Germination and competition studies on selected weed species in cereal cropping systems in the Western Cape

[摘要] ENGLISH ABSTRACT: The high cost of herbicides for weed control in crop fields in the Western Cape is amajor cause of reducing farmers' net income. As chemical weed control becamemore difficult and expensive, it became necessary to focus on the technique ofreducing weed impact, which does not only involve herbicide usage. Aspects such astillage method, sowing date of crops, crop rotation, weed ecology and germinationrequirements, amongst other, may play a role in reducing weed impact. The firstexperiment was done to determine whether temperature and light had an effect on thegermination of six selected weed species, namely Arctotheca calendula, Avena fatua,Bromus diandrus, Emex australis, Lolium temulentum and Raphanus raphanistrum.Seeds of the aforementioned weeds were collected from Langgewens during 2000 andstored at room temperature before being used in this study. The seeds weregerminated in a germination cabinet at three temperature regimes namely 5 C /15 C,10°C / 15°C and 10°C / 20°C. Most seeds showed a positive germination responseat the 10°C / 15°C treatment, except for Emex australis and Lolium temulentum,which was believed to germinate throughout the year under favourable conditions.Among the germinated weed species, Avena fatua germinated best with a cumulativevalue of 90% as compared to Raphanus raphanistrum, which germinated least with acumulative value of 12%. The second experiment was done to evaluate the effect ofthree growth regulators, namely gibberellic acid, hydroxylamine (auxin), and kinetin(cytokinin) to break dormancy and enable simultaneous germination of the six weedspecies mentioned above. Weed seeds were germinated in a germination cabinet at 20°C using the test solutions of the aforementioned growth regulators. The germinationwas assessed after 3, 7, 10 and 14 days of incubation and the tetrazolium test for theviability of seeds was done for ungerminated seeds. The result obtained showed thatno chemical/concentration proved to be successful in stimulating the germination ofall species tested. As for example a high concentration of hydroxylamine increasedgermination of Emex australis to nearly 100% and inhibited germination of Raphanusraphanistrum to less than 12.5% at all hydroxylamine concentrations. The thirdexperiment was conducted with the aim of determining the competitiveness of the sixweed species mentioned above when grown together with wheat in order to decidewhen weed control will be cost-effective. An additive series experiment wasconducted in a glasshouse. The influence of weed species on wheat plant height, tiller number at different growth stages, vegetative dry mass and gram mass wasdetermined by using different varying weed densities. Weed densities, throughreduction in number of tillers, reduced wheat grain yield. By increasing the density ofwheat this competitive effect could be reduced. Different weed densities caused asignificant difference in wheat plant height, tiller number, dry mass and grain mass.The results showed that species had a significant effect (p < 0.05) on wheat plantheight during tillering, stem elongation and heading growth stages. Total wheat plantabove-ground dry mass was significantly (p < 0.05) reduced by an increase in weeddensity.

[发布机构] Stellenbosch University