The Soil Triangle
Continuing with Farmer Al’s presentation entitled “Compost: the new rage in sustainability”, we will refer again to one of the introductory slides with the heading “Soil texture at Frog Hollow Farm”. In reference to that slide, questions have been asked as to what is clay loam (a highly productive soil at FHF) and how can one go about identifying the type of soil present in a backyard garden.
Soil is defined by texture and structure. If we compare soil to a house, texture describes all the building blocks from which a house is constructed (clay, sand, silt). Structure defines how the building blocks are put together (walls, rooms etc…): organic matter, bacterial products, fungi and other substances act as cement forming stable clumps of soil.
Most soils are some type of loam which is defined as a mixture of sand, silt and clay that exhibits the PROPERTIES of these colloids as if they were
in equal proportions (40%-40%-20%).
Clay loam is a soil mixture that contains more clay than other soil mixtures. The particles of clay are very small (smaller than sand and silt), which is one its most important characteristics. A spoonful of clay has the surface area the size of a football field. This large surface area means that clay adsorbs a lot of water and other important micronutrients. This of course is very important for plant growth but at the same time this is one of the drawbacks of clay: it drains poorly. Try walking in the orchard after a heavy rain.
How can clay loams be improved to create better drainage without too much difficulty? The addition of well managed compost and/or humus will improve the structure of the clay loam through the formation of soil clumps or aggregates. The core of the clump is some combination of clay, sand and silt. This core gets covered with organic matter, bacterial glues, fungal strands, plant roots and this becomes a pretty stable clump of soil.
How can you determine the texture of your soil? You can use the “feel “ method (a most valuable skill used by field scientists).
Take a walnut sized sample of your moist soil and knead until it becomes like putty. Add small amounts of water if necessary.
While working the sample, does it feel silky smooth and it doesn’t stick to your fingers? Does it feel gritty and rough? Can you make a ribbon using your thumb and forefinger? This method identifies silty soils, sandy soils and clay soils.
For example, if you use this method with some of the soils present at Frog Hollow, the results are as follows:*Soil is moderately sticky and at the same time firm
*There is a little bit of grittiness (you can hear it when you rub it next to your ear)
*The sample is smooth but not too much
This seems like a very primitive method of assessing soil texture but try it with different soils around your home (garden soil, compacted soil) and pretty soon you will see how practical it is.
Finally, you can go to the National Resources Conservation Service site (NRCS) and using the Web Soil Survey you should be able to find out a soil description of the plot around your house (soil scientists have completed a detailed soil survey of the USAS).
“It is embarrassing not to agree on what soil is. In this pedologists (soil scientists) are not alone. Biologist cannot agree on a definition of life and philosophers on philosophy” Hans Jenny , “The Soil Resource: origin and behavior”
This blog has been inspired by the soil textbook edited by N.C. Brady and R.R. Weil, “The nature and properties of soil”.
Author: Christophe Kreis MLF Soil Consulting PhD, Molecular Biology/Developmental Biology, University of British Columbia, Canada. Christophe is co-founder of MLF Soil Consulting with his wife Monique. He started his career in basic medical research and after various positions in academia and industry Christophe slowly returned to his first passion Soil Ecology and Microbiology. It is his belief that human health is tied intimately to soil health through the production of healthy food. For this reason MLF Soil Consulting is committed to help farmers improve the management of their soil through composting, vermicomposting and biological analysis of microbial soil life.