Recycling of spent mushroom substrate through its use in crop production as a component of growing media would provide an environmentally safe disposal. Therefore, the aim of this study was to determine the suitability of composted and un-composted oyster mushroom (Pleurotus ostreatus) spent substrates mixed with organic red sandy soils, as potting medium for tomato (Solanum lycopersicum). Also to determine the effect of these mixtures on plant parasitic nematodes. The study was conducted at the Agricultural Research Council-Plant Protection Research Institute, Roodeplaat, during March to May 2011 and 2012. Plant growth parameters included plant height, fresh mass yields as well as stem and leaves dry mass. For tissue and substrate mineral content, the analysis of P, K, Mg, Ca, S, Mn, Fe, Cu and Zn content were analysed. Analysis also included establishment of nematode populations as well as physical properties such as electrical conductivity, air-filled porosity and water-holding capacity. The results showed that plant growth and dry mass yield was significantly higher in the composted spent substrate compared to that in the un-composted spent substrate treatment. None of the spent mushroom substrates had dry matter yield of tomatoes. However, symptoms of nematode attack were found on roots of the control, but not on the treatments which received spent mushroom substrates. The number of bacteriovores and fungivores was higher in both the spent substrate treatments compared to that in the control. These results indicate that spent oyster mushroom substrate as soil amendments promote growth and activities of microorganisms that are antagonistic to plant-parasitic nematodes.

Keywords: Bacteriovores, fungivores, Solanum lycopersicum, plant-parasitic nematodes, Pleurotus ostreatus, spent mushroom substrate