How does lime flocculate clay soil

[emma69]

Hello guys, I have another question for you that I am stressing myself over, I would value your insights. Thanks in advance.

When you add lime (Calcium carbonate) to clay soil it flocculates it and improves the structure, how does this happen ?

 

[William Turley]

I don't have a direct answer to your specific question but I found a video that explains the process of flocculation and may help your understanding.
https://www.khanacademy.org/partner-content/mit-k12/mit-k12-materials/v/flocculation

In practice we have built a cob cottage. The cob mixture recipe is as follows...3-sand, 1-clay, 1-straw or grass, 1-horse manure, and 1/4 lime. All portions are by volume.
The end product is a beautiful sculptured habitat. Check it out...https://www.airbnb.com/rooms/4191617?checkin=03%2F18%2F2015&checkout=03%2F21%2F2015&s=MZbY

Good luck

 

[Baluncore]

Clays are layered silicates = phyllosilicates. The weak bonds between the silicon layers involve different chemical species that can be exchanged with the environment. With hydrogen or water between the layers, the clay will be very fluid. By changing the pH and reducing the availability of hydrogen, a heavier element such as Li, K, Na or Ca can enter between the silicate layers and make the clay more physically stable.
http://en.wikipedia.org/wiki/Clay_minerals#Structure
http://en.wikipedia.org/wiki/Cation-exchange_capacity

 

[FainAvis]

On building sites we often get vehicles stuck in the mud, sometimes because it rained after the vehicle was positioned. Rain water is especially soft and makes some muds very slippery. But a neat trick is to dump lime in the rut. Lime "hardens" water. The vehicle can get better traction.

 

[emma69]

Hello again guys, still on the flocculation thing. According to J.B. Page (ROLE OF PHYSICAL PROPERTIES OF CLAYS IN SOIL SCIENCE pp.168) most clays soils are "already flocculated" so adding lime is not going to make any difference. This is quite an old text does his position still stand ? and if it does why are so many farmers buying lime to improve the structure of their clay soils, are they being conned ?. Thanks in advance.

 

[Geology Erwin]

Lime does influence soil acidity trough its carbonate part. The acidity in turn affects the availability of nutrients to plants and the formation of aggregates in the soil. In Flanders (Belgium) farmers us lime to improve the macroporosity or structural porosity of heay clay soils. This is supposed to work by making the the clay aggregates more brittle so that you can plow better/eassier/cheaper. I'm no farmer so i don't have experience with this. However in home gardens in Flanders there is generally to much lime in the soil. people use lime the reduce the growth of mosses in their lawns. That is indeed a conn. Some lawns benefit from lime but it generally takes years before yiu need to add more lime.

 

[Baluncore]

still on the flocculation thing

I think the term "flocculate" is being misapplied to soil structure. Flocculate has meaning in a fluid solution but not in a soil.

The clay layer in a soil can prevent air and water moving through the soil. If clay can flow and forms a pan then the soil will have problems. Clay is less of a problem if it is more physically stable and less able to flow. Lime changes the pH and so increases the stability of the clay, improving the structure of the soil.

Physical cultivation is an expensive and aggressive way to break the pan and can result in erosion. But a clay pan can be broken by processes such as growing deep rooted plants. Growing a root crop like parsnips in a clay soil can puncture the pan and so permit air, water and chemical exchange. The crop should be mown while the roots must be left in place to form organic columns through the pan that then allow chemical exchange. That remedial change may be self perpetuating or it might be maintained by the addition of lime to the surface.

 

[DarioC]

Interesting baluncore. Like natural mulching.

Speaking of clay, I ran into something that made me blink. I do samples from the back and front yard and various water holes and make wet micro organism growth jars to check with the really fine microscopes I got surplus from UC Davis. When I look at the clay (adobe) from here in central CA that I always get in my viewing sample it seems to indicate (at 400 X say) that adobe is all very,very fine sand. Rather goes against my previous perception that clay absorbs water. I mean in the sense that the water is taken into the particle like fiber would.

If it is just super fine sand it would explain a lot about it's behavior. Have I got a good read on that? Hope this is close enough to the original question to be appropriate here.

DC

 

[Baluncore]

How do you differentiate between fine sand and clay?

Maybe the clay has blown away or been moved deeper into the soil profile.

When I look at the clay (adobe) from here in central CA

What do you mean by “adobe”?

 

[Ophiolite]

Clay has two distinct definitions, both correct. When referring to clastic sediments, and I think, soils, clay generally relates to the size of the particles. On the Wentworth scale, anything smaller than 1/256th of a millimetre is classified as a clay. Alternatively, a clay is a mineral - a phyllosilicate, as mentioned earlier by Baluncore.

Most clays (soils/sediments/rocks) contain a high to very high percentage of clay minerals, but I have seen analyses where more than 70% of the clay was silica. This is not surprising, given the far greater resistance to chemical and physical attack of silica over clay (mineral).

On the term flocculate, I have only been exposed to this in relation to drilling fluids. These often contain clays, either from drilled formations, or - very often - montmorillonite clay that is added to give the drilling fluid desirable properties. Flocculation in this scenario is the clumping of clay particles in response to the presence of cations, as mentioned previously. I can envisage a similar clumping occurring readily enough in soil

 

[spodosol]

Flocculation and dispersion are processes in soils that describe the attraction or repulsion of clays. Dispersion is when cations on the negatively charged surfaces of clays do not fully cancel out the negative charge and so these clay particles are repulsed from one another. Flocculation is the opposite process where the cations on the clay surface exert such a strong pull that they cancel out the repulsive force of the negatively charged clays and pull them closer together. Examples of dispersion in soils are when you have sodium (Na+) on the clay surface which only moderately cancels out the negative charge of the clays. As such the clays push each other apart, they separate and easily flow into solution, and then you get clays plugging up all the soil pores creating an impermeable layer. Flocculation can happen when you have lots of magnesium (Mg 2+), a relatively small cation, occupying most of the exchange sites on the clay. This pulls the clay tightly together. People will sometiems add gypsum (CaSO4) is order to replace the Mg2+ with Ca2+ which is a larger cation and so occupies more space on the clay for the same amount of charge, effectively reducing the amount of positive charge the clay experiences. Below you can see where clay was flocculated on the right. Lime, (CaCO3) was added and the Ca2+ acted to flocculate the clay relative to the column on the left. http://www.pasture4horses.com/soils/soilflocculation.jpg