Production and quality of Sim carnations grown hydroponically in rockwool substrate with nutrient solutions containing different levels of calcium, potassium and ammonium-nitrogen

Abstract

The effects of 3 nutrient solution formulations on the production and quality of the Sim carnation varieties, Raggio d'Sole, White Sim, Manon and Doria grown in rockwool substrate were evaluated over 12 months in northern New South Wales. The solutions were: a standard (Std) formulation with a K:N ratio of 1.29:1.00, approximating that in mature carnations with N supplied as NO3-; the standard solution with 10% of the N as NH4+ (Std + NH4+); and a formulation with increased Ca and reduced K (High Ca). Production peaks occurred in March and October when the substrate was sampled for leachate nutrient composition and the flowers were assessed for quality. Total flower production from the Std + NH4+ (9.9/plant) and High Ca (9.7/plant) treatments exceeded (P<0.01) the Std solution (8.4/plant) from February to July while production from all treatments was similar (P>0.05) (mean of 10.3/plant) from August to December. Over February-December, production from the Std + NH4+ treatment (20.8/plant) exceeded (P<0.05) the other formulations. In excess of 75% of these flowers were first grade and the numbers of second and reject grades were not affected (P>0.05) by nutrient solution formulation. Stem diameter, stem strength and vase life were unaffected by nutrient formulation while flowers produced in March had thinner (3.11 v. 5.24 mm diameter) and weaker (139 v. 42 mm deflection from horizontal) stems than those produced in October. The pH in rockwool slabs was stable over time and compared to the standard treatment (7.17), it was lower (P<0.01) for the Std + NH4+ (6.13) and High Ca (6.76) treatments. The High Ca formulation increased Ca and reduced K concentrations in leaves, stems and flowers. Nutrient concentrations in youngest fully expanded leaves for all treatments were within the adequate range. The mean K: N ratio in mature carnations was 1.39:1.00 and this ratio with 10% of the N as NH4+ can be recommended in a nutrient formulation for commercial hydroponic carnation production in Australia.