Alleviating Effect of the Application of the Easily Decomposable Carbohydrate on Ammonium Toxicity in Chinese Cabbage (Brassica rapa var. chinensis)

Abstract

An excess application of N fertilizer causes physiological and morphological disorder known as ammonium(NH₄ + ) toxicity in Chinese cabbage and it has been to be an issue for appropriate N fertilizer management. Hence, the pot experiment was conducted in order to evaluate the alleviating effect of the application of the easily decomposable carbohydrate on NH₄ + toxicity in Chinese cabbage. Four levels of urea at 0, 160, 320, and 640 kg N ha -1 , represented as T1, T2, T3, and T4, respectively, were applied. In order to evaluate the alleviating effect of the application of the easily decomposable carbohydrate (sucrose) at T3 and T4 where NH₄ + toxicity had occurred, five levels of sucrose were applied to meet C/N ratios of 0, 2, 4, 6, and 10, respectively. Our results showed that the NH4+ toxicity was observed at T3 and T4 at 5 days after treatment(DAT). NH4+ toxicity contributed to decrease fresh weight, length of leaves, length of root, and number of leaves significantly (p + toxicity had a good performance at T3 with the alleviating effect as 73 % and reduced in NH₄ + -N content in soil at 29 DAT. In the maximum N rate of T4, however, sucrose application recovered it as 32 % only compared to T2 even though the same C/N ratio was treated. Consequently, sucrose as the easily decomposable carbohydrate played crucial role to reduce NH₄ + concentration in soil and finally alleviated NH₄ + toxicity in plant.