SCSC 105 Test #2

Define ecosystem. What are the five components of an ecosystem?

Collective function of organisms and their environment.

1. Food Chains

2. Diversity

3. Competitive Exclusion

4. Plant Succession

5. Nutrient cycles

Name important functions that ecosystems provide.

1. Carbon Sequestration

2. Climate Regulation

3. Erosion Control

4. Wildlife

Define agroecosystem

Ecosystems modified to produce food, fiber, and/or shelter

Compare nutrient cycling in agroecosystems

Nutrient cycles are altered, and inputs are required

What are two plant available forms of nitrogen?

1. Nitrate

   • NO_3^-

2. Ammonium

   • NH_4^+

Describe the differences and/or similarities of natural ecosystems compared to agroecosystems in terms to diversity, inputs, management, breeding, and nutrient loss.

Agroecosystems have low diversity, high input (Fertilizers, pesticides, labor), High management, high breeding, high nutrient loss.

Natural ecosystems have high diversity, no inputs, no management, no breeding, and no nutrient loss.

What are TWO risks associated with simplified agroecosystems? Give an example of a simplified agroecosystem from history.

1. Limited plant diversity

2. Problems become magnified

Ex = Wheat and Dust Bowl in the 30s

What are three important functions served by soils?

1. Anchor plants

2. Storage of water and nutrients for plant uptake

3. Habitat for soil organisms (bacteria, fungi, insects, and invertebrates)

Name the five soil forming factors

1. Climate

2. Organisms

3. Relief (topography)

4. Parent Material

5. Time

Name the 7 predominant soil orders in Texas

1. Mollisols

2. Vertisols

3. Ardiosols

4. Ultisol

5. Alfisols

6. Entisols

7. Inceptisols

What is soil organic matter (SOM)?

Portion of the soil that includes animal and plant residues in various stages of decomposition.

What are the five different functions of soil organic matter (SOM)?

1. Carbon sequestration

2. Nutrient Source

3. Soil aggregation and structure

4. Water storage

5. Chemical sequestration

As C:N ratio increases, what happens to decomposition rates of plant material?

The rate of decomposition decreases.

What are the three soil particle sizes?

1. Sand

2. Silt

3. Clay

Know how to use the soil textural triangle to classify soil by texture.

How to read:

1. Start on % sand and go up and left

2. % silt down and left

3. % clay strait across to the right

Define gravitational water, field capacity, and permanent wilting point.

• Water drains readily through the soil

• Water is held in the pore spaces and is readily available to plants

• Water is held tightly by soil particles and is not available to plants

What is soil tilth and what does it determine?

Physical condition of the soil as related to plant growth.

• ease of tillage

• root penetration

• aeration

• water infiltration/drainage

Define shrink-swell potential in soil. Why is it important?

A measurement of the amount of volume change that can occur when a soil wets and dries. It must be considered in structural or engineering project plans.

Compare and contrast soil particle size (sand, silt, clay) for water holding capacity, drainage, CEC, ability to store plant nutrients, shrink-swell potential, and ease of cultivation.

Sand

• Low total water holding capacity

• High (fast) Drainage

• Low Cation exchange capacity

• Very low shrink swell-potential

• High (Easy) ease of cultivation

Silt

• Moderate total water holding capacity

• Slow - moderate drainage

• Low - moderate cation exchange capacity

• low shrink swell capacity

• Moderate ease of cultivation

Clay

• high total water holding capacity

• High cation exchange capacity

• Mod. - very high shrink-swell potential

• Low (Difficult) ease of cultivation

What is CEC? What does it measure?

Cation Exchange Capacity, the amount of exchangeable cations a soil can sustain

How does pH affect nutrient availability and soil organisms?

Plants vary in the required pH range for best growth and yields

• pH of 6 - 7 is best

• pH of 5.5 - 7 is optimal

Where do saline soils typically occur and what is the cause?

Dry regions and is a result from the accumulation of soluble salts (Na, Ca, Mg, K) that dissolve in water

List the 17 essential elements needed for plant growth and their symbol.

C = Carbon

H = Hydrogen

O = Oxygen

N = Nitrogen

P = Phosphorus

K = Potassium

Ca = Calcium

Mg = Magnesium

S = Sulfur

Fe = Iron

Mn = Manganese

Cu = Copper

Zn = Zinc

B = Boron

Mo = Molybdenum

Cl = Chlorine

Ni = Nickel

What is the best way to determine nutrient availability in a specific soil? Briefly describe how to collect a soil sample.

Soil testing

Know the phrase, “Don’t guess, ____ ____.”

Soil test

What are the differences between organic and inorganic fertilizers?

Organic = derived from living matter and contains carbon

Inorganic = Synthetic or mined elements, no carbon

List and describe the 3 types of organic fertilizers.

1. Animal manures

2. Compost

3. Green manures

What is fertilizer analysis or grade?

• Where is it displayed? Why is it displayed? How is it displayed? (hint - ratio)

Amount of nutrients contained in a commercial fertilizer

• Must be displayed on label

• For consumer protection

• Must include N-P-K (20-10-5)

List and briefly describe the six different fertilization methods.

1. Broadcast = Applied evenly across the entire area

2. Injection = Water soluble liquids (or gases) placed under soil surface near roots

3. Banding = applied at planting within 2” of the row

4. Popup fertilizers = placed IN the seedbed with the seed

5. Side-dressing = placed alongside the row (mid-season)

6. Fertigation = injecting the fertilizer in the irrigation water

List 6 best nutrient management practices

1. Test soil regularly

2. Test manure before application

3. Time fertilizer and manure application to crop needs

4. Use the most efficient method for fertilizer application

5. Combine nutrient management with the soil conservation

6. management

7. Incorporate green manures, cover crops, and perennials into rotations

What is soil erosion and what are four ways to reduce its effects?

Accelerated loss of soil through the action of wind or water

1. Crop rotations

2. Contour Stripping

3. Conservation tillage

4. Conservation Reserve Program (CRP)

What is a weed?

A plant growing where it is not wanted

What are the five methods of weed control?

1. Prevention

2. Cultural practices

3. Biological control

4. Mechanical or manual control

5. Chemical control

What are the five characteristics of weeds that allows them to thrive?

1. Large seed production

2. Long seed dormancy

3. Seed dispersal

4. Vegetative reproduction

5. They can grow anywhere

Define Critical Weed Free Period. When does it occur in the growing season?

Window of time in the growing season that weeds cause the largest reduction in yield, and must be controlled.

Occurs 4-6 weeks after crop emergence