Evaluating Water Use and Yield of Greenhouse Tomato as Affected by LED and HPS Supplemental Lighting during Winter Months

Many growers employ hydroponics for growing high value crops, where plants are cultivated in a soilless substrate with the vast majority of nutritional requirements supplied via the irrigation water. The traditional concepts of surplus irrigation and fertilization conflict with the environmental aspect as it can lead to over irrigation and ground water pollution. In the current study, supplemental lighting was used for commercial high wire tomato production during winter months and the plants were fertigated based on commercial practices with 30% leaching fraction. Main objectives of this study were to compare water use of high-wire grafted tomato grown with and without supplemental lighting and to evaluate the impact of light qualities and light sources [traditional overhead high-pressure sodium (HPS) lighting lamps vs. light-emitting diode (LED) intra-canopy lighting towers] on several production parameters for a commercial tomato cultivar under greenhouse environment. Leachate volume was measured on alternating days and daily water use (DWU) was calculated from each slab planted with a single plant which was subtracted by evaporative water loss measured from a slab without a plant. The light treatments were composed of LED treatments receiving three different combinations of red (R), blue (B) and far red (FR). Light treatments consisted of Blue (100B:60R:0FR), Red (0B:100R:0FR), 50% Far-red (0B:100R:50FR), Far-red (0B:100R:100FR), and HPS and un-supplemented controls. DWU increased with crop development stages. All light treatments followed the same trend on DWU with the highest water use during the periods of fruit development to harvest initiation. DWU was highest for HPS control and lowest for un-supplemented control. Among the LED treatments, highest DWU was observed in Red (0B:100R:0FR), followed by Far red (0B:100R:100FR) and then Blue (100B:60R:0FR). Variations in DWU were associated with leaf area, biomass production and fruit yield. Fruit yield was similar between LED and HPS treatments with highest fruit yield was obtained in Far-red (0B:100R:100FR). Fruit cluster size increased with addition of FR to R. High DWU in HPS was attributed to increased evapotranspiration demand due to heat generation under the overhead HPS lamps compared to plants grown using LED. It is concluded that supplemental LED with Red (0B:100R:0FR) and Far-red (0B:100R:100FR) can reduce water use for greenhouse tomato production and produce as equal or better tomato yield and quality compared to HPS.