Changes in Leaf and Growth of Pak Choi in a Semi-closed Greenhouse in Eastern China

To study and model changes in the development of pak choi (Brassica rapa ssp. chinensis Makino), three pak choi cultivars—Xinxiaqing No. 5 (Xinxiaqing 5), Haiqing, and Huawang—were grown in a modern greenhouse. Four structural parameters, including leaf length, leaf width, and plant height and width, were measured regularly every 3 days. The results showed that the changes in plant height and width, and leaf length and width of the three cultivars followed sigmoidal trends. Logistical regression models {Y = K/[1 + (K – L0)/L0 × exp(–r × t)]; Y = K/[1 + (K – L0)/L0 × exp(−r × rad)]} of the leaf length and width accumulated with growth days and with accumulated radiation fit the actual data very well, with the correlation coefficient R2 all greater than 0.98. The R2 values of the plant width accumulation models were all greater than 0.93, whereas the R2 values of the plant height regression models were not robust. In this study, the regression models of changes in plant height and width, and leaf length and width of pak choi were used to study the changes of morphological characteristics and analyze the change rules of pak choi growth and development.