Facts and fables about trees and soil – test your knowledge!

For most people, the crown of the tree is what interests them most. However, we actually depend completely on the soil and what it brings us. The important thing in urban areas is to get as close as possible to imitating forest soil. The more natural the soil, the healthier the plant. This was stated by Pius Floris, special advisor and international consultant in Plant and Soil, during an internal knowledge session for employees of TFI Vitaler Groen. There is a lot of old knowledge about soil according to Pius, but there are also new insights about biological processes in soil on a regular basis. This knowledge session was valuable for us to both refresh and expand our knowledge – and may also interesting for you!

Test your knowledge using the following statements that were discussed during the knowledge session. Are they fact or fable?

Plant roots create their own acidity

Fact. Every tree has optimal growing conditions expressed as a minimum and a maximum pH value. It has recently been discovered that plant roots develop their own acidity and this varies from plant to plant. Therefore, it is important with any kind of soil cultivation or fertilisation to ensure that the pH value of the soil will not rise or decrease too much and that the type of fertilisation is adjusted for each plant. There are alternatives to fertilisation that are better suited to the plant’s natural habitat.

There are 20 important elements for essential life forms on earth

Fable. Soil analyses never examined more than 20 elements. This gave a distorted picture of certain soil treatments. The application of stone meal to fields is a good example. Stone meal always seemed to contribute little to nutrient-rich crops because little difference could be seen in the analyses. The reason is that not all elements were analysed. In fact, stone meal contains more than 60 elements. In the long run, stone meal stimulates soil life, builds up and stabilises organic matter in the soil and improves the natural resistance of plants. As a result, fewer fertilisers are needed in a field where stone meal has been applied, purely because stone meal provides a complete package of necessary elements for crop growth.

Calcium is important for plants to defend themselves

Fact. Calcium is the cement in cell walls. Calcium-deficient leaves have less cell strength, as the plant tissue is looser. The mineral is also important for the cell membranes. If there is too little calcium, the membrane starts leaking and anything can just enter the cell (source: wur.nl). So calcium is important for trees and plants to defend themselves, for example against lice. They poke into a plant an average of five times before deciding to move on. A leaf with strong cell stability is much harder for the aphid to prick than one with weak cell strength.

Raising soil around the tree is allowed up to 20 cm

Fable. Raising with soil around the tree is allowed up to a maximum of 5 to 10 cm. If there is too thick a layer of soil, it suffocates the soil. With a thin layer of extra soil, the soil-air exchange remains sufficiently intact and roots get enough oxygen.

Raising soil by littering around trees is possible

Fact. Raising soil can be done with a bedding layer. Why? A litter layer can be used well because it does not hinder soil diffusion. Moreover, a litter layer has many other functions that provide protection and enrichment of the soil.

1. A litter layer protects the soil from freezing temperatures in winter and drought in summer.
2. Litter forms a nutrient-rich humus layer that attracts earthworms, among others. They release nutrients from organic matter and improve the structure of the soil.
3. Many insects also hibernate in the litter layer, boosting biodiversity and the presence of natural enemies against pests.
4. In turn, the soil life and sheltering insects are food for many bird species.

The litter layer may be applied up to a maximum thickness of 7 to 10 cm. It will be fully absorbed into the soil in a few years and can then be replenished by 2 to 5 cm.

The intake capacity of mycorrhizal roots increases on average by 200%

Partly fable. It is not entirely true. A mycorrhizal root absorbs much more water and minerals, which is very decisive in drought. The absorption capacity increases by as much as 700% on average (source: phc.eu). As a result, plants absorb water and nutrients more easily and efficiently.

Mycorrhizae is the collective name for beneficial fungi that establish a relationship with the roots of trees and plants. In exchange for plant sugars from the roots, they make minerals and moisture absorbable for plants, keeping plants healthier and letting them use nutrition better. The roots of most plants are able to enter into symbiosis with mycorrhizae. It is the most common form of cooperation among plants and, for many species, indispensable for their survival. Read more about mycorrhizae here.