Improving Greenhouse Cucumber Production in De-coupled Aquaponic Systems

Abstract

Cucumbers are a major greenhouse crop, usually grown in hydroponic systems, but can be adapted to aquaponics— the integration of fish and plant production. Aquaponic production has shifted from coupled, recirculating systems to de-coupled, non-recirculating systems due to the ability to adjust water quality parameters, namely pH, in each de-coupled unit to optimize production. In order to effectively adapt cucumber production to aquaponics, determining production practices that minimize production costs and increase yield is necessary. Cucumber production requires energy and labor inputs for the duration of the production cycle, which means costs are likely to increase as production continues even with continued revenue from longer production lengths. To determine a production-cycle length that would maximize profit, four production cycle-lengths were evaluated for cucumbers in a de-coupled aquaponic system. Revenue from cucumber production increased linearly as production cycle length increased, providing the highest revenue at a 95-day cycle length at 17.80 USD per m2. Estimated costs increased as cycle length increased, but the highest profits were obtained at shorter cycle lengths. In aquaponic systems, shortening production cycle length during the traditional off-season for cucumber production would maximize profits. To determine the effect of pH in a de-coupled aquaponic system, a study was conducted using aquaculture effluent from tilapia culture tanks at 4 pH treatments: 5.0, 5.8, 6.5, and 7.0 to irrigate a cucumber crop. Growth and yield parameters, nutrient content of the irrigation water, and nutrients incorporated into the plant tissue were collected over two growing seasons. pH did not have a practical effect on growth rate, internode length or yield over the two growing seasons. Availability and uptake of several nutrients were affected by pH, but there was no over-arching effect that would necessitate its use in commercial systems. Nutrient concentrations in the aquaculture effluent would be considered low compared to hydroponic solutions; however elemental analysis of leaf tissue was within the recommended ranges. Research into other nutrient sources provided by the system (i.e. solid particles carried with the irrigation water) would provide further information into the nutrient dynamics of this system.