Possibilities for Soilless Cultivation in Cut Chrysanthemum: Effect of Irrigation Frequencies and Spacing Schedules

Three levels of irrigation frequencies, provided by root misting, combined with three plant densities and two spacing treatments were tested to evaluate the optimum conditions during the first crop stages of chrysanthemum in a soilless cultivation system (aeroponics) in an experiment conducted in autumn. The optimum misting frequency was 32’ times  min h. A higher frequency (121’) had no additional effect, whereas the lowest frequency (16’) had a negative effect on total shoot dry mass (TDMs). The highest plant densities (172 and 344 plants m) could be used until week 2 with hardly any negative effect on TDMs, and resulted in higher light interception and higher total shoot dry mass per m. During the period between week 2 and 4 after planting, a higher density (172 compared to 86 plants m) had a strong negative impact on the TDMs, while a further increase to 344 plants m had only a minor effect. When spacing (week 2) from 344 to 172 plants m, TDMs at week 4 was not negatively affected by the high starting density, though spacing from 172 to 86 plants m resulted in a 13% reduced TDMs, as compared to plants grown at 86 plants m continuously. It is concluded that the irrigation frequency until week 4 after planting under these light conditions, should be three times per hour. Furthermore, very high plant densities (e.g., 344 plants m) are feasible until week 2 with hardly any negative effects on plant growth, while spacing schemes give several possibilities for a smaller reduction of the TDMs, than that expected by the higher initial densities. INTRODUCTION Most single-harvest greenhouse crops with a short production cycle and a high plant density, e.g., chrysanthemum, are still predominantly grown in soil. Cut chrysanthemum represents one of the most intensive cropping systems in horticulture, with approximately four to five successive crops per unit area annually. Since long, research has focused on development of cost-effective systems to achieve reductions in the environmental impact and improvements in production efficiencies of such intensive cropping systems (Costa and Heuvelink, 2003). Soilless cultivation systems are often used in horticulture because of their high production potential, independence from soil conditions and soil-borne diseases, as well as the possibility of drainage recirculation, which results to reduction of environmental pollution by emission of fertilizers and crop protectants (Costa and Heuvelink, 2003). Furthermore, we expect that by implementing mobile cultivation systems, the manipulation of plant density in different developmental stages of a crop becomes possible. A successful attempt was made with an almost completely hydroponic ebb-andflow system, where the substrate (jute plugs) was merely used as support material, and a separate rooting phase was utilized (Buwalda et al., 1994; Buwalda and Kim, 1994). These experiments showed for the first time that production was possible for 10 consecutive chrysanthemum crops almost without substrate. This raises the question if substrate is really necessary, even as support material, and whether it is possible to a [email protected] Proc. IS on High Technology for Greenhouse Systems GreenSys2009