Impact of various combinations of nitrate and chloride on nitrogen remobilization in potted chrysanthemum grown in a subirrigation system

Subirrigation is gaining popularity as an environmentally friendly strategy for managing the nutrition of potted chrysanthemum (Chrysanthemum morifolium Ramat.), as well as many other popular potted ornamental crops grown in the greenhouse. Subirrigation systems recycle the nutrient solution, but unlike the common practice of overhead irrigation, salts are more likely to accumulate in the top of the growing medium. Thus, further research is required to optimize the technology for the timing and application rates of soluble nitrogen in order to benefit from the high mobility of this nutrient within plants. This study tested the hypothesis that N use efficiency of subirrigated potted chrysanthemum can be improved by managing the nitrate status of the plant. Replacement of the nitrate supply with water 1 wk prior to inflorescence emergence (the midpoint of the experimental 10-wk crop cycle) was more effective in reducing the nitrate contents of above-ground tissues, particularly the stems and petioles, than the use of nitrate or various combinations of nitrate and chloride, thereby resulting in an improved N usage index (i.e., shoot dry mass X (shoot dry mass/shoot N content)). Shoot or inflorescence dry mass and N content were unaffected at the conclusion of the crop cycle by this treatment, whereas the electrical conductivity of the pot medium was reduced. Thus, elimination of nitrate prior to inflorescence emergence can be an effective strategy for improving N use efficiency in subirrigated potted chrysanthemums without sacrificing quality.