ARET, Annual Report 2001, p. 131-3.

The production of tobacco seedlings in soil-less culture introduction

ARET, Agricultural Research and Extension Trust, Lilongwe, Malawi
Methyl Bromide is used as a fumigant to control nematodes in soils, to preserve durable and perishable commodities, to control insects and ants in buildings and vehicles, ships and freight containers and quarantine. In Malawi, it is mostly used as a soil fumigant in tobacco seedbeds and in stored grain products. The chemical is however being phased out because it is one of the products that contributes to the depletion of the ozone layer. The other chemicals include Chlorofluorocarbons (CFCs) and Halogens. As of today, there is no single cost-effective alternative to methyl bromide in all applications. Soil-less culture methods of raising tobacco seedlings by using pine bark, rice hulls, vermiculite and composts as growth media in permanent concrete beds, module trays either suspended on wires or floating on water have been tried in Zimbabwe with success. These materials have not been tested in Malawi the objective of this experiment is therefore to test soil-less cultures as alternative methods of raising seedling. Seedlings were raised in concrete beds, which were filled with the following growing media in various combinations: 1) 50% Composted Pine Bark: 50% Sand (50PB: 50SA), 2) 25% Composted Pine Bark: 75% Sand (25PB: 75SA), 3) 100% Sand (control) (100SA), 4) 50% Rice Hulls: 50% Sand (50RH: 50SA), 5) 25% Rice Hulls: 75% Sand (25RH: 75SA), 6) 50% Compost Manure: 50% Sand (50CM: 50SA), 7) 25% Compost Manure: 75% Sand (25CM: 75SA), 8) 75% Sawdust: 25% Sand (75SD: 25SA), 9) 50% Sawdust: 50% Sand (50SD: 50SA), 10) 25% Sawdust: 75% Sand (25SD: 75SA), 11) 75% Groundnut shells: 25% Sand (75GN: 25SA), 12) 50% Groundnut shells: 50% Sand (50GN: 50SA), 13) 25% Groundnut shells: 75% sand (25GN: 75SA), 14) 25% Compost Madea: 75% sand (25MD: 75SA), 15) Standard control - Methyl Bromide (MeBr). All these growing media were analysed for plant nutrient content before sowing. The experiment was conducted at Kandiya Research station and was laid out in a Randomised Complete Block Design (RCBD) with three replications. There were significant differences in seedling density, plant height, seedling vigour, and weed count and root-knot nematode among the substrates. Some locally available substrates like groundnut shells showed promising results. The trial would be repeated for another season with proper procedures to iron out the shortfalls from the 1999/2000 season.