The effects of biochar amendment and companion planting with Sedum on water holding capacity and the health conditions of the plants for green roofs

Abstract

Extensive green roofs have benefits of weight and cost reduction for the buildings, though their shallower substrates resulted in fewer options of plant species to introduce and lower water holding capacity. Although previous studies reported that companion planting with Sedums and biochar amendment can improve soil water content, their synergistic effects were not fully clarified. Therefore, this study aimed to reveal the effects of the combination of companion planting with Sedums and biochar amendment on the health conditions of the plants. We cultivated two plant species for green roofs (Mimosa pudica and Rosmarinus officinalis) with/without Sedum album in a greenhouse under drought condition for 16 days. Additionally, we added biochar at rates of 0, 15, 30 and 60％ by volume to the substrates. The results indicated that there were no significant synergistic effects by the combination between soil water content and water holding capacity. However, the health conditions of plants were healthy when biochar was added and/or Sedums were planted together. Additionally, water holding capacity was improved with the increase of biochar application rate. In conclusion, we revealed that although synergistic effects between companion planting with Sedums and biochar amendment would not be induced on green roofs, the effects of biochar amendment can improve water holding capacity without wilting of the plants.