SSC 341 Soil Fertility Exam 4

Explain how nutrients applied on the soil surface at planting (directly over the seed row) can be considered a subsurface application.

With irrigation, nutrients dissolve and move down the soil profile, entering the root zone. since it is applied in a narrow band over the crop row, it isn't broadly over the soil surface.

True/False

Surface application of UAN before planting is called "topdressing"

False

True/False

Soil test interpretation is the largest source of error in the soil testing system.

False

True/False

FeSO4 application to a calcareous soil would likely not correct an Fe deficiency

True

True/False

Mn deficiency will likely occur in soil with pH 7 compared to pH 5

True

True/False

Sidedressing is a surface or subsurface band application after planting

True

True/False

Factors affecting Fe, Mn, Zn, and Cu availability in soils are similar

true

True/False

Mo availability decreases with increasing pH

False

True/False

Foliar application of macronutrients is as effective as soil applications

False

True/False

Application of 20 lbs of N + K directly with the seed may cause seedling damage

True

True/False

Mn toxicity will likely occur in soil with a pH of 4.2 compared to pH 6.2

True

True/False

Potential for B deficiency increases with increasing pH

True

True/False

Subsurface band applied P is recommended on soils testing low in plant available P

True

True/False

Crop response to P applications after planting are small compared to preplant P

True

Identify two benefits of crop rotation on soil productivity.

a. Rotating high residue crops reduces soil erosion.

b. Rotating crops with different nutrient requirements balances soil nutrient content.

Broadcast N applied in no-till (high C:N residues) is not as effective as subsurface N. Why?

Soil microbes will decompose the carbon through immobilization, and they will also use any nitrogen in the soil as energy for this process, tying it up so that crops cannot use it.

Briefly describe the function of riparian buffers to reduce P loading to surface waters.

Water slows down through the buffers, and phosphorus is immobile in the soil, sticking to the same soil particles, so as those particles are picked up by rainfall, they are trapped in the buffer, and the nutrients are then absorbed by the plants instead of leaching into open bodies of water.

Increase/Decrease/No Change

for recommended fertilizer N rate:

Decreasing realistic yield expectation or yield goal

Decrease

Increase/Decrease/No Change

for recommended fertilizer N rate:

previous legume crop (vs. previous grass)

Decrease

Increase/Decrease/No Change

for recommended fertilizer N rate:

Increasing soil test P from low to high

No Change

Increase/Decrease/No Change

for recommended fertilizer N rate:

minimizing water as a limiting factor to yield potential

Increase

Increase/Decrease/No Change

for recommended fertilizer N rate:

increasing profile N content

Decrease

Increase/Decrease/No Change

for recommended fertilizer N rate:

applying NH3 vs NH4NO3

No Change

Increase/Decrease/No Change

for recommended fertilizer N rate:

Increasing soil erosion rate

Decrease

Nutrient management plans always include 4 essential components, with the most important being applying the "right" rate. What are the other 3 components?

Right time, Right Placement, Right source

Identify the 6 general nutrient placement options

1. Broadcast 2. Banding 3. Dribble 4. Subsurface Injection (Knifing) 5. Sidedressing 6. Foliar

Increase/Decrease/No Change

Salt damage to germinating seedlings

40% clay compared to 4% clay content

Decrease

Increase/Decrease/No Change

Salt damage to germinating seedlings

30" row width compared to 15"

Increase

Increase/Decrease/No Change

Salt damage to germinating seedlings

Increasing fertilizer grade (5-10-5 vs 10-20-10 at the same lb N/a)

Decrease

Increase/Decrease/No Change

Salt damage to germinating seedlings

N + K sources compared to N + P sources

Increase

Increase/Decrease/No Change

Salt damage to germinating seedlings

Pop up instead of starter application

Increase

Increase/Decrease/No Change

Salt damage to germinating seedlings

40lb/a 10-10-10 compared to 20lb/a

No Change

Define soil test critical level and how is it interpreted in determining a nutrient recommendation.

It is the soil test value where above it Does Not require nutrient application, but below requires nutrient application. Labs will compare your soil sample value to its critical level and make recommendations to get it closer to that level.

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

critical level

soil test level below which crops likely respond to added nutrients, or soil test level above which crops likely to not respond to added nutrients

relative yield

(actual yield/theoretical yield) x 100

PI, KI limit

50

ZnI, CuI, MuI, SI limit

25

soil testing - fertilizer recommendation system

soil sampling, soil analysis, interpret soil test results, provide nutrient recommendations

How to calculate waste rate needed to meet a crop N requirement

% N crop= (lb/100lb)(2000/t)=(lb N crop/t)

(t/ac)(lb N crop/t)=(lb N crop/a)(10^6lb wet/total N from report lb)(Tw/2000)=(Tw/a)(1 lb Nt/0.5lb NA)

How to calculate lbs P2O5/Tw of waste

(lb P/10^6 lb dry)(2000lb/t)=(lb P/t dry)(2.29/1)=

(lb P2O5/t dry)(DM% lb dry/1 lb wet)=lb P2O5/T wet

How to calculate lbs of P2O5/a applied in excess

(waste rate gal/a)(P2O5 avail 1st yr/1000)=(lb P2O5/a applied)

(t/a)(2000lb/t)(% P)=(lb P/a)(2.29)=lb P2O5/a

(lb P2O5/a applied)-(lb P2O5/a)= lb P2O5/a excess

How to calculate yrs to meet limit

2ppm-->20ppm= +18ppm x 10 =180ppm/49.3=3.65 yrs

micronutrient deficiency

• generally occurs in high ph calc soils

• very soluble in acid soils - can be leached in acidic sandy soil

• fe and mn can be toxic @ ph<4.8 (liming reduces toxicity)

fe, zn, mn, cu solubility is highly ph dependent

• increase ph 1 unit = decrease fe 1000 fold

• increase ph 1 unit = decrease zn, mn, cu 100 fold

how does soil om improve micronutrient availability in high ph soils

• natural org compounds CHELATE or micronutrient compounds, meaning that they now cannot participate in precipitation rxns

• OM is an important source of micronutrients (min)

• high OM (>30%)can bind micronutrients causing deficiency

environmental effects

• low soil temp reduces OM min

• cool wet spring enhances zn deficiency (reduced microbial activity, root growth, and diffusion)