A Look Behind the Second Step

Science and Sustainability

Ok, I started to write this week's installment on xeriscaping, which concerns soil, and soil amendments.  However I got sidetracked by the science behind the soil.  What can I say?  Science interests me.  Besides, human beings are at a point in their evolution where we are able to see the impact we are having on the world around us, thanks to the science.  Sustainability is applying the science to even the most routine tasks, with the goal of lessening our presence.

<Insert Pun on Dirt and Soil Here>

Once you have layed out the design for your water-saving landscape, you should turn your attention to the soil.  Soil plays a large role in any landscape, and musn't be overlooked by the eager sustainable gardiner.

Hydrology + Geology =? (Warning, Scientific Content)

Soil is more than just tiny rocks.  This is what separates Earth from the moon!  (Aside from atmosphere, and water, and the lower gravity and, quite a lot of things actually ...)  The worn-down rocks, as it were, classified by size, are called 'regolith', and this is the substance that coats the moon.

No gardens here!

The classification of soil particles are sand, silt and clay, sand being the largest, while clay is the smallest.  However, delving into technicality, some clay particles can fall into the silt size, while some silt particles can be as small as clay.  So what is the difference there?  Well, sand and silt are formed by the physical and chemical weathering of rocks, while clay is formed by chemical processes that form solutes (molecules and substances that don't dissolve in water).

Volcanic Soil

Right about now you are probably thinking: Why do I care?  I have a point, I promise.  The size of the particles in your soil dictates how quickly water drains away!  Larger particles, such as sand, and even gravel, create large porous areas, and this allows water to escape quickly, whereas smaller particles will retain water longer.  Yet is not just easy access formed by those large pores that encourages water evacuation.  Clay has an overall greater surface area, that makes the water stick to it, which helps retention.

I know, I know, it sounds crazy, but this is the principle by which golf greens are formed.  The water is stuck to the soil particles through the Electromagnetic Forces (EM), and pulled away by Gravity.  EM is stronger than gravity, which is easily demonstrated:

Jump.  Gravity pulls you down to the ground, but you don't go any further.  If gravity was the strongest force, you would continue falling to the centre of the earth.  The electromagnetic forces formed by the molecules in your feet are repelling the EM of the molecules in the ground.  The repelling action of these miniscule particles is enough to combat the gravity of the entire planet.  It turns out that gravity is quite weak. 

Soil = Regolith + Organic Matter

Soil Horizons
O = organic matter
A = top soil
B = sub soil
C = unweathered rock

Really then, what makes the soil is the organic matter, or humus that is found within.  Organic matter is broken down residues of life.  Like Mufasa explained to Simba, 'when we die, our bodies return to the ground, and nourishes the grass, and the antelopes eat the grass, therefore we are all part of the Circle of Life'.  Cue inspiring musical number.  (Of course, due to modern undertaking processes, human bodies are more preserved, and don't break down nearly as quickly, but that is another matter altogether.)

Organic matter can be formed from anything, both decaying plant and animal remains.  Organic matter has many functions in the soil, and the content of organic matter can dictate the difference between sucess and failure when it comes to plant growth.  The organic matter improves water and nutrient storage, as well as creating optimal conditions for nutrients in the soil to become available.  (Humus is slightly acidic, and a change in pH can alter the rate of solubility of nutrients.)  Organic matter will also create aggregates in soil, which can improve permeability - water will be absorbed more easily. 

Tune in Next Week

So how can this be applied to water conservation?  Next week I will take a look at different amendments, and how they can be tools in xeriscaping, as well as the pros and cons of each one.