Column - On the Subject

What the atomic bomb can teach us about the future of sheep farming

Shane Stoner © S. Stoner

New Zealand soils not only feed many sheep, but also store carbon. Shane Stoner uses radiocarbon to investigate how this works – and explains what possibilities there are for improving the carbon storage capacity of the soil to mitigate climate change.

An editorial view from Shane Stoner, Max Planck Institute for Biogeochemistry

In New Zealand, there are about six sheep for every resident of the islands. So, a large proportion of the island nations’ land is dedicated to raising sheep. Sheep eat grass, and humans have developed many ways to grow a lot of grass. However, a growing number of new initiatives are pushing for an increase in the amount of organic matter in pasture soils – for example with decomposing leaves, roots, and other various natural materials. These methods of increasing pasture production are now being optimized for the following goals: to maximize grass production while increasing organic matter storage as a means of combating climate change and improving soil health.

But how can we measure how and if the optimization works? A major tool for studying the storage of organic matter is a fortunate byproduct of nuclear weapons testing: radiocarbon. While this carbon isotope is famously used to determine the age of wooly mammoths and neolithic tools, we can measure specifically the radiocarbon produced by nuclear weapons to measure how long an average molecule of organic matter has been in the soil. We can track changes over time to calculate the rate of carbon flow in and out of soils, and compare these between different strategies for managing water and nutrient supply.

A real-world example involves a sheep grazing research farm near Canterbury, New Zealand, which has one of the most complete annual collections of soil in the world, dating back to 1959. Measuring changes in radiocarbon levels in these soils over time highlights the virtues of moderation in pasture management. A soil that is maintained at moderate water content through irrigation produces almost as much grass as a much wetter soil, but stores almost as much organic matter as a far less productive dry-land soil. Fertilizer behaves the same way: too much fertilizer sends soil bacteria and fungi into an organic matter feeding frenzy, while unfertilized pasture leaves both sheep and microbes hungry. When moderate amounts of water and nutrients are applied, both – organic matter storage and sheep happiness – go up.

As more farmers and ranchers recognize the challenges of climate change, they are seizing on the opportunity for soil stewardship in the face of new obstacles. Advances in soil and climate science are applying accurate tools to quantify the benefits of sustainable strategies. Through the shared expertise of growers and scientists, such work will continue toward a sustainable future for New Zealand's sheep, farmers, and the soil that sustains them both.

This text was created during a workshop by DKK Managing Director Marie-Luise Beck at the Max Planck Institute for Biogeochemistry, in which PhD researchers spent two days working on climate communication.


About the author
Shane Stoner is a PhD researcher at the Max Planck Institute for Biogeochemistry (MPI-BGC) in Jena. He is part of the International Max Planck Research School for Global Biogeochemical Cycles (IMPRS-gBGC) and the Department of Environmental Systems Science at ETH Zürich.


19. february 2020

Picture credits: S. Stoner



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