The use of plant growth promoting bacteria for biofertigation; effects on concentrations of nutrients in inoculated aqueous vermicompost extract and on the yield and quality of tomatoes

ABSTRACT Plant nutrient deficiencies can reduce crop development and yields and can be especially problematic in high-yielding intensive crop production systems and when organic materials are used as the only source of nutrients. Aqueous extracts used in organic agriculture, such as compost – or vermicompost-tea, often have deficiencies in macro-nutrients and ionic imbalances. However, when organic materials are used as fertilisers, they are often applied in combination with plant growth promoting bacteria (PGPB), which can improve the availability of the nutrients. In this study, PGPB were used as a tool to facilitate the nutrition of horticultural crops without using synthetic fertilisers. Three bacterial species (Azotobacter vinelandii (AV), Bacillus megaterium (BM) and Frateuria aurantia (FA)) were tested as (i) inoculated to an aqueous vermicompost extract and (ii) applied directly by fertigation to the growing medium in two tomato production cycles. The results showed that it was possible to obtain a balanced nutrient solution, with adequate concentrations of the main nutrient ions, from an aqueous and aerated solution made from vermicompost, without the addition of PGPB. In the second trial, the inoculation with PGPB to the growing substrate for tomatoes fertigated with vermicompost tea, resulted in significant increases in the yield and quality of the tomato fruit, increased nutrient assimilation by the plants and increased enzymatic activity in the growing substrate.