Week 1: Soils Flashcards
What are the 5 ecological roles of soil?
Supporting Growth of Plants, Control over Water, Recycling, It’s a Home, It’s a Foundation
What are the 6 things soil does for plants?
Provides physical support, provides ventilation through soil pores, stores water and channels excess away, moderates temperature, protects plants from toxins, provides inorganic mineral nutrients
What makes good quality soil?
Soil solids (Minerals 45%, Organic Matter 5%) + Pore Space (Air 20%-30%, Water 20%-30%)
What are the three main soil minerals in order of visibility?
Sand, Silt, Clay
What is organic matter made of?
Dead and living carbonaceous substances
What trait does soil with a high organic matter content have?
It’s darker.
What function does organic matter play in the soil?
It increases the soil water holding capacity and the cation exchange capacity. It binds soil particles together
Does organic matter directly provide nutrients to plants?
No – it is decomposed by soil organisms and the PRODUCT of its decomposition is the nutrient source for plants.
How is organic matter lost from the soil?
Through microbial respiration and the release of CO2.
What nutrients are made available by organic matter? What nutrients are not?
All except, Hydrogen Oxygen Carbon.
What composes the soil biota? In order of level but also whatever.
Bacteria, Actinomycetes, Fungi, Algae, Protozoa, Nematodes, Mites, Earthworms
How is soil water retained?
As a thin film on the soil particle surface or in soil capillaries.
How is soil water lost?
Mainly through the process of evapotranspiration. Soil evaporation and plant transpiration.
What’s a physical barrier often applied to soil which reduces water loss? By what percentage?
Mulches — by 33%
What benefit does proper soil aeration provide to plants? At what percentage of aeration are the benefits significantly inhibited?
Plant growth and microorganism activity increases. It decreases dramatically if the soil air content drops below 10%.
How does soil aeration work?
Plants release carbon dioxide (CO2) and Oxygen (O2) is diffused into soil.
What does soil texture refer to and how is it measured?
The size of particles that constitute the soil, measured by the percentage of clay, sand, silt.
What is soil structure?
The binding of individual soil particles into aggregates. Like the chunks of soil that emerge when you dig up some dirt.
What does soil structure and aggregates reflect?
The physical and chemical soil properties as soil activity produces the glue that holds the chunks together.
What’s the glue that binds aggregates?
Bacterial slime proteins, Fungal sticky proteins, Worm castings, Fungal and Root Exudates (secretions)
What’s the role of water chemicals and electrical charges re: organic matter + clay in soil structure?
The charges on the surface of clay and OM attract each other while water chemicals act as the binding glue.
What is the Cation Exchange Capacity (CEC)?
The sum total of exchangeable cations a soil can hold.
How do negative and positive charges work in the CEC?
So the soil particles clay and humus have a negative surface charge – positively charged ions (cations) attach to the surface while negatively charged ions (anions are repelled.
What are some important cations that attach to negative soil particles?
Calcium, Potassium, Sodium, Iron, Magnesium, Ammonium, Hydryogen
What role do root hairs play in the CEC?
Root hairs use hydrogen protons as exchange for cation nutrients?
So explain the CEC to me!!
Soil particles with negative charge attract + cations (like hydrogen (H+), iron (Fe+), magnesium (Mg2+), calcium (Ca2+), ammonium (NH4+) , sodium (Na+) but repel negative ions like chlorine (Cl-) and Nitrate (NO3-). Meanwhile the root hairs exude positive hydrogen cations OR free them through a partial dissociation of carbonic acid. So when the carbon dioxide exuded from the roots meets water (CO2 + H2O), carbonic acid is formed (H2CO3). Carbonic acid is a weak acid that can donate an H+ proton – so it usually breaks down into HC03- AND H+. The hydrogen (H+) ion reattaches to the clay which releases a cation into the soil like Iron (Fe+)
What is pH?
A measure of the hydrogen cations in a solution. As hydrogen (H+), increases the pH decreases.
Why is pH important?
It determines what can live in the soil. It affects the availability of nutrients. For example, in strongly alkaline soil, uptake of iron, manganese, and calcium are significantly impaired.
What are the (3) macronutrients soil receives from air and water?
Hydrogen, Oxygen, Carbon
What are the (6) macronutrients soil receives from soil solids like organic matter?
Nitrogen, Phosphorus, Potassium, Calcium, Magnesium, Sulfur
What are the (9) micronutrients soil receives from soil solids?
Iron, Manganese, Boron, Copper, Zinc, Chlorine, Cobalt, Molybdenum, Nickel
What are the 4 reasons plants need a continuous supply of water?
To transport nutrients, maintain turgor, regulate temperature, remove waste and exudes.
What is the maximum retentive capacity of soil?
When every soil pore is filled with water. The soil is saturated.
What is gravitational water?
Water occupying large soil pores that will drain due to gravity.
What is field capacity?
When all the water has drained leaving only the micro-pores and bound water.
What is water holding capacity?
The amount of water that remains at field capacity.
What is wilting point water?
The amount of water in the soil that the plant can’t absorb. The plant will wilt.
What’s the calculation for Plant Available Water?
Field capacity - Wilting Point Water = Plant Available Water
