Maximizing Fish Effluent Utilization for Vegetable Seedling Production by Azospirillum Brasilense

Abstract

Recycling of nutrients from organic sources and modifying farming practices towards sustainable agriculture have gained considerable attention in recent years. This is due to the growing awareness of the declining environmental quality and arable land, and significant depletion of oil and water reserves that drive agriculture production. This study evaluated the impacts of three Azospirillum brasilense strains (i.e. Sp7, Sp7-S and Sp245) on the growth of vegetable seedlings (i.e. tomato, lettuce and cucumber) fertilized with fish effluent. Seeds and seedlings were inoculated prior to germination and transplanting, respectively, and were grown in a greenhouse with natural light. Results show that inoculation with these strains increased root length and endogenous plant IAA (indole-3-acetic acid) of all vegetables. Inoculated tomato seedlings produced bigger leaves, higher dry plant biomass and protein content. Likewise, taller plants with bigger stems and more leaves, and higher fresh plant biomass were documented, but with Sp7 only. Strain Sp245 also triggered an increase of peroxidase enzyme activity. In lettuce, inoculation produced taller seedlings, more leaves and higher peroxidase activity. Chlorophyll and protein content were also increased, but with Sp7 only. In cucumber, inoculated seedlings increased seedling root biomass with higher total phosphorus content and peroxidase activity. Furthermore, inoculation caused little or no adverse impact on the fish effluent bacterial community indicating that these strains can be integrated into production system that utilizes fish effluent as a fertilizer, e.g. Aquaponics. A. brasilense could be a valuable agent to help maximize the usefulness of fish effluent or wastewater from freshwater aquaculture for plant production.