Week 1: Soils

Question 1

What are the 5 ecological roles of soil?

Answer 1

Supporting Growth of Plants, Control over Water, Recycling, It’s a Home, It’s a Foundation

Question 2

What are the 6 things soil does for plants?

Answer 2

Provides physical support, provides ventilation through soil pores, stores water and channels excess away, moderates temperature, protects plants from toxins, provides inorganic mineral nutrients

Question 3

What makes good quality soil?

Answer 3

Soil solids (Minerals 45%, Organic Matter 5%) + Pore Space (Air 20%-30%, Water 20%-30%)

Question 4

What are the three main soil minerals in order of visibility?

Answer 4

Sand, Silt, Clay

Question 5

What is organic matter made of?

Answer 5

Dead and living carbonaceous substances

Question 6

What trait does soil with a high organic matter content have?

Answer 6

It’s darker.

Question 7

What function does organic matter play in the soil?

Answer 7

It increases the soil water holding capacity and the cation exchange capacity. It binds soil particles together

Question 8

Does organic matter directly provide nutrients to plants?

Answer 8

No – it is decomposed by soil organisms and the PRODUCT of its decomposition is the nutrient source for plants.

Question 9

How is organic matter lost from the soil?

Answer 9

Through microbial respiration and the release of CO2.

Question 10

What nutrients are made available by organic matter? What nutrients are not?

Answer 10

All except, Hydrogen Oxygen Carbon.

Question 11

What composes the soil biota? In order of level but also whatever.

Answer 11

Bacteria, Actinomycetes, Fungi, Algae, Protozoa, Nematodes, Mites, Earthworms

Question 12

How is soil water retained?

Answer 12

As a thin film on the soil particle surface or in soil capillaries.

Question 13

How is soil water lost?

Answer 13

Mainly through the process of evapotranspiration. Soil evaporation and plant transpiration.

Question 14

What’s a physical barrier often applied to soil which reduces water loss? By what percentage?

Answer 14

Mulches — by 33%

Question 15

What benefit does proper soil aeration provide to plants? At what percentage of aeration are the benefits significantly inhibited?

Answer 15

Plant growth and microorganism activity increases. It decreases dramatically if the soil air content drops below 10%.

Question 16

How does soil aeration work?

Answer 16

Plants release carbon dioxide (CO2) and Oxygen (O2) is diffused into soil.

Question 17

What does soil texture refer to and how is it measured?

Answer 17

The size of particles that constitute the soil, measured by the percentage of clay, sand, silt.

Question 18

What is soil structure?

Answer 18

The binding of individual soil particles into aggregates. Like the chunks of soil that emerge when you dig up some dirt.

Question 19

What does soil structure and aggregates reflect?

Answer 19

The physical and chemical soil properties as soil activity produces the glue that holds the chunks together.

Question 20

What’s the glue that binds aggregates?

Answer 20

Bacterial slime proteins, Fungal sticky proteins, Worm castings, Fungal and Root Exudates (secretions)

Question 21

What’s the role of water chemicals and electrical charges re: organic matter + clay in soil structure?

Answer 21

The charges on the surface of clay and OM attract each other while water chemicals act as the binding glue.

Question 22

What is the Cation Exchange Capacity (CEC)?

Answer 22

The sum total of exchangeable cations a soil can hold.

Question 23

How do negative and positive charges work in the CEC?

Answer 23

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.

Question 24

What are some important cations that attach to negative soil particles?

Answer 24

Calcium, Potassium, Sodium, Iron, Magnesium, Ammonium, Hydryogen

Question 25

What role do root hairs play in the CEC?

Answer 25

Root hairs use hydrogen protons as exchange for cation nutrients?

Question 26

So explain the CEC to me!!

Answer 26

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+)

Question 27

What is pH?

Answer 27

A measure of the hydrogen cations in a solution. As hydrogen (H+), increases the pH decreases.

Question 28

Why is pH important?

Answer 28

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.

Question 29

What are the (3) macronutrients soil receives from air and water?

Answer 29

Hydrogen, Oxygen, Carbon

Question 30

What are the (6) macronutrients soil receives from soil solids like organic matter?

Answer 30

Nitrogen, Phosphorus, Potassium, Calcium, Magnesium, Sulfur

Question 31

What are the (9) micronutrients soil receives from soil solids?

Answer 31

Iron, Manganese, Boron, Copper, Zinc, Chlorine, Cobalt, Molybdenum, Nickel

Question 32

What are the 4 reasons plants need a continuous supply of water?

Answer 32

To transport nutrients, maintain turgor, regulate temperature, remove waste and exudes.

Question 33

What is the maximum retentive capacity of soil?

Answer 33

When every soil pore is filled with water. The soil is saturated.

Question 34

What is gravitational water?

Answer 34

Water occupying large soil pores that will drain due to gravity.

Question 35

What is field capacity?

Answer 35

When all the water has drained leaving only the micro-pores and bound water.

Question 36

What is water holding capacity?

Answer 36

The amount of water that remains at field capacity.

Question 37

What is wilting point water?

Answer 37

The amount of water in the soil that the plant can’t absorb. The plant will wilt.

Question 38

What’s the calculation for Plant Available Water?

Answer 38

Field capacity - Wilting Point Water = Plant Available Water