Nutrient management for cabbage

The objectives of the 2014 project were to determine the optimal N and K rates for fall Chinese cabbage in comparison with the summer variety tested in 2013. The experiment consisted of six treatments including two N rates (300 and 375 kg N/ha), one P rate (90 kg/ha) and four K rates (0, 75, 150, and 225 kg K₂O/ha). Nitrogen and K fertilizers were split three times between a basal application at seeding (30%), and topdressing at seedling (30%) and rosette stages (40%). Fertilizer P was applied once at seeding.

In 2013, summer cabbage yield at each N rate increased significantly with increased K application without leveling-off. In 2014, however, fall cabbage yield was significantly enhanced by K application at the low N rate, but not at the high N rate. With application of 225 kg K₂O/ha, the cabbage yields reached 44 t/ha at 300 kg N/ha and reached a maximum of 46 t/ha at 375 kg N/ha. These yields were 5.8 t (15%) and 7.3 t (19%) more than the K omission treatment. In terms of cabbage quality, the content of vitamin C, amino acids and soluble sugar in the low N rate treatments increased with K application and leveled off at 150 kg K₂O/ha. At the high N rate, however, these three quality traits were further improved and then dropped as K rate rose further. The concentration of N, P and K in leaves reached a maximum at 21 days after the first topdressing and then decreased with time, indicating that three weeks after topdressing may be the suitable time interval for the next fertilization during the fast-growing period of the fall Chinese cabbage in the region.