Evaluating Labor Productivity in a Plant Production System with Sole-source Lighting: A Case Study

Abstract

Labor productivity in terms of material value (weight of plants harvested per hour per person) was evaluated for 6 months from the start of operations in a research facility at Osaka Prefecture University (Osaka, Japan), serving as a model system for plant production with sole-source lighting (also referred to as a “vertical farm” or “plant factory”). The research facility is capable of producing lettuce plants (Lactuca sativa) at a maximum production rate of ≈5000 plants/day when the relative harvest rate (i.e., number of plants harvested/maximum potential number of plants harvested) is 100%. However, in the present study, the relative harvest rate at the research facility was in the range of 17% to 65% and labor productivity varied from 1.5 to 6.0 kg·h−1 per person. The evaluation results indicated that increasing the weight of plants harvested and increasing the relative harvest rate was necessary to maintain a high level of labor productivity. The processing time for harvesting was greatest among all plant operations, suggesting the need to reduce the time taken in this operation to increase the labor productivity in the research facility and in other plant production systems with sole-source lighting (PPSLs). This study demonstrates the importance of analyzing labor productivity for increasing the commercial feasibility of PPSLs. However, further long-term investigation with higher relative harvest rates is required for a more definitive conclusion.