Do Now: From which materials do you think soil is made? Are all soils the same? Think of some ways that they are different?
Basics Soil is a major component of the biosphere It contains solids, liquids and gases Do you think that the contents of soil affect the types of plants that can grow in it? Are all soils the same? How would differentiate among them? Elicit aim
Aim: How are soils different and how are they classified?
Which types of materials do you think would affect the structure and texture of soil? Ex: How would you make a soil less compact and more airy?
You can add stuff to soil Rock make air spaces in the soil Perlite - volcanic glass that has a relatively high water content When used as an amendment it helps prevent water loss and soil compaction. Tree bark Does the same as rock Except lighter weight
Organic vs Inorganic List some common inorganic (non living, in other words, stuff that was never alive to begin with) materials found in soils
Erosion of bedrock (the hard rock at the lowest level of soil) and exposed rocks creates most of the inorganic content Where would organic material come from?
Humus not hummus Humus is the organic material in soil. The decomposed leaves and animal matter that cannot decompose any further. This is where the organic food of plants is found. Humus usually found on the top layer and is dark in color due to high carbon content Why do you think that humus is not usually found deeper underground?
Answer: Plants use it up The vertical dimension, exposed by excavation from the surface to the parent material, constitutes the soil profile. Layers in the soil, distinguished on the basis of color, soil texture, soil structure, and other visible properties, are called horizons. Several horizons make up the soil profile.
Unweathered Illuvial area with accumulated clays and elements like iron and aluminium in the lower soil horizons due to downward transport via water Eluvial soils made up of weathered material, and the accumulation of debris (organic or inorganic)
Texture of the soil The rougher the texture, the more air can be found in it. Order the following from least airy to most airy soil as best you can Sandy soil Clay filled soil Colloidal soil Silty soil Gravel filled soil
Answer Gravel Sand Silt Clay Colloidal (suspended in water) Loamy soils, Loams are a mixture of sand, silt and clay
Organic matter like humus can increase the acidity of soil (low ph) If the humus was made from plants that carry tannins, when they decompose the tannins will become Tannic Acid. Ex: Oak, Almond, & Magnolia leaves are rich in tannins Water rich in forest leaves often turns brown due to tannic acid
Can you think of another source of tannins? Hint; Boiling leaves brings out the tannins
Alkali, or alkaline, soils These are clay soils with high ph (> 9), a poor soil structure and a low water infiltration capacity. Often they have a hard calcareous layer at 0.5 to 1 meter depth. Alkali soils owe their unfavorable high ph mainly to the dominating presence of sodium carbonate.
Sodic soils In areas particularly with low rainfall, high sodic (high sodium content) and/or saline soils are more prevalent. Why?
Because there is less rainfall to leach the alkali and alkaline earth metals deep into the soil. Also there is less organic matter growing. Planting grass is a great way to lower the ph of alkali soils. Grass lives fast and dies quickly. Why do you think grass helps lower the ph of soil? Another method involves applying elemental sulfur and water which converts into sulfuric acid to lower the ph of soil. Both of these methods involve the synthesis of gypsum as the product of reaction. Gypsum, which is calcium sulfate (CaSO₄) can be beneficial in reducing sodium levels in the soil.
Soil ph Affects Nutrient Availability The ph of soil determines the availability of nutrients for the plants. A neutral ph from 6.2-7.3 is normally the most favorable for plant growth and development because the majority of the nutrients are available within this range.
Do all plants have the same ph preference?
Most perennial flowering plants prefer the 6.1-7.0 range. However, certain plants including azaleas, camellias, holly, and pine trees thrive in acidic soils such as 4.5-6.0.
At higher ph levels such as 7.8 and above, nutrients such as calcium and magnesium are more available for plant uptake. However, other nutrients such as iron, copper, zinc, manganese, and phosphorous are much less available.
How Acidic Soil is Modified When ph levels are very acidic the soil becomes overloaded with hydrogen cations. At this point plants are not able to effectively get enough nutrition. Low soil ph such as 5.6 or below can be improved by adding ground limestone to the soil.
Why limestone? The chemical reaction is: lime (CaCo₃) + hydrogen (H+) calcium (Ca++) + carbonic acid (H₂CO₃). Then the carbonic acid breaks down into water and carbon dioxide. H₂CO₃ H₂O + CO₂ This opens up the exchange sites in the soil thereby increasing the storage capacity of nutrients in the soil
The Classification of Soil types found in the world According to the USDA There are ten Soil Orders, differing in makeup, chemical and physical characteristics We will cover 5 Try to figure out which of the 5 is what you find here in the forests of NYC
Entisols Recent soils (newly made) with very little vertical profile development, and no diagnostic horizons.
Aridosols Shallow, stony soils of dry climates with high alkalinity and low organic matter content Alfiols Soils of regions with high to moderate levels of rainfall, with clay horizons. Associated with temperate forests, Mediterranean areas and tropical grasslands.
Oxisols Deep, highly weathered and leached soils of the humid tropics; red in color due to accumulated iron oxides; this is the soil of moist tropical forests Hawaii
Histosols/Bog Soils Dark organic soils of poorly drained areas; typically very acidic and of low fertility
Homework Find and describe techniques for composting so that we may make our own humus.