Improving cantaloupe fruit sugar content in the UVI Commercial Aquaponic System
Controlled water stress imposed during the reproductive stage of fruit crops are well-known for increasing flowering and fruit quality. However, deficit irrigation is challenging to apply on recirculating aquaponics systems due to the use of deep water hydroponic troughs for vegetable production. Our study evaluated the effect of partial root and canopy cut performed before two different harvest schedules on cantaloupe fruit sugar content. The UVI Commercial Aquaponic System used consisted of three main components: fish rearing, solids removal and hydroponic vegetable production troughs. The hydroponic troughs were 30×1.2×0.3 m with a volume of 11.3 m3 and a surface area of 214 m2. The water flow rate on the troughs was 125 L/min for a retention time of 3 h. Fish waste products were the source of nutrients for plant growth. Three-week old cantaloupe 'Goddess' seedlings grown on peat-based substrate were transplanted into 1.2×2.4-m (2.97 m2) Styrofoam® rafts on the aquaponics system on Oct 2, 2015 (day after transplanting, DAT 1). We planted 2 plants/raft spaced every 1.2×1.2 m in a density of 1.485 plants/m2 and used 12 rafts/trough. Our treatments were the combination of partial root and canopy cuts (0%, 25%, 50% and 75%) in two harvest schedules (10 days after cutting or at fruit maturation), resulting in 20 treatments, in a CRD with two replications. The root and canopy cutting was performed on DAT 37. The first and last harvest were performed on DATs 47 and 64. Sugar content increased only on the treatments with no root cut, 75% and 25% of canopy cut and fruits harvested at the maturation (9.1 and 8.4°Brix), with a negative effect on the treatment with 75% of root cut, no canopy cut and fruits harvested at the maturation (3.7°Brix) (p=0.0060). The treatment with no root or canopy cut and fruits harvested at the maturation promoted the highest yield (30,227 kg/ha), indicating a negative effect of the partial cutting on fruit total yield (p=0.0072). No treatment response was found on fruit length and width, fruit hardness, fruit pulp thickness, leaf chlorophyll and anthocyanin content, root and shoot dry weight and shoot fresh weight (p>0.05). Even though our results indicated an increase in fruit sugar content, more research is necessary to develop an alternative cultural practice for increasing cantaloupe fruit sweetness in aquaponics without compromising total yield.