The efficacy and safety of bromacil based herbicide for the control of the invasive bush species in South African rangelands

The use of bromacil based herbicides in agriculture and environmental management is a growing practice with economic importance. Bromacil possesses broad toxicity to many plant species, although, different formulations exist that are used for different purposes in farming systems. There is increasing concern about its use for the control of invasive woody species on South African rangelands; especially its effects on non-target grasses, broad leaved plants and other bioticcomponents of the rangeland ecosystem. This review outlines the importance of bromacil use, its nature and activities as an ingredient in herbicide formulation and the effects of its use on biotic andnon-biotic components of rangeland ecosystems. The current use of bromacil based herbicides for the control of bush encroachment seems necessary to derive good productivity from encroachedrangelands and reduce cost and drudgery associated with other methods of bush control. Bromacil is absorbed through the plant’s root system and translocated upwards via the xylem vessels to theleaves, where it interferes with light harvesting complexes and disrupt the photosynthetic pathways of the plant. This kills the plant slowly; sometimes, it spans over two years. Bromacil could be persistentin the environment for the same length of time, depending on the application method, the target species and the soil properties at the application site. Bromacil has a very low mammalian toxicity, but isconsidered to be slightly toxic to fishes and amphibians. The effect of Bromacil on soil microbial population depends on the exact formulation, concentration and microbial species in question. Yet, bromacil is degraded by microorganisms in the soil and water, portions that escape into open water bodies are also degraded by photo-oxidation reaction. While bromacil provides for sustained weed control, its persistence in the environment and low degradation rates, is a cause for concern

Physicochemical characteristics of communal rangeland soils along two defined toposequences in the Eastern Cape, South Africa

To proffer a sustainable solution to rangeland degradation, an understanding of the innate soil properties is vital. This study investigated the relative association of surface (0–20 cm) soil physicochemical properties, viz. electrical conductivity, cation exchange capacity (CEC), soil organic carbon, available phosphorus, particle size composition, soil aggregate stability and microbial respiration, along a toposequence in two vegetation types. The study sites and vegetation types were Magwiji (Lesotho Highland Basalt Grassland) and Upper Mnxe (Tsomo Grassland). In each site, we identified three experimental units along toposequence delineation, classified as crest, midslope and valley bottom. Vegetation type significantly (p < 0.05) affected sand fraction, aggregate stability under fast wetting, and mechanical disaggregation and CEC. Toposequence delineation significantly (p < 0.05) affected fast wetting, slow wetting, mechanical disaggregation, microbial respiration and CEC. There was significant variation and relationship between vegetation types, toposequence delineation and soil properties. The results suggest that toposequence delineation more than vegetation type influences soil property rangelands; therefore, in determining site-specific management techniques for communal rangelands it is important to consider the direction and magnitude of these relationships.African Journal of Range & Forage Science 2010, 27(2): 89–9