Development of Planting-density Growth Harvest (PGH) Charts for Quinoa (Chenopodium quinoa Willd.) and Sowthistle (Ixeris dentata Nakai) Grown Hydroponically in Closed-type Plant Production Systems

When designing a plant production system, it is crucial to perform advanced estimation of growth and productivity in relation to cultivation factors. In this study, we developed Planting-density Growth Harvest (PGH) charts to facilitate the estimation of crop growth and harvest factors such as growth rate, relative growth rate, shoot fresh weight, harvesting time, marketable rate, and marketable yield for quinoa (Chenopodium quinoa Willd.) and sowthistle (Ixeris dentata Nakai). The plants were grown in a nutrient film technique (NFT) system in a closed-type plant factory under fluorescent lamps with three-band radiation under a light intensity of $140{\mu}mol{\cdot}m^{-2}{\cdot}s^{-1}$, with a 12-h/12-h (day/night) photoperiod. We analyzed the growth and yield of quinoa and sowthistle grown in nutrient solution at EC $2.0dS{\cdot}m^{-1}$ under four planting densities: 15 cm between rows with a within-row distance of $15{\times}10cm$ ($67plants/m^2$), $15{\times}15cm$ ($44plants/m^2$), $15{\times}20cm$ ($33plants/m^2$), and $15{\times}25cm$ ($27plants/m^2$). Crop growth rate, relative growth rate, and lost time were closely correlated with planting density. We constructed PGH charts based on the growth data and existing models. Using these charts, growth factors could easily be determined, including growth rate, relative growth rate, and lost time, as well as harvest factors such as shoot fresh weight, marketable yield per area, and harvesting time, based on at least two parameters, for instance, planting density and shoot fresh weight.