This study investigated the effects of soil depths and soil organic fertilizer application on the growth characteristics of Spiraea bumalda ‘Gold Mound’ in a extensive green roof system. The treatments were 3 soil depths (10, 15 and 25 cm) and 5 soil types in mixture of artificial soil and organic fertilizer. We measured plant height, leaf width, leaf length, number of flowers, visual quality and survival rate from March to October in 2011. The growing medium of 10 cm soil depth showed the highest plant growth in A1 (amended soil 100%), and the lowest plant growth in O1A4 (organic fertilizer 20% + amended soil 80%) treatment. In case of 15 cm soil depth, Spiraea bumalda ‘Gold Mound’ showed a high leaf length and visual quality in O1A2(organic fertilizer 33% + amended soil 67%) treatment and high leaf width and number of flowers in O1 (organic fertilizer 100%) treatment. A1 treatment without organic fertilizer showed the lowest leaf length and poorest visual quality, and O1A4 treatment showed the lowest plant height and lowest number of flowers. At soil depth 25 cm, O1A1 (organic fertilizer 50% + amended soil 50%) treatment showed greater plant height, visual quality and number of flowers than other treatments. The leaf length and leaf width were more effective in O1 treatment. A1 treatment showed a relatively low leaf length, leaf width and visual quality. The higher the organic conditioner, the better the plant growth. And, survival rates of Spiraea bumalda ‘Gold Mound’ showed 92%, 88% and 76% at soil depths of 25 cm, 15 cm and 10 cm, respectively, in this a extensive green roof system. Therefore, the results showed that the growth of Spiraea bumalda ‘Gold Mound’ was affected by both soil quality and soil depth. Different optimal mixtures of organic fertilizer and amended soil were determined, depending upon soil depth.
For evaluating the effect of various organic fertilizer ratios on the Spiraea×bumalda ‘Gold Mound’ growth, a container green wall system experiment was conducted in a greenhouse at Konkuk university. The experimental planting grounds were prepared with different organic fertilizer ratios (A1L0, A8L1, A4L1 A2L1 and A1L1) and with drought tolerance and an ornamental value Spiraea×bumalda ‘Gold Mound’ was planted. The change in soil moisture contents, plant height, number of branches, number of dead leafs, number of leaf, number of shoots, length of node, length of leaf, width of leaf, root-collar caliper, chlorophyll contents and survival rate were investigated from April to Jun 2010.
1. The result of soil moisture contents was analyzed with weight unit in the container green wall system during the dry summer season. The soil moisture contents were significantly enhanced in the container green wall system in increasing order as the amount of fertilizer level increased A1L1> A2L1> A4L1> A8L1> A1L0 .
2. Compared to the control treatment (amended soil with 100% + organic fertilizer 0%) application, the highest plant growth was observed in the treatment of A2L1(amended soil with 67% + organic fertilizer 13%) application. However, the differences between the organic fertilizer ratio treatments of A1L1, A4L1, A8L1, and the A1L0 organic fertilizer application were mostly not significant.
3. The survival rate increased with the increasing application of organic fertilizer, but in the control treatment (amended soil with 100% + organic fertilizer 0%) application all the plants died.
Experimental results from the presented study clearly demonstrated that the organic fertilizer improved the survival rate more than the Spiraea×bumalda ‘Gold Mound’ growth at different levels of organic fertilizers. This strain can be utilized as a plant growth application in living wall systems during the dry summer season. Therefore, Spiraea×bumalda ‘Gold Mound’ is expected to be a highly valuable shrub for the green wall system if it should be considered in integration with stormwater retention or as a soil conditioner for increasing soil water contents in planting ground.