High-density grazing on semi-arid grassland scrutinised

A study by University of the Free State researchers who compared high-density grazing to conventional rotational systems has underscored the complex interplay between grazing management, climate, and soil properties in determining soil carbon and vegetation dynamics

-  Roelof Bezuidenhout

Promises of veld improvement and higher production, coupled with private carbon certification schemes offering farmers who apply high-density grazing credits from carbon sequestration, have underscored the lack of knowledge about the pros and cons of these systems, as well as how much carbon grassland can realistically store under South African conditions.

The study 'Grazing management and edapho climatic factors: drivers of soil carbon and vegetation dynamics in South African rangelands' by Elmarie Kotzé et al measures soil and vegetation differences between high-density and conventional rotational grazing systems on commercial rangeland farms in four districts in the summer rainfall regions: North West (around Louwna village), the Eastern Cape (Molteno), the eastern Free State (Reitz), and the central Free State (Bloemfontein, Dewetsdorp).

For the study, a fence-line comparison was done on 11 sites, each representing two neighbouring commercial rangeland farms in the four localities. In each case, soil and vegetation were observed on both sides of the fence between the farm practising high-density grazing and the farm practising conventional grazing.

The study showed that in regions with greater rainfall, cooler temperatures, and finer soils, as in the central and eastern Free State, high-density grazing (HG) often had positive (sometimes even substantial) impacts on soil carbon, root biomass, soil microbial activity, and vegetation, suggesting greater vegetation productivity and carbon sequestration on these farms. Conversely, in drier regions, such as the North West, with sandier soils, benefits from HG on soil properties were less pronounced.

While products from improved root growth under HG systems enhanced soil microbial activity and carbon sequestration, a significantly negative impact of increased stocking rates on bulk density, particularly in deeper soil layers, was found across all regions surveyed.