The 2009 ASHS Annual Conference

Optimal moisture content for growth is specific to cultivar and growing media. Studies of physiological and growth response as well as substrate behaviour under different irrigation regimes are essential to the future development of automated irrigation technology. A greenhouse study was conducted in the Fall of 2008 to quantify growth and physiological responses of potted Chrysanthemum morifolium (aka Dendranthema grandiflora Ramat.) under five different irrigation programs. Five cuttings per 6-inch pot were grown in a 70:30 peat-coir mix. Treatments were imposed by irrigating plants to saturation, using a zero runoff sub-irrigation system, with successive irrigation events triggered as substrates reached 40, 30, 20, 15 and 12% volumetric moisture content minimums. Harvests were conducted at 2-week intervals to determine fresh and dry weights. Leaf stomatal conductance (gs) and photosynthetic rate were measured at the end of weeks 9 and 11 to evaluate treatment effects at growth progression intervals and throughout week 12 to evaluate long-term effects on carbon fixation. Lower gs occurred in the drier treatments (12 and 15%) at week 11, with no differences in week 9. A 6-day trial conducted during week 12, revealed declines in gs as treatment minimums were approached. Chlorophyll fluorescence was measured at 2-week intervals to estimate possible damage to photosynthetic apparatus as a consequence of water stress. Substrate analysis revealed air-filled porosity of 13.9% and an oxygen diffusion rate of 140 x10-8 g O2 cm-2 min-1 at container capacity of 78%. Oxygen content in the substrate was monitored during week 13 to evaluate treatment effect on root zone oxygen levels. Electrical conductivity and pH of substrate effluent were also measured during harvests. Optimizing irrigation management that is specific to both cultivar and substrate could increase the amount of biomass produced per liter of transpired water, thus reducing irrigation inputs during crop production.