Objective  To make clear morphological symptoms of potassium (K) deficiency in banana seedlings, discuss the effects of K deficiency and K resupply on growth and nitrogen (N), phosphorous (P), K balance of banana seedlings and provide a basis for nutrition diagnosis and blanced fertilization of banana seedlings.

Method  Through quartz sand culture experiment, complete nutrient solution cultivation was marked as the control treatment to observe morphological characteristics and appearance time of K-deficient symptoms. K deficiency and K deficiency-resupply treatments were conducted to study the changes of biomass, root morphological parameters and N, P, K uptake of banana seedlings.

Result  The K-deficient symptoms were old leaves chlorosis, successive orange-yellowing of main veins and margins of middle leaves, small oval spots in leaf margins and reddish brown petioles. When the seedlings were in severe K deficiency, mesophylls near the veins of orange-yellow leaves were blackening and dried to death, the dead leaves were brown, fully expanding new leaves were not erect, and the upper leaves were soft and drooping. K deficiency significantly inhibited the growth of banana seedlings. Compared with CK, the biomass of shoots and roots in K deficiency treatment decreased by 31% and 39% respectively, the length, surface area and volume of roots decreased by 30%, 31% and 34% respectively, and the decrease ranges of fine roots were more than that of middle roots. K deficiency also changed N, P, K balance of banana seedlings. Compared with CK, N contents of shoots, roots and whole plants in K-deficient treatment increased by 19%, 21% and 19% respectively, P contents increased by 40%, 12% and 38% respectively, K contents decreased by 73%, 56% and 72% respectively, N and K uptake decreased, P uptake of roots decreased, N/K and P/K ratios in shoots, roots and whole plants increased significantly, N/P ratio in shoots and whole plants decreased significantly, and N/P ratio in roots increased significantly. After resupplying K in K deficiency treatment, the K-deficient morphological symptoms of banana seedlings disappeared, but the biomass, N, P and K contents and uptakes of banana seedlings could not recover simultaneously. The biomass of banana seedlings was still lower than that of CK, and N contents of shoots, roots and whole plants and P, K contents of roots were higher than those of CK. K contents and uptakes of shoots and whole plants did not increase to normal levels. P uptakes of shoots and whole plants decreased significantly and was lower than that of CK.

Conclusion  The effects of K deficiency on nutrition status of banana seedlings are significantly greater than that of phenotypic characteristics, and the recovery of nutrition status lags behind phenotypic characters. Banana seedling fertilization should apply to its nutritional characteristics.