Soil yourself
The debate over whether to build a housing development or maintain prime ag land in ‘Ewa has divided communities, politicians and even farmers. No one can seem to agree on the land's actual value one way or another. Turns out the soil type itself can shed some light on which direction is better (and safer) for us all.
This week I’m harvesting soil from a red worm composting bin for a DIY story in INhonolulu Magazine. The excreted organic matter these wriggly invertebrates deposit into the soil enriches it with high concentrations of nitrogen, phosphates and potassium. The worms also aerate the soil simply by crawling through it and help mix organic material from the top of the compost into the bottom of the bin.
Soils in general provide several key services that make life, as we know it, possible:
It’s a medium for plant growth.
It stores and purifies water.
It’s a habitat for organisms like bacteria and earthworms that cycle nutrients for plants.
It recycles and composts organic material.
It’s a medium for building and engineering.
All this thought about soil got me wondering about the fertile vertisol soil that predominantly comprises the ‘ewa plain. There are many different kinds of soil throughout the state and some are better than others at providing those five services. On the island of O‘ahu alone, there are nine of the 12 major soil types in the world, most of which would be better choices for building on than the ‘ewa vertisol.
“Vertisols are quite unusual soils,” says Dr. Jonathan Deenik of UH Manoa’s Department of Tropical Plant and Soil Sciences about the ‘ewa plain soils. “They’re the primary soil type in the ‘ewa plain and the waianae coast. We know [humans] have been producing food on those lands for a long time. In terms of agriculture, it’s some of the best soil in our State.”
Vertisol soils however, by their very nature, are bad for building stable structures. Vertisol is mostly comprised of clay that swells up when it’s wet and cracks when it dries.
“Vertisol is not a stable soil type. If it’s cracking, it’s moving,” says Deenik. “This is a defining property of this soil type and needs to be taken into account if you’re going to try and build here. If you haven’t taken into account the engineering property of that soil, all those houses are going to fall down.”
Developers planning to build on the ‘ewa plain would likely have to excavate and replace the vertisol with something like crushed coral which they would pack down into a stable foundation to build on. No amount of earthworms would be able to bring prime ag soil back at that point. Excavating the plain would render the land agriculturally useless for tens of thousands of years. Once that soil is gone it’ll be gone (effectively) forever.
Is that really the legacy we want for the ‘ewa plain?