|MadSci Network: Agricultural Sciences|
Tyres are being used more and more for vegetable gardens. In cold climates the black of the rubber helps warm up the ground inside the tyre which helps promote root growth, so tyres there are left black. Potatoes especially benefit from the tyres.
You are mostly correct about their usefulness in reducing water use. Actually the water use in the warmer soil inside the tyre will be greater, but in comparing the amount of water one puts into several tyres and the the amount of water one would normally add to an equivalent garden space, you would find that much less goes to waste (evapoation, weeds, runoff, etc.). I am thinking in Barbados, the reason people paint the tyres white, is that because of the heat of the country and it's soils an increase in soil temperature is probably a bad thing. Black tyres in that environment would cook the roots unless lots of water was applied. Touch a white tyre and a black tyre that are in full sun at mid-day. There will be a tremendous difference. The white colour is very good at reflecting away the light so the tyre will be much cooler.
As for insect repelling. I talked with an entomologist friend (Dr. Scott Hardwick) and he confirmed that yellow is probably the best colour for attracting insects, followed by white. Red, blue and green are much better at not attracting insects. Now different insects have different colour preferences, and it very well could be that the white tyres are keeping a few insect species away, but most would be attracted to white. Think of all the white and yellow flowers in the world.
I imagine one could design a very interesting experiment that uses tyres painted different colours and measures differences in insects, soil temperatures and plant productivity.
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