In early January 2025, the World Meteorological Organization (WMO) announced that 2024 was the warmest year on record, with average temperatures soaring 1.55 degrees Celsius above pre-industrial levels. This new high surpassed the previous record from 2023, which saw an increase of 1.45 degrees Celsius.
The annual Climate Change Conferences of the Parties (COPs) continue to unite stakeholders worldwide to tackle the climate crisis. During COP29, after years of negotiations, parties reached a historic agreement on Article 6 of the Paris Agreement, focusing on carbon markets and allowing emissions trading to bolster mitigation efforts and curtail temperature rises.
Carbon credit trading aims to enhance sequestering and capturing techniques of carbon, the most prevalent greenhouse gas driving global temperature increases. Emission reduction projects, in this context, strive to sequester or isolate carbon through various innovative methods. Of particular interest are areas that can absorb substantial amounts of carbon, with soil recognized as a vital carbon sink. Consequently, scientists have intensely studied soil, yielding valuable insights and data to combat climate change.
Hypothesis
Diverse cropping systems, where multiple crop types are cultivated alongside livestock in a single field, have garnered considerable support recently. This method is believed to enhance carbon input and storage in the soil, leading to the hypothesis that diverse cropping systems mitigate the adverse environmental impacts of conventional agriculture. Researchers set out to test this hypothesis.
A research team from the University of Iowa, the United States, conducted a study to explore the benefits of diverse cropping systems in greater depth. Their findings were published in the Nature Sustainability on January 2, 2025. The study revealed that while agricultural rotations involving various crops provide numerous environmental benefits, they are less effective at sequestering carbon than previously assumed.
Research Study
The researchers analyzed field data and soil samples from an Iowa farm, spanning back to 2001. Their study encompassed two-year corn-soybean rotations, three- and four-year alfalfa-oat rotations, and systems using cattle manure as fertilizer instead of synthetic nitrogen. Carbon isotope analysis was utilized to determine the duration of carbon retention in the soil.
Key Findings
The study found that increased crop diversity in three- and four-year rotations boosted carbon inputs, resulting in higher organic matter levels. This, in turn, stimulated microbial activity, leading to increased decomposition and elevated carbon dioxide emissions.
Moreover, the conversion of organic nitrogen to inorganic nitrogen in the soil samples enhanced nitrogen availability in diversified cropping systems, reducing the need for synthetic fertilizers and subsequently lowering nitrous oxide emissions.
The researchers concluded that while diversified cropping systems contribute organic fertilizers to the soil, they do not effectively sequester carbon. These insights are crucial for decision-makers and those involved in carbon markets, as they provide a clearer understanding of the soil's capacity to sequester and retain carbon under various land-use practices.
