GREENBOX Technology II - Comparison of Environmental Conditions, Productivity, and Water Consumption With Greenhouse Operation

Abstract

Highlights Increasing population, demand, and urbanization have increased food security pressures. We compared GREENBOX with a greenhouse for urban crop production. GREENBOX and greenhouse provided the required environmental conditions and comparable biomass output year-round. GREENBOX performance is comparable to a greenhouse for urban crop production but with more advantages. Abstract. The Yang Laboratory at the University of Connecticut has developed the GREENBOX technology for growing fresh produce in urban areas to meet the increasing demand for sustainable and local food production. Previous studies have shown that GREENBOX units can provide the desired environmental conditions to sustain crop production in midlatitude urban warehouse environments. This study was conducted to compare the environmental conditions, productivity, and water consumption for growing lettuce between GREENBOX and a conventional greenhouse that has been widely applied for crop production. Two modular GREENBOX units, equipped with LED lighting, hydroponic growing platform, and climate controls, were located in a high ceiling headhouse of a greenhouse complex to mimic warehouse conditions. We used bays in a nearby greenhouse that was glass glazed, equipped with supplemental lighting, and fully controlled by an Argus Titan control system for comparison purposes. Forty-eight (48) heads of Butterhead Rex lettuce (Lactuca sativa) were grown over four 30-day cycles in spring, summer, fall, and winter in the GREENBOX units and the greenhouse bays, respectively, at the University of Connecticut, Storrs, Connecticut, United States. Environmental variables, including light, temperature, relative humidity, and carbon dioxide concentration, were measured at a frequency of every minute. Biomass data of wet weight, dry weight, total leaf area, and lettuce head area were collected using destructive and non-destructive methods every three days. The water consumption rate was logged using a lysimeter. We derived the Daily Light Integral (DLI), Leaf Area Index (LAI), Specific Leaf Area (SLA), productivity, and water consumed per lettuce head, per unit wet weight, and per unit dry weight from the measurements. Results were analyzed using descriptive statistics and ANOVA. The DLI values in the GREENBOX units were significantly higher than the recommended minimum DLI by over 20 mol/m2.d in the GREENBOX units and over 10 mol/m2.d in the greenhouse bays. The range of the daily temperature variation is only a few degrees in the GREENBOX units, while in the greenhouse bays was over 20°C. The average daily temperature in both growing locations fell within the optimal range of 17-29°C for lettuce. The relative humidity inside both growing locations fell primarily within the optimal range of 40%-60%. The mean CO2 concentrations inside both growing locations were slightly lower than the ambient concentration of 350 ppm. Measured parameters such as LAI, SLA, and productivity followed similar patterns, slightly different amongst seasons and higher in warmer seasons. ANOVA revealed a slightly (statistically insignificant) higher level of productivity in the GREENBOX units over the greenhouse bays (p=0.16), with higher values during the warmer seasons (p=0.72 in spring and summer). GREENBOX used 1.83-2.69 L of water per lettuce head, while the greenhouse bays used 1.69-3.84 L of water per lettuce head year-round. The water use was consistently lower in the GREENBOX units. We found that the GREENBOX units and greenhouse bays provided comparable environmental conditions, biomass output, and water consumption. Those variables, however, were more consistent in the GREENBOX units. GREENBOX environment was less affected by outside weather and, therefore, exhibited reduced fluctuations. The GREENBOX is advantageous over the greenhouse as it does not require arable or open land for intercepting sunlight and can be operated in available urban buildings such as warehouses. Keywords: GREENBOX, Greenhouse, Lettuce, Productivity, Water use.