GREENBOX Technology I - Technical Feasibility and Performance in Warehouse Environment

Abstract

Highlights There are pressures on food security due to increasing population, demand, and urbanization. GREENBOX uses controlled environment agriculture for urban crop production in warehouse settings. GREENBOX provided the required environmental conditions and comparable biomass output year-round. GREENBOX is technically feasible for urban crop production. Abstract. The surging worldwide population and urbanization have increased food security and safety pressures. Therefore, there is a need to increase food production capacity in urban areas to feed this growing population. We have developed the GREENBOX technology to grow vegetables in individual climate-controlled boxes in urban warehouse environments. A GREENBOX is a thermally insulated modular structure of standard size with an artificial lighting source, a hydroponic nutrient supply system, and environmental controls. GREENBOX units can be used together in various numbers to form different configurations and production capacities. This study was conducted to evaluate the technical feasibility and performance of the GREENBOX technology for urban crop production in warehouse settings commonly found in urban areas. Two model GREENBOX units, constructed with commercially available parts, were located in a high-ceiling headhouse of a laboratory greenhouse complex at Storrs, Connecticut, USA, for the study. Forty-eight (48) heads of Butterhead Rex lettuce (Lactuca sativa) were grown in the model GREENBOX units (24 in each) over a 30-day growing cycle for four seasons. Environmental data, including light, temperature, relative humidity, and carbon dioxide, were collected using iPonic sensors at a frequency of every minute and processed to 15-minute averages. Crop growth was quantified with biomass data, which were wet weight, dry weight, total leaf area, and lettuce head area, using destructive and non-destructive methods every three days. A lysimeter was used to determine the water consumption rate by plants every fifteen minutes. 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. Descriptive statistics were used to describe and analyze the results. The DLI in the GREENBOX ranged between 32.48-37.23 mol/m2.d at the lettuce heads' height, higher than the recommended minimum DLI of 6.5-9.7 mol/m2.d. GREENBOX does not rely on external light but solely on the artificial lighting source, regulated at the grower's discretion. The mean temperatures inside were 24.5-26.9°C, falling within the optimal range of 17-29°C for lettuce. The artificial lighting source was a heat source to sustain cultivation. All year, the average relative humidity was 35.53%-58.54%, mostly within the ideal range of 40%-60%. The CO2 concentration inside the boxes fell slightly below the ambient concentration of 350 ppm, between 301.39 and 311.34 ppm over different seasons. Measured growth parameters, including LAI (5.3-6.5 cm2/cm2), SLA (344.3-569.3 cm2/g), and productivity (6.33-7.38 kg/m2), all followed similar patterns, slightly different amongst seasons and higher in warmer seasons. GREENBOX used 1.83-2.69 liters of water per head of lettuce consistently year-round, 95% lower than soil-based irrigation. Lettuce plants were healthy and grew to full size in the 30-day cycle, regardless of the season. Our study showed that the GREENBOX technology was capable of providing desired environmental conditions for growing lettuce crops all year around in the experimental warehouse structure and consequently having a high potential to be applied in food production in mid-latitude urban settings. Keywords: Agricultural facility, Environmental control, GREENBOX, Lettuce, Urban agriculture.