AQUAPONIC TILAPIA/CUCUMBER PRODUCTION VARYING PLANT DENSITY AND SUBSTRATE  

Cucumbers (Socrates variety) are a popular hydroponic/aquaponic greenhouse vegetable, especially where production space is at a premium.  By planting more plants per square foot, growers could potentially double production within the same footprint. Also, the standard substrate for cucumbers production in Dutch buckets has been perlite, an expensive obsidian rock product. By contrast, pine bark is an inexpensive, abundant and locally available material, at least in the Southeast US. Thus, increasing plant density and substituting pine bark for perlite in the greenhouse production of cucumbers could reduce costs and increase returns.

This project integrated tilapia and cucumber production to supply Auburn University Dining Services with fresh, locally grown products for their student cafeterias.  In mid-October, eight weeks prior to planting cucumbers, one 12' x 88' raceway was stocked in with 11,000 tilapia fingerlings averaging 100g each.  Fish were fed a 40% CP feed until reaching a 150g weight, then protein was reduced 36%.  A total of 3,742 lb of 450g tilapia ($7,484) were harvested from January through August 2016.  Approximately 500 gallons per day of fish effluent was directed to the plant greenhouse cucumber production.

A 36-week density-substrate factorial experiment was conducted with cucumbers in a greenhouse using fish effluent as the sole water-nutrient source. One experimental block included cucumber transplants being planted in Dutch buckets with either pine bark or perlite substrate at a density of one or two plants per bucket with 15 replicates per treatment.  The greenhouse was divided into 5 experimental blocks, each containing a total of 60 spaces or Dutch buckets, broken into 4 equal rows of 15 plants with a randomized placement.  Cucumbers from the central 5 plants of each row were counted and weighed individually. Each experimental block stayed at least 50 days and no experimental block stayed more than 100 days.

After 36 weeks, cucumbers planted at a density of two plants per Dutch bucket had significantly higher total yields than cucumbers planted at a density of one plant per bucket. Total yields from cucumbers planted in pine bark showed no statistical differences from total yields from cucumber plants planted in perlite.