ABSTRACT
Biochar is the product of thermal degradation of organic materials in the absence of air (pyrolysis) and is distinguished from charcoal by its use as a soil amendment. In recent years biochar has shown its potentiality for restoration of infertile soils because of its high affinity for nutrients and long persistence. However, the majority of the work is confined to agricultural soils and, to date, very few studies have examined biochar’s impacts on urban horticulture. Therefore a short-term experiment was conducted at an urban park in northern Singapore to determine (1) the effects of biochar, alone, or in combination with other organic (compost) amendment on urban soils, and (2) a comparison between charcoal, biochar and inorganic fertilizer on urban soils and plant growth. Biochar was mixed with loamy soil in different proportions, and a perennial herb commonly grown as ground cover (Dissotisrotundifolia) was planted with the following treatment combinations: without amendment (control, T1), soil + compost (3:2, T2), soil + compost + biochar (3:2:1, T3), soil + biochar (2:1, T4), soil + fertilizer (T5), soil + compost + charcoal (T6) and soil charcoal (2:1, T7). The results demonstrated that the application of char materials, particularly biochar, resulted in significant improvements in urban soil quality and can be recommended as a potential soil amendment for growing perennial ground cover in the tropical environment of Singapore. Although plant physiological characteristics did not show any significant differences, results from the soil analysis showed positive responses following the addition of biochar, alone or in combination with compost. Significant increases in soil nutrient status and organic matter content were observed from the organic amendments, but these increases were more significant where biochar was a component of the amendment.
