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School of Geography

Land management impacts on carbon sequestration and storage on upland grasslands

Background & value to industry
Acid and improved grasslands cover much of upland Britain and their use for sheep grazing is important to local rural economies.  Grasslands store considerable amounts of carbon (C) in their topsoils and contribute more than 32% of the total C stored in British topsoils, second only to peat bogs (Ostle et al., 2009).  It is important therefore that we understand how best to manage upland grasslands not only to support livestock and rural economies, but also to preserve and accrue soil C stocks.

Soil C sequestration occurs when soil C inputs from grass productivity outweigh soil carbon outputs (as gaseous and soluble losses) due to soil decomposition.  Management to increase grass productivity, for example through fertilizer and lime additions, therefore has the potential to increase soil C storage.  However, there is a lack of evidence to support this theory, and where evidence does exist it is sometimes contradictory.  For example, in long-term plot experiments at lowland grass sites, over a century of liming was shown to increase soil C by 2-20 times compared to unlimed grassland (Fornara et al., 2011).  In contrast, experimental evidence from limed upland grassland in Scotland suggests that more C is lost from the soil due to microbial processes than is accrued and returned to the soil via plant biomass (Rangel-Castro et al., 2004).  Even less information is available on the impact of N fertilization or organic (slurry) amendments on net soil C accrual in grasslands since research in these areas has up until now mostly focussed on drainage water quality.  Nevertheless, there is some evidence that dairy slurry applied to grassland causes an increase in losses of soluble C, implying that soil C retention is reduced (Bol et al., 2004).  There is, therefore, an urgent need for evidence to inform land managers and policy makers on i) the current stocks of C in upland grasslands, and ii) the influence of management on C accrual in grasslands.  

Aims and objectives
The aims of this project are to quantify soil C storage in a region of upland grassland in North Yorkshire, and to investigate the effect of liming and fertilizing on grassland C accrual. The specific objectives are:

  • What is the current C stock of grasslands in North Yorkshire;
  • Whether a relationship exists between landscape-level soil C pools and current grassland management;
  • What are the impacts of liming, inorganic fertilizer and slurry application on i) biomass productivity; ii) gaseous C losses; iii) soluble C concentrations in grasslands;
  • What are the impacts of management on the overall carbon mass balance?

Approach and programme of work
This project will be achieved through a combination of field survey, statistical modelling, and field and laboratory manipulation experiments.  The student will develop their own work programme in consultation with supervisors and a research support group consisting of at least two additional non-supervisory researchers. 

Bol, R., Kandeler, E. , Amelung, W. , Glaser, B., Marx, M.C. , Preedy, N.  & Lorenz, K. (2003) Short-term effects of dairy slurry amendment on carbon sequestration and enzyme activities in a temperate grassland. Soil Biology & Biochemistry, 35, 1411-1421

Fornara, D.A. , Steinbeiss, S. , McNamara, N.P., Gleixner, G. , Oakley, S., Poulton, P.R., Macdonald, A.J.  & Bardgett, R.D. (2011) Increases in soil organic carbon sequestration can reduce the global warming potential of long-term liming to permanent grassland. Global Change Biology, 17, 1925-1934

Rangel-Castro, J.I. , Prosser, J.I., Scrimgeour, C.M. , Smith, P. , Ostle, N., Ineson, P. , Meharg, A.  & Killham, K. (2004) Carbon flow in an upland grassland: effect of liming on the flux of recently photosynthesized carbon to rhizosphere soil. Global Change Biology, 10, 2100-2108

Ostle, N.J., Levy, P.E. , Evans, C.D. & Smith, P. (2009) UK land use and soil carbon sequestration. Land Use Policy, 26, S274-S283