Mesofaunal assemblages in soils of selected crops under diverse cultivation practices in central South Africa, with notes on collembola occurrence and interactions

English: Soil is a complex medium, comprised of both biotic and abiotic components. Interactions between these components are responsible for the beneficial services provided within different ecosystems. The biotic component, which is also referred to as the active role players in the soil, is responsible for these services. The incidence of these organisms is influenced by the abiotic factors, which act as filtering mechanisms that select for certain species to occur within certain areas. Considering an ever-increasing human population, these services could prove beneficial, since it could improve crop yields at minimal cost without exploiting the soil resource. Many farmers are now changing their farming methods to more sustainable and conservation focused practices to try and reduce the disruption of soil community structures and to optimize the complexity and resilience of these communities. Disturbances lower the complexity of soil communities and therefore limit the services that could be provided. This study focused on the fluctuations in diversity of selected role players within the soil medium due to the presence of certain agricultural practices and environmental changes. Sampling for this project was conducted at six localities in the Free State Province between 2011 and 2014. Three of the localities are located in the Nama Karoo Biome and the other three in the Grassland Biome. The farms Vaaldam, Koppieskraal, Thornberry and Klein Brittanje were selected due to the diversity of agricultural practices and management strategies applied. The rest of the localities were the Paradys Experimental Farm, which is the experimental farm of the University of the Free State, where a pesticide trial was conducted and the farm Eureka, which was exposed to pollutants from a goldmine tailings dam. The variation in events and the general environment posed the perfect opportunity to observe and evaluate fluctuations in the diversity of the selected faunal groups within the relevant soils. Sampling was conducted in the porosphere of each plant. All the plants selected for sampling were in optimal condition and away from the edges of the field. Samples were marked and transported to the lab where the organisms were extracted by means of the Berlese-Tullgren funnel extraction method. Sorting and identification were subsequently completed from which a reference collection was compiled and stored in ethanol. Fluctuations in the diversity of the selected fauna was observed throughout this study. Agricultural practices had a definite influence on the severity of these fluctuations. Mechanical and chemical disturbances usually had a reduction effect on the diversity at first, which was followed by an increase in the abundance of certain opportunistic species. In some cases, these increases were quite severe, since certain species would flourish in the absence of competition and predator pressure, especially in the case of introduced species. Incorporation of stubble into the soil should be carefully managed, as this could create problems such as compaction. In spite of a certain degree of compaction, it was still found that soils with a higher organic component were more resilient in the presence of disturbances. Stubble-burning influenced the vertical distribution of soil mesofauna due to the condensation effect of such an event. The influence of chemicals depend on the persistence of the chemical used, as well as the complexity of the community before exposure. In already compromised areas, the effect of chemicals were far more detrimental to the community structure than at a natural site where a single application was done. The effect of pollutants from a tailings dam reduced the diversity considerably and only a few species were present at these sites. For species to occur within this heavy metal polluted area, they must be able to either tolerate or avoid the pollutants. It was clear that each locality with its specific influencing factors selected for certain species to be present. Fields that were minimally disturbed and where organic materials were incorporated into, the soils had a higher tolerance to disturbances. This was due to a more complex community structure within the soil, thus indicating that even in the presence of a disturbance, these soils could still provide services.