Effect of NH_4~+-N/NO_3~--N Ratios on Growth and Some Physiological Parameters of Chinese Cabbage Cultivars

The responses of three cultivars of Chinese cabbage (Brassica chmensis L.), one of the main vegetable crops in China, to different ratios of NH4+-N/NO3--N was investigated to find the optimal ratio of ammonium to nitrate for maximal growth and to explore ways of decreasing the nitrate content, increasing nitrogen use efficiency of Chinese cabbage, and determining distributions of nitrogen and carbon. Three cultivars of Chinese cabbage were hydroponically grown with three different NH4+-N/NO3--N ratios (0:100, 25:75 and 50:50). The optimal ratio of NH4+-N/NO3- -N for maximal growth of Chinese cabbage was 25:75. The increase in the ratio of NH4+-N/NO3--N significantly decreased nitrate content in various tissues of Chinese cabbage in the order of petiole leaf blade root. The highest total nitrogen (N) content was found when the ratio of NH4+-N/NO3--N was 25:75, and N contents in plant tissues were significantly different, mostly being in the order of leaf blade petiole root. At the NH4+-N/NO4+-N ratio of 25:75, the biomasses of Chinese cabbage cultivars 'Shanghaiqing', 'Liangbaiye 1' and 'Kangre 605' increased by 47%, 14% and 27%, respectively. The biomass, SPAD chlorophyll meter readings and carbon content of 'Shanghaiqing' were all higher than those of 'Liangbaiye 1', while nitrate and total nitrogen contents were lower. Thus, partial replacement of nitrate by ammonium could improve vegetable production by both increasing yields and decreasing nitrate content of the plants.