Do Algae Cause Growth-Promoting Effects on Vegetables Grown Hydroponically?

Fertigation systems, especially hydroponic systems with recirculating nutrient solution, are an ideal environment for algal growth, but it is not clear if this contaminant affects the crop. Therefore, greenhouse experiments were carried out to monitor the development and composition of algae, as well as their effects on lettuce and cucumber performance. In addition, several different substrates and water sources, with differing algal communities, were tested for their effects of on both algae growth and crop performance. In open troughs, algal density was lg 4.2 to 4.6 cells/ml in the lettuce and lg 3.7 to 4.6 cells/ml in the cucumber experiment. Algal density and composition were mainly influenced by initial density in the different water sources. Moreover, plant species, temperature, and concentration of the nutrient solution also affected the density. The diversity of the algal community was poor; only unicellular species were observed with Chlamydomonas spp. and Pseudodictyosphaerium spp. as main representatives in the drain water. Cucumber and lettuce shoot fresh weight, and therefore lettuce yield, were reduced significantly in the presence of algae, but cucumber yield was not affected. Overall, the present results indicate that the effects of algae depend on several factors, and therefore do not enable generalization on whether algae have a negative or positive impact on crop growth in hydroponic systems.