Effects of plant growth-promoting rhizobacteria and olive waste compost on organic tomato seedling production

The aim of this experiment was to evaluate composts produced from by-products of olive oil production as a constituent of growing media and to improve seedling growth with plant growth-promoting rhizobacteria (PGPR) in organic tomato seedling production. Two composts, two-phase (2POMW) and three-phase (3POMW) olive mill wastes with separated dairy manure, poultry manure, and straw using aerated static pile composting methods were produced. Composts obtained from 2POMW and 3POMW are named as C1 and C2, respectively. C1 and C2 were separately enriched by rock phosphate and potassium salt (EC1 and EC2). In this experiment, 25 and 50% compost rates were selected based on our previous results and used to mix with local peat (LP), respectively. Treated seeds with Bacillus subtilis ( strain 66/3) and Pseudomonas fluorescens (strain 112) were sown on March 7, 2017. Peat (100%) and non-PGPR treated seeds were used as controls. Each treatment had 4 replicates and each replicate included 64 plants in a tray with a volume of 33 mL each. After 3 days in germination room in dark at 24 degrees C, seedlings were moved to a greenhouse. Some physical and chemical properties of each growing medium, germination rate and period, seedling vigor, leaf color and chlorophyll content (SPAD) were determined. The effects of PGPRs and growing media on many measured parameters were found statistically different. The treatment 25% EC1+75% LP mixture gave the highest seedling biomass, germination rate and period followed by 25% EC2+75% LP. Olive mill wastes had a higher chlorophyll content, seedling height, shoot fresh weight and root and shoot dry weights than peat. It was concluded that usage of enriched composts with a rate of 25% could be an alternative to reduce the amount of peat in organic tomato seedling production and their effects can be improved with the use of either B. subtilis or P. fluorescens.