Effects of Nitrogen and Potassium Rates on Yield of Summer Chinese Cabbage

Traditionally, P and K fertilizers are used as basal application to most crops, if not all. It is unclear what extra benefit would accrue when these two fertilizer are used in split applications at different growth stages of a crop. Thus, this study aimed to investigate the effect of split application of P and K along with N fertilizers on yield and quality of Chinese cabbage in Chongqing, China in 2011. There were six fertilizer treatments combining equal rates, but different timings, of N as urea, P as mono-potassium phosphate, and K as KCl at 300-90-150 kg N-P₂O₅-K₂O/ha. The six treatments included: (1) the conventional timing of fertilizer application (i.e. 100% of P and K fertilizers applied basally, N fertilizer split between basal and top dressing at rosette, cupping, and the fast growing stage; (2) N and P fertilizers split using the above mentioned stages and only K fertilizer was applied basally; (3) N and K fertilizers were split as above and only P fertilizer applied basally; (4-6) all N, P, and K fertilizers were split in above mentioned stages, but with three different allocation percentages.

Results showed that at the same N, P, and K fertilizer rates, the conventional timing of fertilizer application produced the least cabbage yield, while the treatment splitting N, P, and K fertilizers basally at 20% N, 30% P₂O₅, 30% K₂O, and topdressing only at rosette stage at 40% N 40%, 30% P₂O₅, 30% K₂O and cupping stage at 40% N, 40% P₂O₅, 40% K₂O produced significantly higher yield than the other treatments. All the other treatments had the similar yield level with non-significant differences. Further, all the splitting treatments enhanced quality parameters by 2 to 5% for vitamin C, 13 to 33% for reducing sugar, 3 to 28% for amino acids, and 0 to 26 % of reduction for nitrate N compared to the conventional timing of fertilization. The highest yield treatment also improved the cabbage quality by enhancing contents of vitamin C and reducing nitrate N in the leaf head, slightly decreasing reducing sugar and amino acids compared to the other splitting treatments. Chongqing-BFDP-11-01