Die uitwerking van die onkruiddoder Roundup® op sommige populasies van grondmikrobes : oorspronklike navorsing

Die glifosaatbevattende onkruiddoder, Roundup®, word wereldwyd vir onkruidbeheer gebruik. Alhoewel hierdie onkruiddoder beskou word as 'n lae-toksiese (en dus veilige) produk, heers daar tog kommer oor die langdurige effek daarvan op grondmikrobes, plante, diere en die mens. Verskeie artikels in die meer populere media en internet verwys na die gevare van Roundup®. Grondmikrobes speel 'n belangrike rol in die afbraak van landbouchemikaliee. Daar is boere wat sukrose of melasse as 'n voedselaanvulling vir grondmikrobes gebruik. Sommige boere meng dit ook met onkruiddoders ten einde die moontlike nadelige effek daarvan op voordelige grondmikrobes te verminder, deur hulle van 'n eenvoudige koolstofbron te voorsien. Die effek van Roundup®, met en sonder die byvoeging van sukrose, is gedurende hierdie ondersoek bepaal met betrekking tot sommige aspekte van die mikrobiologiese gemeenskappe in die grond. Grondmonsters is by drie geleenthede geneem, naamlik voor behandeling, 'n week daarna en 20 dae daarna. Hierdie grondmonsters is daarrna gebruik vir die meting van kweekbare protosoe (mees-waarskynlike-getal) en metaboliese potensiaal van hoofsaaklik die bakteriese grondgemeenskap (Biolog Ecoplate™), terwyl die filamentagtige groei in situ (versteekte-plaatjie-tegniek) bepaal is. Die byvoeging van suiker het nie 'n betekenisvolle effek gehad op die werking van die onkruiddoder nie. Terwyl Roundup® wel die metabolisme van die grondbakteriee beduidend verander het, het die bakteriegemeenskap na 20 dae, waarskynlik as gevolg van natuurlike prosesse, herstel. The effect of the herbicide Roundup® on some populations of soil microbes The glyphosate, Roundup®, is used worldwide to combat weeds, but knowledge about its effect on soil microbes is limited. Even though this commercially available herbicide is usually seen as environmentally safe, there remain concerns about its long-term effect on soil microbes, plants, animals and humans. Several articles about the supposedly harmful effects of Roundup® are available, especially in the more popular media and on the internet. Soil microbes play an important role in the cycling of mineral elements in the soil and the maintenance of a healthy soil microbe community is of utmost importance to farmers. Some farmers are in the habit of using sucrose or molasses as soil amendments, since the use of these easily obtainable carbon sources as food sources for microbes has been documented. Some farmers add these to their herbicides in order to minimise its possible effect on the beneficial microbial populations. The simple carbohydrate acts as possible substrate instead of the root exudates from living plants that usually act as food source for the microbes. In this study, the effect of the glyphosate containing herbicide Roundup® was tested, with and without added sucrose, on certain aspects of soil microbial communities. The soil was sampled at three stages, namely before treatment, 1 week after treatment and 20 days after treatment. These soil samples were used to measure culturable protozoa (most probable number method) and the potential metabolism of the bacterial community (Biolog Ecoplate™), whilst the filamentous growth (buried slide method) was measured in situ. Adding sucrose did not contribute significantly to the effect of the herbicide on the microbes. Whilst Roundup® did bring about a significant change in the measured potential metabolism of the bacterial community; the effect had worn off after 20 days, possibly as a result of natural processes.