Impact of NH4+ : NO3- ratio and nitrogen supply on nitrogen remobilization in potted chrysanthemum grown in a subirrigation system

Subirrigation is being adopted as an environmentally friendly strategy for managing the nutrition of potted greenhouse plants. Here, we investigated two strategies for enhancing the remobilization of N during the development of the inflorescence in subirrigated potted chrysanthemum (Chrysanthemum morifolium Ramat.) in an attempt to improve nitrogen (N) use efficiency. (1) The replacement of a portion of the nitrate in the nutrient solution with ammonium decreased the nitrate content, especially in the stem plus petioles, and increased the reduced N content early in the growth cycle, but did not improve N use efficiency. (2) The use of a lower N supply (200 vs. 400 mg total N per pot delivered over 3 and 5 wk, respectively), either as nitrate or ammonium nitrate, eliminated nitrate accumulation prior to inflorescence development, thereby improving N use efficiency. Inflorescence quality was unaffected; however, at the lower N level there was some evidence of chlorosis on the oldest leaves. Thus, there may be considerable potential to reduce the N supply in a commercial greenhouse setting as long as an adequate supply is provided early in the growing period.