Good day RG family
I have been using the Keen-Rackzowski method for determining water holding capacity. I have been getting really good results with this method and it's correlating very well with other know soil indicators that improve water holding capacity of soils. The problem is with one set of soils that I am working with. These soils do not absorb water, instead the water stays on top of the soil sample and forms a bubble or runs to the sides instead of infiltrating. What can I do to overcome this problem in the lab? And what causes soil to repel water?
Thank you in advance for your responses.
Kind regards,
Portia
Hot wildfires is one cause that alters charge on soils, repelling water. It typically goes away with time And rainfall events. Unsure, but you might try adding some mild detergent to solution such as Dawn detergent to increase absorption. I would not know how much to add, start small with a drop or two in solution. I don’t think you want suds.
Dear Portia, Some publications may be relevant
www.journalrepository.org/media/journals/.../Olorunfemi382013JSRR7325_1.pdf mgsantaclara.ucanr.edu/garden-help/watering-hydrophobic-soil
https://www.slideshare.net/Hanumanthnw/hydrophobicity-of-soils
Chapter Hydrophobicity of Soil
I forgot to mention a chemical polymer called PAM. We did a few tests with PAM on poor gullies soils, and there were a few publications or report briefs of how it helps improve infiltration. With rainfall, it forms like a goo that holds water and helps water move into soil. On areas that have experienced severe wildfire, it may be helpful and brief reports of its use should still be available. Not all soils seem to develop water repellent soils, as more common In say Colorado or some drier Pacific Coast areas which have a periodic dry or drought season with severe wildfire potential, while seldom in my limited experience seen in southeast USA with more frequent rainfall events.
Thank you for your responses, I am not sure if the soils have any history of sun baking or affected by wild fires that I still have to find out. I will try out the detergent idea today and see if the soil absorbs moisture. Just one other point to note, the soils I am working with have a high carbon % i.e. >4%, I am just a bit surprised that soil's with such carbon levels will have trouble absorbing water.
Dear Portia Among the causal factors of soil hydrophobicity are the carbon fractions resulting from the decomposition of organic matter such as lipids. To study the effect of hydrophobicity, you can use a wetting agent. There are several on the market. Good luck
Perhaps there are very small pores in the soil. Water due to surface tension does not penetrate into such pores. Try to mix the soil after it is moistened.
Hi Portia,
You may already have worked out your problem with water-repellent soils ...
Why does soil repel water? Or why can't the water immediately infiltrate into a dry and humus-rich soil like in your case?
The reason for the drop formation on dry and humus-rich soil is the surface tension of the water. The cause of the surface tension is the dipole character of the water molecule. Simplified described, the water molecules attract each other by this dipole character and form hydrogen bonds among themselves. This results in the formation of droplets on the surface. The cohesion forces are greater than the adhesion forces between the water molecules and the soil particles.
In general: the drier and more humus-rich and coarse-grained the soil is, the stronger the water-repellent effect of the soil is.
In addition, waxes and fats produced by microorganisms can increase the water-repellent effect.
What to do, to rehydrate your dry soil samples.
I guess you have your soil samples in soil sampling rings. I would put them in a shallow water bath and wait between 2 and 7 days depending on the soil texture, then the dry water repellent soil samples should also be rehydrated.
I recommend not to use dishwashing detergents for an investigation of the water holding capacity. A detergent can change the surface tension of the water and may cause an error in the test.
Best regards from Germany, Stefan
RMJ 50
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