1. Soil Formation Soil horizons - layers of soil renewal
- parent material
- erosion
- organic material
(type and amount depends on biome)

2. Soil Formation Inorganic rock/mineral material
Clay -- Silt -- Sand (particle size)
Organic material
Type and amount depends on biome
The percentage of each of these 4 components in any given soil has a profound effect on the soil’s characteristics and its productivity.

3. Nitrate & Phosphate & Potassium NO3- & NH4+, PO43-, K+
Soil Macronutrients and pH
3 most important and commonly tested nutrients:
Nitrate & Phosphate & Potassium
They are found in the soil as:
NO3- & NH4+, PO43-, K+
The appropriate levels of these nutrients determine a soil’s productivity.

4. Most plants grow best in slightly acidic soil:
Soil Macronutrients and pH
Most plants grow best in slightly acidic soil:
pH between 6.0 and 7.0
pH can determine a soil’s ability to absorb nutrients and exchange ions. Some plants are sensitive to changes in pH.

5. Soil Ion Exchange Capacity
A soil’s ION EXCHANGE capacity is an indicator of how suitable a soil is for long-term farming.
It can also inform the farmer as to the best method for fertilizing the soil (replenishing lost nutrients).
A low ion exchange capacity (usually sandy soils) would suggest the need for supplemental fertilizer application at frequent intervals. A high capacity (usually clay soils) would suggest a longer interval between applications.

6. Soil Ion Exchange Capacity
Why is a soil’s ability to exchange ions important?
The higher a soil’s ion-exchange capacity, the more nutrient ions (such as phosphate or potassium) it holds, AND the less likely it is that water will wash the nutrients away.

7. Water-holding Capacity & Permeability
Highly productive soil retains (hold) some water and nutrients, but is permeable enough to allow some to pass to lower layers.
Soils with a higher water-holding capacity will lose fewer nutrients due to leaching. Clay and silt have higher water-holding capacity than sand. Organic matter also increases a soil’s water-holding capacity.

8. Water-holding Capacity & Permeability
What is the role of water-holding capacity in agriculture?
Soil that can hold more water requires less rainfall or irrigation to support plants. In times of drought, soil with a greater water-holding capacity supports plants for a longer period of time.
However, in times of heavy or prolonged rain, soils with a high water-holding capacity can cause problems for plants (such as root rot) due to a lack of air in the soil.

9. Water-holding Capacity & Permeability
The more permeable a soil is, the more easily nutrients can pass from upper soil layers to lower soil layers.
Smaller particles (clay) have a greater surface area and hold more water. But they are also less permeable to water because they pack tighter together.
Sand is the most permeable but also has the least water-holding capacity.

10. Water-holding Capacity & Permeability
What is the role of permeability in plant production?
Most plants grow best in soils that water can penetrate. These soils allow for an adequate amount of air. Lands that have soil that allow for water penetration will have less runoff and, therefore, less soil erosion.

11. Determining Soil Type based on Particle Size Distribution
Knowing the Soil Type allows predictions to be made about ion-exchange capacity, permeability and water-holding capacity.
Testing would still need to be done to determine nutrient levels in the soil and it’s pH.

12. What are the basic soil conditions needed by plants?
Plants need adequate macronutrients.
Plants need soil with adequate water drainage.
At the same time, plants need a soil with sufficient
water retention.
Plants need soil with a high ion-exchange capacity.
Plants (generally) need a soil with a neutral or slightly
acidic pH

13. Finish Soil Testing!
Complete Soil permeability and Capillary Action
Saturated sample and Dry Sample
Use the soil triangle to determine Soil Type from your particle-distribution analysis.
Clean up your soil (keep soils out of sink!)