Strategic timing and rate of sulphur fertilization improves sulphur use efficiency in subirrigated greenhouse-grown chrysanthemums

Industry standards for nutrient delivery to greenhouse-grown ornamentals are typically in excess of the plant’s needs and can be reduced without causing adverse effects. Previous studies have reduced the level of specific nutrients or suite of nutrients over the entire crop cycle or at the onset of reproductive growth. Here, two split-plot experiments (four blocks each) were conducted with subirrigated, potted, disbudded chrysanthemums (Chrysanthemum morifolium Ramat.) grown under greenhouse conditions with sulphate treatment (2.25 mmol L-1 S supplied continuously over the crop cycle in experiment 2 only and 2.25, 1.125, or 0.5625 mmol L-1 S interrupted at inflorescence emergence) as the main plot and cultivar (‘Olympia’ and ‘Covington’) as the sub-plot. Morphological characteristics of plants with fully-expanded inflorescences were unaffected by decreasing S delivery over the crop cycle. Dry mass (DM) yields and S budgets revealed that supply-based S use and S uptake efficiencies increased markedly in both cultivars with decreasing S delivery. Minor amounts of reduced-S, rather than sulphate, were lost from leaves of ‘Covington’ during inflorescence development. High quality chrysanthemums had sufficient leaf-S (0.17%–0.23% DM) at inflorescence emergence even with the lowest S supply, which would deliver an approximate 87.5% reduction in S over the crop cycle compared with industry standards. The primary mechanism to obtain sufficient S for the growth of chrysanthemums in these studies was increased uptake efficiency.