Estimation of leaf number and leaf area of hydroponic pak-choi plants (<Emphasis Type="Italic">Brassica campestns</Emphasis> ssp,<Emphasis Type="Italic">chinensis</Emphasis>) using growing degree-days

Temperature is a principal environmental factor that directly affects the growth and timing of appearance for crop leaves. To estimate the leaf number and leaf area of ‘Seoul’ pak-choi plants (Brassica campestns ssp.chinensis), we applied the concept of growing degree-days GDD=(T_avg-T_base) × days, where T_avg, T_base and days were the daily average air temperature, base temperature, and days after transplanting, respectively. Leaves that were beginning to unfold with a leaf area ≥1 cm₂ were counted every 2 to 3 d. Linear relationships were found between leaf number and days after transplanting as well as between leaf number and GDD. The rate of appearance and the number of leaves per GDD were 0.542 leaves d^-1 and 0.051 leaves oC^-1 d^-1, respectively. In contrast, the relationship was non-linear between leaf number and leaf area, with the latter being calculated as (128.9+11.6×GDD-0.03×GDD²)/1+(0.051×GDD+3.5) /13.7)^-3.9] (cm₂oC¹ d^-1). Using model validation, we found that the estimated leaf number and leaf area showed strong agreement with measured values. our results demonstrate the usefulness of modeling to estimate total leaf area and growth from hydroponically grown pak-choi plants.