The effect of spectral filters and nitrogen dose on the growth of chrysanthemum (Chrysanthemum morifolium Ramat., cv. Snowdon)

This study has searched for interactions between the effects of nitrogen do se, applied at one of four levels, 0.316, 1.0, 3.16 and 10 mM, and four dif ferent spectral filters on the growth and development of chrysanthemums. Th e filters used included two controls with different overall transmissions t o photosynthetically active radiation (PAR) and two further materials, whic h selectively filtered either red or far-red light, bur with PAR transmissi on similar to one of the controls. Increasing the nitrogen dose to a maximu m of 10 mM from the lowest level led to a four-fold increase in plant dry m ass, and a near two-fold increase in plant, height. The FR absorbing spectr al filters produced significantly shorter plants than both controls (by ca. 10% at final flowering) and for this variable there were no interactions w ith nitrogen dose. At 10 mM N, the FR-absorbing material also led to an inc rease in leaf area compared with the R-absorbing material (by 55% after 40 d). However, a significant interaction occurred with N dose, such that the FR-absorbing filter increased leaf area only at the highest levels of N. Th e results are discussed in terms of the potential use of spectral filters f or the control of the growth of ornamental crops.