Why can't you change soil texture

[emma69]

Hi, there appears to be a consensus in the literature that you can't change soil texture (not structure!). Many texts state this but they don't say why. If I have half a bucket of clay soil and mix in the correct proportion of sand, why isn't this a sandy loam ? I am having trouble with this. Thanks in advance.

 

[rootone]

Soil textures are classified by the fractions of each soil separate (sand, silt, and clay) present in a soil.
So of course you can make different textures by mixing things differently.
The ratio of different constituents is the definition of a soil texture.
Can you give an example of literature which contradicts this?, possibly you misunderstood?
Maybe the intended meaning is that there are definitions of soil texture, and you can't change the definitions arbitrarily.
You can change soil itself though.

 

[emma69]

Thanks for getting back to me, I am certain that i didn't misunderstand, however i will fish out a few examples shortly.

 

[jim mcnamara]

I take not possible == not feasible. That is probably what is meant.

Changing soil texture on a 3 hectare field is an economic as well as an engineering challenge. Texture in the top 2cm is not as important as larger portions of the soil column in determining some properties of soils. So what I see is, in your example: remove the top 20cm of soil, admixing 20% sand and replacing it in situ.

Ignoring the fact that the soil layer is now thicker than before, I think you can see that it would cost a LOT of money to do this. Or an incredible amount of time and labor. It is not really practical except for people working the soil at the highest end of the technology spectrum. So, adding soil amendments is a less expensive way to ameliorate adverse soil conditions than actually altering the physical texture - note the limited scope (and cost therefore)-
http://www.ext.colostate.edu/pubs/garden/07235.html

Just because something is theoretically possible, does not mean people who have to make a living in that domain are going to do it. Example: I can walk around the world. Nobody will claim it is physically impossible. But will I get all the way around without running afoul of some nutty government official or religious fanatic? Will I have food and water? Will I have health care if I need it? Those are feasibility tests. These issues may involve one or more of: time, cost, and legal hassles.

None of which says, 'hey you cannot do this' in the personal physical ability sense.

 

[Universal Nerd]

Of course you can change soil texture and structure, by adding stuff or treating it in some way, such as high heat (which may change the soil physically for the better or worse or not at all). As mentioned above, the problem is cost. Unless you're growing very intensive crops (high profit per unit of land area), physical texture/structure additives rarely pay off, unless that additive material is cheap and easy to distribute onto the fields.

There are, however, probably many examples around the world - currently, and throughout history, where people have added material to improve soil texture/structure. One example is the "magic" soil called "terra preta" made by pre-Colombian Amazonian tribes. I think the most important component was charcoal (or "biochar" as they call charcoal now when applied to soil improvement). Also, everyday home gardeners may add various things to improve soil texture/structure. Of course most home gardeners are not trying to make a profit though, so they can afford to screw around and put in more value than they get out. Many biological materials (wood chips/saw dust, leaves, sphagnum moss, etc.) can be added to improve soil structure (and plant nutrients), until they decompose entirely. Also, "green manure" crops or "cover crops" are plants grown in a field specifically to improve soil fertility, manage erosion or improve soil structure.

 

[emma69]

Thanks for your replies but I am still struggling with this. When you add sand to clay, a different reaction takes place to what happened to when a sandy loam developed and you end up not getting this but something closer to concrete, which is undesirable for growing things. Whats the difference ?

 

[Universal Nerd]

Just off the top of my head, I'll say it may have to do with the physical properties of clay and sand, and a little to do with the chemical properties of clay also. I'm not an expert in this, so maybe someone can provide better input, but I have been messing with plants (and therefore with soil too) since I was 8. I've tried mixing sand with clay soil many times, because it seems at first glance it should be an improvement, but clay mixed with sand does seem to form a sort of temporary, weak concrete (until it becomes wet again), is it not much better than the clay alone is. In fact, clay baked at very high temperatures is one of the ingredients of Portland cement, the key ingredient of conventional concrete. Clay and sand are also the main components of many conventional brick recipes. I think what goes on is that clay particles surround and coat every relatively-large sand particle, thereby separating the sand particles from each other and retaining a tight physical fit, so that air and water still can't move through well. I think temporary weak the clay also forms weak chemical bonds with itself and other particles as the clay dries, almost like a weak glue. Organic particles that make up a loam are shaped differently and are mostly much larger than clay particles, can let moisture flow through much better, can chemically react with things better, and attract/harbor microorganisms - anything from bacteria to worms, which further help air and water move through the soil.

The ratio of the soil components would be very important too. For example, I imagine a clay-loam mix would suddenly grow plants much better once the loam content reached a certain percentage (depending on the exact properties of that type of loam), because at some point, many loam particles would be touching each other, providing a 3-D web through which water, air and nutrients could flow, and roots could penetrate easier.

 

[Universal Nerd]

Kind of related... I lived in South Florida for a couple years and I wondered why the soil was so poor there. It was very sandy, with not much organic matter. Rainfall wasn't retained well by the soil for use by plants. The high sand content seemed to make the water drain though and evaporate fast. I googled about it a couple years ago. If I understood right, South Florida soils are poor because of all the sun and heat (for more of the year than up north), combined with ample moisture. The heat and moisture allows microorganisms to more completely digest that organic matter before it can accumulate in the soil. So microorganisms are effectively turning that organic matter to carbon dioxide before it can become soil. I assume this is why soils can be good in Canada, but poor in Amazon rain forests (an even more extreme case of heat and moisture). There have been some very rich soils in South Florida where swampland was drained. In a swamp (whether in north or south latitudes), organic matter can build up for thousands or millions of years because the acidity and lack of air underwater can slow the decomposition of organic matter. These rich, former-swamp Florida soils do start decomposing when drained and exposed to air though. Fields will "sink" inches over decades as microorganisms digest that organic matter to carbon dioxide (and many other various substances, of course).

 

[Lowedown]

Soil quality, texture, structure and composition also is influenced by the ecosystem and climatic region in which it is located. Altitude, temperature, seasonal fluctuations (floods and droughts), rainfall, and of course the interactions of living things (decomposers, scavangers, producers, etc.) all combine to alter or stabilize the soil. Even a salmon swimming up a river in the Pacific Northwest has an influence on the soil of the river ecosystem. Major limiting factors like periodic volcanic eruptions or earthquakes can have long term consequences on soil types. Flooding at river deltas has long been known to be a major influence on fertility and dams that restrict flooding can alter the productivity of the region. Good dirt is not cheap, it takes a long time to establish fertile soils and we all depend upon that thin layer of topsoil and the fact that it rains.

 

[davenn]

Thanks for your replies but I am still struggling with this. When you add sand to clay, a different reaction takes place to what happened to when a sandy loam developed and you end up not getting this but something closer to concrete, which is undesirable for growing things. Whats the difference ?

sand and clay doesn't make concrete or anything like it
rather, sand mixed with clay will break up the clay and make it more porous to water and easier for plant roots to move through.
This will make it better for plant growthDave

 

[Bystander]

Depends upon the specific "clay" mineral.

 

[256bits]

Thanks for your replies but I am still struggling with this. When you add sand to clay, a different reaction takes place to what happened to when a sandy loam developed and you end up not getting this but something closer to concrete, which is undesirable for growing things. Whats the difference ?

That would be the structure of the soil - how the particles aggregate.
As stated, on a small scale the texture can be changed, but it is impractable on a large scale, and futile.
On broad terms, it took millenium of years for the soil to come to the condition it is in, at a sort of semi-equilibrium state between all the components of different sizes.

for example, in hilly terrain,
Tops of hills may be sandy, and low areas composed mainly of smaller sized particles.
Adding clay to the top of the hill to improve its "quality" can work for a short time, but the soil will have a tendency to revert back again to sandy, with runoff carrying the clay downhill.
In the end, one has spent time and effort for nothing.
Other examples were cited in previous posts.