A Cross Sectional Comparison of Chemical Treatment on Plant Biodiversity at Neudamm Farm, Khomas Region

ABSTRACT

This study determined the impacts of chemical application on plant biodiversity in comparison to the control ecosystems over a three-year period at Neudamm farm in Khomas Region, Namibia. In this study, for herbaceous plant sampling, a total of 40 (1m2 ) quadrats were randomly laid in each of the three chemically treated sites (treated in 2015, 2016 and 2017) and in the control site to record the herbaceous plant density, plant species composition, dry matter production and ground cover. For woody plant sampling, a total of three 250 m2 belt transects were randomly laid in each of the three chemically treated sites and also in the control. All woody plants in the belt transects were identified, measured and recorded for plant height and canopy diameters. For soil sampling, a total of ten soil samples were collected from the three the belt transects in each of the three chemically treated sites and also in the control at a depth of 15 cm using a soil auger. The soil was analysed for pH, soil minerals, organic carbon and organic matter. A total of 20 grass species were identified in all the four sites, of which 55% were perennials and 45% were annuals. The mean total grass tuft density was significantly higher (P < 0.05) in control and the chemically treated sites of 2015 and 2017, but lower in the chemically treated site of 2016. Herbaceous biomass production was significantly higher (P < 0.05) in chemically treated site of 2015 (975 Kg DM ha-1 ), followed by 2016 (925 Kg DM ha-1 ) and least in the other two sites. The chemically treated site of 2016 had greater (P < 0.05) ground cover percentage than the other three treatment sites. The total woody plant density was significantly higher (P < 0.05) in the control (14 160 TE ha-1 ) than in all three similar ii chemically treated sites. The canopy cover percentage and woody plant densities in all woody height categories were higher (P < 0.05) in the control and the chemically treated site of 2017, than in the other two sites. The chemically treated site of 2015 had the highest amount of soil pH (6.06), followed by the control (5.61) and the chemical treatment site of 2017 (5.5), and they were statistically significant (P < 0.05). The organic carbon and organic matter percentages were significantly (P < 0.05) higher in the chemically treated site of 2015 than in all the other sites. The soil in the chemically treated site of 2016 had the highest Ca (551 ppm), K (197.3 ppm), Mg (76 ppm), P (23.3) contents, followed by the site of 2015 than in the control. This study concluded that chemical treatments have impacted on the plant biodiversity of the treated rangelands by improving the herbaceous plant species, biomass yields, reduced bush density and enhanced the soil chemical properties.