An experimental study on GREENBOX technology: feasibility and performance

Abstract. Worldwide population increase and urbanization have created significant challenges to food security and safety. We have developed the GREENBOX technology, allowing growing plants in individually climate-controlled boxes in urban warehouse environments. Each GREENBOX consists of a thermally insulated modular structure with an artificial lighting source, hydroponic nutrient supply system, and environmental controls. We constructed two GREENBOXES and grew Butterhead Rex lettuce (Lactuca sativa) over a 30-day growing cycle for four seasons and quantified crop growth with biomass data (wet weight, dry weight, total leaf area, and lettuce head area). Environmental data (light, temperature, relative humidity, and carbon dioxide) were collected. A lysimeter was used to determine the water consumption rate by plants. We used descriptive statistics to analyze the results. Data collected indicates that GREENBOXES provided the desired environmental conditions for growing the crops all year. The Daily Light Integral (DLI) in the GREENBOX ranged between 32.48-37.23 mol/m2.d at the lettuce heads' height and were regulated at the grower's discretion. The mean temperatures inside were around 24.5-26.99°C, falling within the optimal range (17-29°C).  The average relative humidity all year falls within the ideal range of 40-60%. The CO2 concentration inside the boxes fell slightly below the ambient concentration of 350 ppm, averaged 300-320 ppm in different seasons. Lettuce plants were all healthy and growing to full size in the 30-day cycle, regardless of seasons. Measured parameters such as Leaf Area Index (LAI), Specific Leaf Area (SLA), and productivity followed similar patterns, slightly different amongst seasons and higher in warmer seasons. GREENBOX uses around half a gallon per head of lettuce consistently. Our results indicate that the GREENBOX technology has a high potential to be scaled up for food production in mid-latitude urban environments.