Next: Rocks Module 25
Igneous (fire)
Sedimentary (layers)
Metamorphic (Kafka rocks, just kidding: changed by heat and pressure)
Igneous= directly from magma, can be either basalt (low melting point, like our island or oceanic plates) or granite (lighter, what continents are made of)
Granite breaks down into light colored sand, makes for fertile soil. Basalt (like us) can make sand too, but less fertile (e.g. black sand beach).
Sedimentary= just like it sounds, from mud, sand or dust, usually in layers.
Metamorphic= changed by heat and/or pressure (slate, marble or coal)
Soil-formed by weathering (chemical or physical) of parent rock
Erosion can be by water or air (wind)
These used to be just A, B, C layers
E layer was added (eluviated layer-where water washes out nutrients)
O layer was added (overlayer-detritus)
Latest version:
Soil structure (physical analysis)
n.b. the trick to reading the lines is always look clockwise...
Finer soils drain slowly (capillary action), hold nutrients (because of reduced water flow), and settle last in rivers
Coarse soils (e.g. sand) drain quickly, are nutrient poor (water washed the nutrients away) and settle first in rivers
Loam is the term for a perfect balance of these inorganic soil types
Farmers refer to "tilth" of a soil, which includes ability to hold water, organic content and more:
Organic matter is not included here: it holds water and decomposes, releasing nutrients
For healthy soil, we need both the physical (above), organic and chemical systems to balance.
Chemical analysis:
N=nitrogen: critical for plant growth
P=phosphorus: roots and fruits
K= Kalium=Potasssium=potash: plant immunity
pH is the Hydrogen ion content: pH of 7 is neutral water, others may have other values
Hydroponics use a term EC for Electrical conductivity, which is a measure of dissolved ions in solution.
1.5-2.5 is ideal for most hydroponic systems, depending on plant types
See also CEC: Cation exchange capacity
Lab:
Physical tests----
- Gross analysis: how does the soil feel in your hands: like clay or sand? Does it have organic matter? Can you squeeze it and have it hold shape (tilth)? What color do you see?
- Percolation test: time it takes water to move through a soil sample, measured in cm/second. Measure the seconds, and the cm depth of your soil, divide.
- Sedimentation test: settled layers after mixing with water, measure total thickness, then layer thickness, present at percentage of total
- Dry sifting test: drop your sample into the sifter column, measure mass of each layer
Chemical tests----
- Decant (pour off) liquid from the sedimentation test above, use for the pH test kit
- N test: same with the N soil test kit
- P test: same with the P soil test kit
- K test: same with the K soil test kit
- (optional) organic matter test: bake the sample, mass before and after, difference is organic matter
Desertification:
Usually from removal of native plants, overgrazing and/or over-irrigation with well water (salinization)
Solutions:
Comments