Evaluation of alternative methods of applying sulfur fertilizers to chrysanthemums

Previous research has shown that supplying adequate sulfur (S) continuously in combination with reduced amounts of nitrogen (N) will produce a quality plant. However, not all commercially available fertilizers use the same source of S, contain the same or optimal concentration of it, or contain any S at all. Additionally, nutrient incompatibility can occur if all the macronutrients are combined in one solution or one dry fertilizer. Thus, the objective of this research was to determine the effect of different methods of application and different types of S fertilizers on chrysanthemum growth. Two experiments were conducted in which three S sources (H2SO4 , MgSO4 , and K2SO4) were applied in combination with three N concentrations (50, 100, and 150 mg L-1 ) as fertilizer treatments. Sulfur was applied at 10 mg L-1, either continuously-by slightly acidulating the fertilizer solution with H2SO4-or in one, two, or three single, discrete applications as either K2SO4 or MgSO4 . Leaf N concentration was greatest when 100 or 150 mg N L-1 was applied. As expected, S applied continuously by slightly acidulating the fertilizer solution with sulfuric acid resulted in higher leaf S concentration and larger flower diameter than under any of the other treatments. Together, plants fertilized with S continuously at 10 mg S L-1 and N at 100 mg L-1 were the largest, had the largest flower diameter, and contained the greatest leaf N and S concentrations. Sulfur concentration in the mix was highest and N concentration lowest when S was supplied continuously. Thus, if growers need to supply S and acidulate their water, sulfuric acid would be the best choice. If there are concerns about possible S contamination in landfills or in mix recycling, either potassium or magnesium S, applied multiple times as single applications in combination with 100 or 150 mg N L-1 , may be a better choice.