Singapore’s green environment: Don’t forget quality of the soil, too

Our nation’s emphasis on tree planting has resulted in a green environment around our island that few nations can boast of. While great work has been done, to truly reach the next level, our approach must be thoughtful and sustainable.

The Government could shift part of its focus to something equally important: The soil beneath the greenery. Our objective should be to improve soil structure by increasing the organic matter in the soil.

Improved soil allows rainwater to enter more easily, alleviating surface run-off and flooding. Organic matter stabilises the soil, reducing erosion. This decreases the silt in drains, canals and, ultimately, our reservoirs, saving costs on dredging and filtration. The soil can then serve as a source of carbon sequestration, or storage.

To do this, I suggest the National Parks Board establish a two-step programme. First, build up soil organic matter using suitable understory plants. Second, promote research and development of biochar as a soil amendment.

Suitable plants bordering trees and roadside greenery can be used to trap leaves and twigs. As they decompose, soil structure will improve.

Experiments can be started by planting Singapore daisy (Sphagneticola trilobata) and vetiver grass (Chrysopogon zizanioides) around existing rain trees (Samanea saman). Within the thick plant border, dried leaves will form a protective layer on top of the soil (akin to the piles of leaves under trees in the Botanic Gardens). These small leaves do not collect water, thus no mosquitoes can breed.

The next step involves using biochar to stabilise carbon in the soil, imitating the Amazon’s terra preta (“black earth”) where the carbon in the man-made soil has been stable for thousands of years. The carbon in biochar is resistant to decomposition, enabling long-term carbon sequestration in tropical soils.

The Government should research how to start a pyrolysis facility that creates biochar using the leaves and branches from tree trimmings. They can then scatter biochar on green areas around Singapore, as they already do with compost created from existing facilities.

The knowledge and technology can then be promoted internationally to other tropical nations.

If these two steps are implemented, Singapore could relieve flooding and soil erosion while fighting climate change. Local jobs and industries will also be created.