Grazing and Soil Carbon, Rooting around for an Effect

There is considerable scientific and policy interest in the effect of different grazing methods on soil organic carbon (SOC) and general acceptance that increasing SOC by changing grazing management is possible. While overgrazing is recognised as a cause of land degradation and historical loss of SOC, a review and modelling by Conant and Paustian (2002) showed that ceasing overgrazing and stocking at appropriate levels can also increase SOC. Other reviews showed no difference in animal or pasture productivity between continuous (CG) and rotational (RG) grazing (Briske et al. 2008); and increases, decreases or no change in SOC with high, medium, low or no grazing (Piniero et al. 2010). The variation and sometimes conflicting results of grazing and SOC research is due to the interplay of climate, edaphic factors including current SOC levels (the main drivers of SOC), and management variability; making it difficult to identify a grazing effect. While there have been decades of research on continuous grazing (CG), where stock have ongoing access to pasture, although it may be rested occasionally; and rotational grazing (RG), where stock are moved through a series of pastures which are rested between grazing periods, there has been little research into Holistic Management Planned Grazing (PG). PG mimics large migratory herds using high stock numbers for short grazing periods (days) with long recovery time (months) before a pasture is grazed again