Sulfur Requirements of Container - grown Pin Oak and Japanese Maple by Jake Forrest Browder

Substrates of container-grown plants are commonly pre-plant amended with sulfated micronutrients to supply micronutrients. However, the cause for the resulting increase in growth may be due to micronutrient addition or to other factors, such as S addition or substrate acidification. Container-grown pin oak (Quercus palustris Münchh) and Japanese maple (Acer palmatum Thunb.) seedlings were grown in a 100% pine bark substrate and amended (or not) with one of the following treatments: control (no amendment), Micromax, K2SO4, H2SO4, HCl, chelated micronutrients, elemental S, or CaSO4. After 11 weeks, dry weights of plants in all treatments supplying S were higher than plants receiving no S. Dry weights of plants in all experiments receiving the chelate treatment were not higher than dry weights for control plants. These data indicated that S, not micronutrient application, was a primary cause of increased growth from the addition of sulfated micronutrients. However, at substrate pH 5.4 dry weight of plants fertilized with Micromax was higher than dry weight of plants fertilized with FeSO4. At a substrate pH of 4.1 there was no difference in dry weight between the Micromax and FeSO4 treatments. Thus, there are conditions such as higher substrate solution pH (5.4 vs. 4.1), where Micromax may prove advantageous over sulfur alone since it would supply micronutrients as well as S.