world population, but excessive use is harmful to plants, polluting soil and water and exacerbating global warming.

How can we find the right balance? Isotopic techniques can be used to optimize fertilizer use, assess the impact of agrochemical pollutants and identify sources of greenhouse gas emissions, among other things.

Helping farmers and reducing greenhouse gas emissions

“The world’s population is more numerous than ever before, but the problem of food cannot be solved by simply increasing the dose of fertilizer.

Excessive use of fertilizers is the main reason why agriculture has become a major source of greenhouse gases over the past 70 years,” said Christoph Mueller, a botanist and soil scientist at the Institute of Plant Ecology at Gisen University in Gisenburg.

He also said that he would like to hear from Mr. Eustus Liebich (Germany) and the School of Biology and Ecology at University College Dublin. According to the Food and Agriculture Organization of the United Nations (FAO), agriculture, including forestry and other land-use options, accounted for 24 per cent of global greenhouse gas emissions in 2014.

We need to protect the environment while at the same time helping farmers, but we need to be clear about how fertilizers affect the soil and crops, and under what conditions greenhouse gas emissions begin,” Müller says.

Nuclear techniques can help us answer these questions and develop effective ways to increase crop yields and reduce our environmental impact.

Plants and soil convert fertilizers into nutrients and produce by-products, including greenhouse gases such as carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4).

If the right amount of fertilizer is used, plants develop well and greenhouse gas emissions are minimized. However, if fertilisers are overused, plants cannot process them – the excess remains in the soil, causing a sharp increase in emissions.

Muller, together with a team of scientists from nine countries and IAEA and FAO experts, is conducting an isotope tracking experiment to understand the relationship between fertilizers, crops, soil and greenhouse gas emissions (see Science box).

The same methods are used in the framework of the FACE experiment: in this way, scientists are studying how increasing CO2 levels in the atmosphere caused by climate change will affect crop quality and fertilizer requirements.

The results of isotope studies will be taken into account in the development of regulations that will reduce the amount of fertilizers used in agriculture without compromising crop quality and yields.

The results of the research have already helped to identify ways to optimize fertilizer use on more than 100 hectares of pastures and rice fields, maize and wheat. Greenhouse gas emissions decreased by 50% and yields increased by 10%.

“As part of the FACE experiment, we found that plants grow faster, but their quality is changing,” Müller said. FACE is a major project to study climate change in the wild.

At the Gisen test site in Germany, one of the longest experiments of its kind is being carried out. It consists of simulating the change in carbon dioxide levels in the atmosphere above a typical meadow, which is expected to occur by the middle of this century.

Plants grown at high CO2 levels are becoming tougher and their protein content is decreasing. Cows grazing on such meadows are more difficult to digest and have to consume more food to produce milk.

This not only jeopardizes milk production, but also leads cows to produce more methane, a greenhouse gas, 34 times more powerful than CO2.

Detection of fertilizers in drinking water and not only

Excessive use of fertilizers not only contributes to greenhouse gas emissions. Rainfall currents or meltwater often bring fertilizers into rivers and streams, from which they flow into oceans or drinking water reservoirs.

Pollutants used in agriculture can make water unsuitable for drinking and cause damage to aquatic ecosystems and biodiversity,” said Lee Heng, Chief of the Soil, Water and Plant Nutrition Section of the Joint FAO/IAEA Food and Agriculture Division. —

Nutrients in fertilizers stimulate algae growth, which reduces oxygen levels in the water, damaging fish and aquatic ecosystems.

Hen said fertilizers are among the agrochemicals that pollute the environment. This category also includes pesticides, salt from irrigation water, sediments and residues of medicines used in animal husbandry.
These substances are increasingly being used to increase productivity and minimize the impact of climate change.

Scientists from 15 countries work with experts from the Joint FAO/IAEA Division and, through the tracking of a set of stable isotopes, analyse pollutants in agriculture, identify their sources and patterns of movement (see box on Science).

These methods can be used to identify the sources of contaminants in agriculture and to develop innovative and effective practices to control overuse of fertilizers and reduce their environmental impact.

Scientists have been using separate isotopes for more than 20 years to identify contaminants in agriculture, but the use of a single isotope does not provide enough information at a time to identify different contaminants and their distinct isotopic signatures.

“The use of a set of isotopes allows scientists to better understand the sources of pollution, allowing them to decide which approach would be more effective in controlling contamination in the fields and in different landscapes.