7 August 2012
We were pleased to see that the “What’s Your Beef” report stimulated some interest and comments from Professors Smith and Goulding (FCRN Newsletter, Mailing 31 May 2012). However, on reflection, there are some points arising which we feel need clarification.
We asked Best Foot Forward to construct scenarios to include potential carbon sequestration under grassland use, because we considered the omission of sequestration and land use changes from standard methods was unsatisfactory. Obviously the value used for SOC gain will affect results, which is why a published value, 0.24tC/ha/y, from the Janssens et.al (2005) paper was used. Professor Smith was a co-author of this paper, and he quotes a similar value of 0.22tC/ha/y from his 2008 paper.
Professor Smith mentions “SOC accumulation rates supposedly found at the farms in Northumberland” –there were no Northumberland farms in the beef study. We made reference in passing to a 2010 study of land management for soil carbon at the National Trust Wallington Estate in Northumberland which showed the impact of farm management on soil carbon stock, and we suggested it would benefit land managers to use soil analysis to determine the carbon status of their own soils. In the Wallington report, Madeleine Bell estimated that if all rough pasture on the estate (a total of 1200 hectares) could achieve optimum soil carbon, an annual sink equivalent of up to 21,500 tonnes CO2 might be achieved over a period of 20 years, and that the gains from good grassland management have the potential to outweigh soil carbon losses from limited conversion to arable. If we understand this estimate correctly, this is equivalent to about 5tC/ha/y.
The reference in “What’s Your Beef” to soil carbon stock increases of 3-5tC/ha/y was based on calculations made by individual farmers – in one case the soil carbon status was monitored over a period of seven years. Questions arise about the influence of sampling frequency, arable reversion, manure applications and grazing system on the results, but the calculations from SOM to SOC appear correct and accounted for bulk density. We did point out that such amounts were an order of magnitude greater than amounts typically reported in the literature, that it followed that more information is needed about soil carbon changes under carbon-friendly management, and that we would address this by experiment under real farming conditions. However, it is also worth noting that a range of C sequestration values from 0.11 to 3.04tC/ha/yr was reported by Conant, R.T. et al (Ecological Applications, 11(2), 2001, pp. 343–355. Grassland management and conversion into grassland) who concluded that grasslands can act as a signiﬁcant carbon sink with the implementation of improved management. This paper is cited several times in IPCC AR4 Ch 8, 2007.
We felt the scenario building provided an insight into what evolved LCA methods might show in the future with regard to the merits of different livestock production systems. The Eblex “Down to Earth” report (2012) indicates the desirability of movement in this direction, and we note also that Defra project SP1113 is calling for research to develop a framework for capturing cropland and grassland management impacts on soil carbon in the UK LULUCF inventory and to calculate mitigation and offset potentials through changing cropland and grassland management in the future.
Our report illustrates that accounting for carbon emissions alone can be highly misleading when comparing different farm systems and that methodologies that include land use change and sequestration give a more rounded picture of how carbon features in farm systems.
Rob Macklin, Food and Farming Specialist
John Kay, Farm Wastes and Resources Consultant
The National Trust, Heelis, Swindon