Why is it crucial to analyse landscaping topsoil upon delivery to site?
Why analyse landscaping topsoil upon delivery to the site?
One element of my profession involves testing imported soil for its horticultural properties after delivery to site and prior to planting. It is highly recommended that clients test the soil before planting. Read further to understand the rationale behind this.
The primary reason is the uncertainty of the soil received. A test certificate does not guarantee that the soil matches the tested batch.
Another reason is the challenge of rectifying soil issues post-planting without harming the plants or causing delays.
What are imported soil blends?
Imported soil blends are a mix of mineral and organic materials, with blends typically containing 60-100% mineral content and 5-40% organics depending on the intended use. Various materials like compost, mulch, coir, sand, crushed sandstone, boiler ash etc are used in soil blends, each requiring testing due to their unique characteristics. The challenge lies in the variability of these ingredients, resulting from different originating sources, having differing characteristics.
For example, compost derived from felled fertilised trees could contain high phosphorus. Conversely, compost deriving from a native woodland is likely to have very low phosphorus levels. Boiler ash composition can vary from strongly alkaline to strongly acidic based on the source material.
Therefore, if raw ingredients are not continuously tested, the final blend may exhibit varying properties and provide extremely different results.
How can I be certain that the soil I receive matches the test certificate?
Imported topsoil often exhibits variation, leading to discrepancies between the delivered product and the results outlined in the test certificate. While these variances may often be insignificant, there are instances where they can have adverse effects. A physical change in the formulation may be observed to the eye however chemistry and nutrients can only be detected with laboratory analysis.
During a recent site inspection, a significant difference in organic matter was noted. One garden bed had around 70% organic matter, leading to issues like failing plants, slumping, odour, and lack of oxygen. In contrast, another garden bed had approximately 30% organic matter and the plants were growing well. In a separate incident, a topsoil labelled as "native" with supposed low phosphorus levels (<20 mg/kg) actually tested at 130 mg/kg, posing a serious risk to plant species sensitive to high phosphorus levels.
What's the key message?
The takeaway message is that the soil blend imported to your site may not represent the test certificate due to:
Variances in source ingredients
Differences in the volume proportion of inputs and final composition
To ensure accuracy, testing by a soil scientist or agronomist before planting is always advised for imported soil prior to planting.
Call The Urban Soil Doctor on 0473 505 550 before you import soil to your next project.
