Effect of different soilless growing systems on the biological properties of growth media in strawberry

Composts produced from different types of agricultural residues can be a suitable material for growth media or for use in field soils as amendment. The use of these composts in soilless growing systems (SGS) can improve sustainability. Using a randomized complete block design with three replicates, three growth media were compared in three soilless systems in two bioassays. Growth media compared were a composted cork thin waste mixed with rice hulls (2:1 v:v) (CCR), a peat growth media (P), and a coir fibre (CF). The soilless growing systems used were: open (O), closed (C) and closed with slow sand filtration (CSSF). Growth media microbial activities were determined by the measurement of β-glucosidase activity at the beginning of the bioassays. Physicochemical properties of the growth media were evaluated at the beginning of the bioassays. Microbial community profiles were determined by dilution plating on semi-selective media. Microbial activity and pH were higher in CCR than in P and CF. Electrical conductivity was lower in P than CCR and CF. At the beginning of the assays, Bacillus spp., and oligotrophic actinomycetes were higher in CCR than in P and CF. At two and a half months after transplantation, Bacillus spp., copiotrophic bacteria, oligotrophic actinomycetes, cellulolytic bacteria and oligotrophic bacteria were higher in CCR than in P and CF. In the CSSF system, the population of copiotrophic bacteria was the only cultivable group that was different to the other systems that were evaluated (O and C). The CSSF system reduced the fungal population. However, the highest fungal population was detected in the O system. The copiotrophic bacterial population was higher in rhizosphere than outside rhizosphere. Therefore, the growth medium and the system of soilless culture have significant effects on the population profiles of microorganisms in the rhizosphere.