Guide by Duchy College, Plymouth Uni, Rothamsted Research and Farm Carbon Cutting toolkit setting out how best to take soil samples, what to ask of the labs and how to interpret soil carbon measures.

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Practical guide to monitoring soil carbon launched

A new practical guide to assessing soil carbon promises to answer farmers’ key questions at a time when many are looking to understand their soil health.

Produced by Duchy College, Plymouth University, Rothamsted Research and the Farm Carbon Toolkit, the guide lists and answers key questions for robust on-farm monitoring of soil carbon and associated indicators of soil health. This is particularly significant given the recent announcement of the Sustainable Farming Incentive scheme, which is reliant on a consistent approach to soil sampling.

“In the Soil Carbon Project we were trying to understand the relationship between farm management practices and levels of soil organic matter, as well as issues around how we monitor soil carbon,” says Stephen Roderick, project management at Duchy College.

Carbon sequestration plays a key part in climate change mitigation, but soil carbon’s importance goes beyond sequestering as much as possible, says Andy Neal, research scientist at Rothamsted. “What’s much more important are the co-benefits of getting organic matter into soil – organic matter affects how much water and nutrients the soil can store, and can limit the carbon footprint,” he says.

So what tips does the guide include?

Soil sampling - timing

“Traditionally the sampling periods are the spring and autumn,” explains Becky Willson, business development and technical director at Farm Carbon Toolkit.

“We have been looking at what’s happening at different depths, zero to 10cm, 10 to 30cm and 30 to 50cm; the important thing is to avoid sampling after cultivation, particularly if it has been ploughed. Leave the fields to settle after cultivation for at least three months,” she adds.

Farmers should sample at the same time each year because seasonality can affect results. “If sampling just for organic matter, in theory the soil can be sampled at any time of year but be consistent with that approach. And if you’re sampling for nutrients at the same time, think about when that fits in best in rotation management.”

Location

When it comes to sample location, it’s best to select fields which represent the variation across the farm, including differences in soil texture, cropping and management, says Ms Willson.

There are three main options for sampling patterns within a field: Sampling in a ‘W’ configuration, in a linear transect or a grid formulation. The guide recommends at least five sample points although 15 is preferable. Samples can be aggregated but only on a field or zone basis and they must be well mixed before bagging.

Equipment

In terms of equipment, a soil auger is the best implement for the job – but digging a hole and removing soil by hand is fine. Clean buckets and sandwich bags are also necessary for collecting the samples.

Farmers should send the samples off as soon as possible, although up to two weeks’ delay is acceptable if they are refrigerated – this slows the organic matter breakdown.

Analysis

In the lab, there are a couple of options for testing organic matter and soil carbon – Loss on Ignition (LOI) and DUMAS. “LOI provides a rough idea of the soil organic carbon content and is generally slightly cheaper, however it is not standardised between labs making it crucial to stick with the same lab,” explains Jasper Newman, researcher at the University of Plymouth.

The practical guide, which is based on the latest research, will help farmers, advisers and researchers to adopt the most consistent techniques for monitoring soil carbon – which will become increasingly important as focus on carbon intensifies, says Mr Roderick. “Robust estimates of soil carbon stocks can be a complicated subject; this guide is designed in collaboration with our research partners to answer those key questions.

“The learnings from the project have informed the Farm Net Zero project and now that the Soil Carbon project has come to a close, it's activities will continue in Farm Net Zero with the support of the National Lottery Climate Action Fund.”

Abstract

1. Introduction and aims

This guide was produced as part of the Soil Carbon project and was written as a collaboration between Duchy College, Plymouth University, Rothamsted Research and the Farm Carbon Toolkit. The work was supported through the Agri-tech Cornwall & the Isles of Scilly Project, an £11.8m project to increase Research Development and Innovation in the Agri-tech sector across Cornwall and the Isles of Scilly. Running to December 2021, it is part-funded by the European Regional Development Fund, Cornwall Council and the Council for the Isles of Scilly (award number: 05R16P00366). For more information, please see www.agritechcornwall.co.uk.

This guide lists and answers key questions for robust on-farm field monitoring of soil carbon and associated indicators of soil health. This guide will be relevant to farmers seeking to measure and understand their soil carbon stocks - as well as landowners, advisors and researchers supporting them. Supply chains and organisations seeking to reward farmers for improving soil carbon stocks will also find this guide helpful, however it does not act as a standard or protocol. The guide will be accompanied with detailed supplementary materials stemming from the ERDF Agri-Tech Cornwall funded “Soil Carbon Project”(2018 to 2021).

The Soil Carbon Project worked with farmers and growers across the UK to refine soil sampling methodologies, and develop farm-level information on the best practices that will create a system where soil carbon sequestration plays a key part in climate change mitigation efforts. The research team is immensely grateful to the 85 farmers who engaged in the project. The guide consists of answers to the following core questions:
1. When to conduct your soil carbon sampling?
2. What fields to select on your farm?
3. How to sample within those fields?
4. At what depths should samples be taken?
5. How often should you repeat your sampling?
6. How to collect and prepare your samples?
7. What are the options for the lab analyses?
8. What are the main soil health indicators that should be monitored?
9. What are the outputs and benefits?

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