Optimal spatial and temporal utilization of grassland resources for extensive livestock production.

Abstract

South Africa naturally experiences variation in rainfall patterns with distinct seasonal distribution. The anticipated disruptive effects of climate change, in this region, on vegetation dynamics is likely to accentuate the impact of seasonal forage nutrient fluctuations on livestock production. Although there are several grazing philosophies that have been adopted to mitigate these constraints (continuous and variations of rotational grazing systems), debates on superiority between these systems continue to be of interest to researchers and livestock producers. Nonetheless, continuous grazing systems have largely been condemned due to the detrimental effects of extensive selective grazing on vegetation composition and soil conservation. Poor implementation of these systems has resulted in extensive veld degradation, significantly reducing sustainability of livestock production. This is more pronounced in communal rangelands where production capital is limited. Moreover, erratic rainfall and extreme temperatures have resulted in the abandonment of large areas of croplands, and thus further impacting negatively on livestock production dynamics. Therefore, it is necessary to quantify utilization regimes of the abandoned crop lands, continuously and rotationally grazed veld and examine their effects on ecosystem health and livestock production. To examine these effects, a study was conducted in Mzongwana, Matatiele (old lands and continuously grazed veld) and in Wakefield Research Farm, Fort Nottingham (rotationally grazed veld). In each site, six 100m line-transects were laid and a 0.5 by 0.5m quadrat were placed in 2m intervals along each transect. In each quadrat, sampling for species composition, biomass accumulation, and bulk forage quality were sampled. Along each transect, soil samples were collected at 0-15cm depth at 25m intervals and analysed for soil fertility. To examine the influence of forage utilisation intensities, as affected by the previous management, seasonal nutrient dynamics, data were collected during summer (November, January, and April) and during winter (June and August). The results revealed that species composition and biomass accumulation had a direct influence on forage quality, while grazing systems mostly affected soil fertility. Additionally, the results confirmed that previous cultivation has a negative effect on soil organic carbon (C) and nitrogen (N) concentrations, and revealed a significantly high mineral variation between seasons. These variations were also evident in the nutrient accumulation in the forage, with distinctively high crude protein (CP) and low acid detergent fibre (ADF) and neutral detergent fibre (NDF) in early summer. Therefore, to effectively utilize the old lands towards improved livestock production, grazing should be during early to mid-summer. On the other hand, despite soil nitrogen in the continuously grazed site being lower than the rotationally grazed site, CP was significantly higher and steadily declined over the season. Therefore, suggesting that biomass accumulation has a negative influence on forage quality. Moreover, lower forage quality in the rotationally grazed veld was largely attributed to extended rest periods which allowed grass to mature, thus reducing the overall quality. Based on these findings, it can therefore, be recommended that the old lands be grazed during the early to mid-summer and rested during late-summer. This will improve nutrient availability for livestock and will allow for seeding rest to improve succession rate. Moreover, the continuously grazed veld is recommended to be grazed interchangeably with the old land, that is, in winter. As a result of slow crude protein decline in the continuously grazed veld, grazing in winter will improve livestock morbidity and mortality resulting from low forage availability. Finally, in the rotationally grazed veld high intensity grazing should be incorporated in the grazing systems employed to reduce biomass carryover and keep forage low and nutritious, as this veld in a high rainfall area.