Soil Fertility Final Exam

Primary Macro Nutrient

N, P, K

Identify 2 forms of phosphorus taken up by plants

HPO4 -2 & H2PO4-

At pH<6.5, phosphorus forms secondary minerals causing phosphorus to become less available. What are the phosphorus two minerals formed at pH<6.5?

Fe & Al

Potassium fixation is the term for K+ trapped between the layers of certain clays. What type of clays trap the K+?

2:1 illite clays

Magnesium

Mg 2+

Sulfur

SO4 2-

Zinc

Zn 2+

Copper

Cu 2+

Explain in detail, biological, symbiotic N2 fixation. Be sure to include what happens, where it happens, organisms involved, and how it happens.

In plants, such as legumes, nodules form on the roots called rhibisomes. They absorb N2 from the air and soil and convert it to NH4, for plants to be able to use.

Agrotain

Slows down volatilization after nitrogen is on the surface. It's a urease inhibitor.

What is the manufacturing process called whereby N2 is converted to NH3?

Haber Bosh

What is the original source of most fertilizer P

Rock Phosphate

What is the most essential function of potassium in plants?

Regulation of osmosis

Explain why band placement of P is often important, especially in no-tillage management.

P is not very mobile in the soil, so it needs to be placed at the roots by band placement.

Major mechanism

N: Mass Flow

P: Diffusion

K: Diffusion

In order to make ammonium sulfate, ammonia is combined with sulfuric acid. Describe how urea is made, specifically detailing what two components are combined in order to make it.

CO2 is combined with NH3

The corn germinates and turns yellow even though weather conditions were warm and dry, with optimum soil moisture. Plant tissue analysis shows low NO3 levels. Whats happened?

Immobilization. The microorganisms absorbed the N before the plant could take it up.

You see K deficiency symptoms on the older (lower) leaves first. Why?

K is mobile in the plant. The new growth takes the K from the older leaves, therefore, you will be able to see the deficiency symptoms on the older leaves first.

What does symbiotic N2 fixation occur in?

Legumes

What is the name of the genus of bacteria that performs the N fixation process in this family of plants?

Rhizobium

There are many loss mechanism for nitrogen (loss from the soil N cycle). Which loss mechanism/process is of most concern related to the hypoxic zone in the Gulf of Mexico?

Run-Off

Distinguish (explain the difference) between absorption and adsorption.

Absorption: Substance is dissolved by liquid or solid.

Adsorption: Substance attaches to another.

Nitrification is a two-step process. What two microorganisms are responsible for this process of nitrification?

Nitrosomas

Nitrobactor

If K is so abundant in the soil already (about 0.1% or 2000 lbs/acre), why do we need to apply K as fertilizer?

Tied up in micas & feldspar

What is the main function of N in plants?

Proteins

Explain the issues needing to be considered when applying urea fertilizer (be sure to include how and why N can be easily lost from urea specifically.

Issue needing to be considered: volatilization. If the urea is not worked in or watered, agrotain should be applied to slow the process of volatilization.

What are the top two most concentrated ions on the cation exchange sites?

Ca & Mg

List the 3 criteria that must be met for a nutrient to be considered an ESSENTIAL plant nutrient.

1) Cannot replace nutrient with different nutrient.

2)Needed to complete life cycle.

3) Needed for metabolic process.

Explain the Law of the Minimum

Liebig "The most limiting factor determines yield potential".

There are three generally 3 ways in which nutrients reach the plant root surface. One is root interception. Name the other two and describe the mechanism (how it happens).

Diffusion: movement from a higher concentration to a lower concentration.

Mass Flow: Mass intake of nutrients through the roots by the intake of water.

Circle all of the components that actually do the neutralizing.

CO3 2-

A highly buffered soil will need more lime to raise the soil pH than one that is less buffered. What are the two main components in the soil that contribute to a high buffering capacity?

Organic Matter

Soil Clay Content

What is the general desired soil pH range for most of our row crops here in AR?

The general desired soil pH range for most of our row crops is 6-7.

Why is pH range required?

Different crops require different pH's. If the pH is too high or to low then the crop can't take up the nutrients it needs.

Define base saturation

Base saturation is the total % of CEC occupied by basic cations. High base saturation means that the plant is getting a larger amount of basic cations which is good because there are essential nutrients.

LIST 4 factors that contribute to/cause acidity in soil (what makes soils become acidic over time)?

A) Leaching

B) Precipitation

C) Soil organic matter decomposition

D) N and S fertilizers

Factors affecting crop yield potential are generally categorized into climatic, soil, and crop factors. List 3 factors in each category.

Climatic: Humidity, Temperature, Wind

Soil: CEC, Base Saturation, Soil Structure

Crop: Crop Variety, Row Spacing, Pests

What other COUNTRIES of the world would you expect to have acidic soils?

Ecuador

Brazil

Lime efficiency vs. particle size

The smaller the particle size, the quicker it reacts making the lime more efficient.

Lime rate needed vs particle size

The smaller the particle size, the more efficient meaning your lime rate will not be as high since you will not have to use as much.

Relative yield vs particle size

The smaller the particle size, the more efficient, meaning higher yields.

What is the pH of water that is in equilibrium with atmospheric CO2?

5.7