Chinese Cabbage (Brassica rapa L.) Parameters Describing Agronomic Performances of Fall and Summer Cabbage Ecotypes

Intercepted photosynthetically active radiation (IPAR) to biomass method is widely used in plant growth models to simulate biomass accumulation. This method is closely linked to radiation use efficiency (RUE), which can vary by species, cultivars, and location. Although Chinese cabbage (Brassica rapa L.) is a cool-season plant, it is cultivated year-round in South Korea. Therefore, investigating the RUEs of two different ecotypes of Chinese cabbage is crucial for developing accurate plant growth models. In this study, we examined RUEs and other key agronomic characteristics that influence Chinese cabbage growth across different growing seasons. Field studies were conducted to analyze the growth patterns of fall and summer ecotypes and to explore various agronomic traits for developing a leaf area index (LAI) model. Using a multivariate regression method, we developed an LAI model that simulates the leaf area index for both ecotypes across multiple locations in South Korea (R2 = 0.92). A total of 218 field data points collected from 35 sites between 2020 and 2023 were used to estimate the RUEs and LAIs of the fall and summer ecotypes. Results indicated that Chinese cabbage demonstrated more efficient photosynthesis in the fall, with RUEs of 2.3 g MJ−1 for the fall ecotype compared to 1.3 g MJ−1 for the summer ecotype based on regional estimation. This difference may be attributed to lower radiation availability per unit of heat growth during the summer season (0.3 MJ °C−1) compared to the fall (0.78 MJ °C−1). The findings of this study will aid plant modelers and enhance the accuracy of simulations for Chinese cabbage growth.