1052. Carbon Storage in Agriculture

Food production is responsible for one-quarter of greenhouse gas emissions in terms of carbon dioxide equivalent. Intensive farming practices aimed at feeding the world's population have allegedly led to carbon loss in the soil. However, in recent years, there have been high expectations for carbon storage in the agricultural sector as part of climate change mitigation measures.

On June 19, an op-ed in the journal Nature highlighted the efforts of farmers and scientists to develop farming practices that promote carbon sequestration while improving yields. 　

Agricultural technologies that promote carbon sequestration in the soil are not necessarily complex, but they need to be efficient, economically affordable, and rapidly adopted, particularly to achieve net-zero emissions globally through climate change mitigation and improved soil health, especially by 2050.

Soil organic carbon is is the carbon stored in the soil that is absorbed by plants from the atmosphere through photosynthesis and stored in the rhizome (root) system, among other things.

Increasing soil carbon is not technically challenging, but humanity's desire to pursue short-term returns from soil has prevented it from becoming a reality. In particular, deep tillage accelerates the decomposition of organic matter, and the supply of nutrients to crops has led to increased harvests. This process has led to carbon dioxide emissions from the soil into the atmosphere, destroying the soil structure and increasing the risk of soil degradation due to water and wind erosion, leading to a vicious cycle of further greenhouse gas emissions.

As one of the methods for storing carbon in the soil, attention has focused on the potential of no-till and minimal tillage, which leave soil organic matter as it is without disturbing the soil structure. However, it's important to note that evidence does not support the idea that no-till necessarily increases soil carbon storage; rather, the amount of stored soil carbon seems to depend on climate and soil type.

Another way to retain soil carbon is through the introduction of cover crops, which seem to be becoming more prevalent in vineyards in North America and Europe. In addition, there has recently been a growing interest in carbon sequestration through the introduction of basalt into the soil and the weathering of rocks. On the other hand, although deforestation remains the main source of carbon emissions from agriculture,  agroforestry in agricultural systems is also attracting attention.

Dr. Rattan Lal of Ohio State University, a renowned soil researcher, estimates that if the world were to switch to non-fossil fuels, soil carbon sequestration from agriculture would exceed emissions in the long term.

On the other hand, the soil science community is also divided on the potential of soil carbon storage, citing the difficulty of measuring soil carbon content as the cause. Since the amount of soil carbon fluctuates even over a small spatial distance, it requires a lot of people to measure accurately, and it also fluctuates depending on natural conditions and time factors, so it is inevitably costly to measure.

It has also been pointed out that farmers do not always accept the opinions of scientists, and that they need to overcome socio-cultural barriers. Interestingly, farmers already engaged in carbon farming seem to recognize the effects of climate change beyond mere economic benefits from carbon credits and are driven by the need to restore the environment.

Reference
How farming could become the ultimate climate-change tool: A generation of farmers and scientists are finding ways to sequester carbon in the soil while improving crop yields. By Bianca Nogrady. Nature 630, S23-S25 (2024) https://www.nature.com/articles/d41586-024-02036-x

Contributor: IIYAMA Miyuki, Information Program