Mr. Peanut and the “Forgotten” Greenhouse Gas

I went looking for inspiration for my first MScCCAFS research project blog post. I found an article in the BBC’s Future Planet series titled The World’s Forgotten Greenhouse Gas. It explored some of the emerging technological strategies to mitigate nitrous oxide (N2O) emissions from agricultural production. Ironically though, in an article about a forgotten greenhouse gas, it also highlighted a forgotten mitigation strategy – Legumes. A major player in agriculture and the topic of my research project. By including their benefits in the narrative, I was able to better understand my own research objective.

“Humanity has tipped the Earth’s nitrogen cycle out of balance.”

As the article highlights, N2O molecules are both long lived and about 300 times as potent as CO2. Yet in the carbon-centric political mindscape, as a dangerous greenhouse gas, nitrous oxide is often invisible, overlooked and forgotten. All the while it is expelled in vast quantities from agricultural production, wreaking havoc with the Earth’s nitrogen cycle and contributing significantly to climate change.

“Synthetic nitrogen fertiliser is the culprit”

Nitrogen (N) is the limiting element in agriculture and with population growth, farmers have had to turn to synthetic fertiliser to boost crop yields. Between 1960 and 2000, global agricultural productivity increased substantially because of the use of fertilisers 1. However, the numbers reveal that over time this strategy gives diminishing returns and is now beyond the point of profitability or sustainability 1. Currently, for every 100 kg of N applied to the soil, about 1 kg is lost to the atmosphere as N2O 2. In addition, the fossil fuels used for the chemical synthesis of nitrogen fertilisers contribute 10% of agricultural emissions and 1% of all anthropogenic greenhouse gas emissions 1.

“Can we cut emissions from its greatest source?”

The technological innovations to improve efficiency include remote sensing technology to determine when, where and how much fertiliser to add to land, and harnessing beneficial soil microbes to directly supply biological nitrogen to crops through fixation of atmospheric nitrogen. Legumes however, beating us to the punch by only a few thousand millennia, have already harnessed these microbes within their root system and sustainably generate their own reactive nitrogen (Nr). Consequentially they occupy a critical niche in agriculture. Forage peanut cultivars for example, of the genus Arachis, when mixed with grasses, provide a low-cost supply of Nr not only for themselves but for the crops around them 3. This reduces the need for synthetic fertilizers, lowering waste in the form of N2O 3. In addition, the extra Nr now available in the soil contributes to improved health across the board and reduces the need for tillage, further decreasing soil based greenhouse gas emissions 2.

Credit: Getty Images

Why then do legumes not feature in the BBC’s Future Planet story…..?

In a future themed article, perhaps they didn’t fit the technological angle. Legumes are not a new discovery. They appear as “A thread of archeological and written record since the emergence of evidence for the management of plants and animals for food” 4 . But their omission is perhaps more indicative of how far they now lag behind the major cereal crops in terms of management, breeding strategies and indeed technology 5.

With a few exceptions, they have failed to deliver improvements in agricultural productivity, particularly in the tropics 3. Unsuccessful experiences in establishing and maintaining productive and persistent grass-legumes mixtures generated a lack of credibility among farmers and researchers 3. They have also been pitched against the increasing availability of cheap fossil fuels for the chemical synthesis of fertiliser, until now masking a lack of action on sustainable alternatives 2, 6 . As a result, they remain a largely misunderstood and underutilised resource in Climate Smart Agriculture.

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In response, The United Nation’s Sustainable Development Goals now seek a greater contribution of legumes to Food Security and Climate Action targets 5 . And progress is being made. Those same forage peanuts for example are now being successfully adopted in Nepal, Australia, Brazil, Colombia and the southern United States 3. The challenge lies in ensuring knowledge gains, policy developments and technological innovations continue on equal footing with cereal crops. Exploring new breeding technologies is, in a (pea)nutshell, the objective of my research project. It is my intention over the coming weeks, as I progress through the literature, to provide further insight into what some of these technologies are and how we can utilize them in the best possible way.

In the fight against climate change, the personal story of Mr. Peanut has only just begun…

1. Scialabba, Nadia El-Hage, and Maria Müller-Lindenlauf. 2010. ‘Organic agriculture and climate change’, Renewable Agriculture and Food Systems, 25: 158-69.

2. Jensen, Erik Steen, Georg Carlsson, and Henrik Hauggaard-Nielsen. 2020. ‘Intercropping of grain legumes and cereals improves the use of soil N resources and reduces the requirement for synthetic fertilizer N: A global-scale analysis’, Agronomy for Sustainable Development, 40: 1-9.

3. Valentim, Judson Ferreira, and Carlos Mauricio Soares de Andrade. 2020. “Strategies leading to successful wide adoption of mixed grass-legume pastures for sustainable intensification of beef cattle production systems in the Brazilian Amazon.” In Embrapa Acre-Artigo em anais de congresso (ALICE). In: INTERNATIONAL SYMPOSIUM ON AGRICULTURAL TECHNOLOGY ADOPTION, 1., 2019 ….

4. Delwiche, CC. 1978. ‘Legumes—past, present, and future’, Bioscience, 28: 565-70.

5. Varshney, Rajeev K, Manish K Pandey, Abhishek Bohra, Vikas K Singh, Mahendar Thudi, and Rachit K Saxena. 2019. ‘Toward the sequence-based breeding in legumes in the post-genome sequencing era’, Theoretical and Applied Genetics, 132: 797-816.

6. Foley, Jonathan A, Navin Ramankutty, Kate A Brauman, Emily S Cassidy, James S Gerber, Matt Johnston, Nathaniel D Mueller, Christine O’Connell, Deepak K Ray, and Paul C West. 2011. ‘Solutions for a cultivated planet’, Nature, 478: 337-42.