Effect of freshwater sapropel on plants in respect to its growthaffecting activity and cultivable microorganism content

Abstract

A positive effect of organic-rich sediments sapropels on plant growth has been suggested in general, but has not been proven on an experimental basis. The aim of the present investigation was to study biological activity of freshwater sapropel and its product including analyses of plant growth-affecting activity and cultivable microorganisms. Besides mineral nutrients, sapropel contained unspecified substances promoting plant growth in a seedling growth test with beetroot, Swedish turnip, carrot and tomato. Summed plant growth-affecting activity of sapropel and sapropel-containing substrate BioDeposit Agro had a relatively high growth-enhancing component together with an extremely low growth-inhibiting component. Substrate amendment with BioDeposit Agro resulted in a significant increase in dry matter accumulation only in lettuce plants but not in winter rye plants. High level of aerobic heterotrophic bacteria, high level of yeasts and variable level of filamentous fungi with a low diversity were found in all sapropel samples tested. Plant growth-stimulating activity negatively correlated with the number of colony forming units of both yeasts and fungi. There was no correlation between the number of bacteria and plant growth-stimulating activity.