Root distribution of field-grown Chinese cabbage (Brassica campestris L.) under different fertilizer treatment

We determined the seasonal changes in the root system of field-grown Chinese cabbage under different fertilizer treatment (stripe, broadcast, and no-nitrogen application (absence of nitrogen)). Soil blocks less than 1 L volume were sampled from 1 quarter of a plant's rooting volume and roots were separated from the soil blocks by boiling. The root length was determined by the modified line intersect method. The fertilizer treatment did not affect substantially the root development. In deep soil layers, roots developed better in the broadcast plots than in the stripe plots in 1995, but the trend was not clear in 1996. With polyethylene mulch, the root length density of Chinese cabbage was the highest in the 0-10 cm soil layer and it decreased drastically below a 30 cm depth, due to the abrupt increase in soil hardness below this depth. The 0-30 cm layer accounted for more than 70% of the total root length. The root/shoot ratio for the nitrogen content was ca. 1.7%. Total root length ranged from 4,842 to 5,579 m plant(-1) at harvest (70 or 80 cm deep). The fine root length/weight ratio was 939 m g(-1) dry root and the fine root diameter averaged 92 muM. The differences in the strategy of root development in Chinese cabbage and crisp-head lettuce were discussed. Constraints on methodologies such as sampling depth, removal of debris, and saving of labor were discussed.