Soil Science Final Exam (question submissions)

Explain the difference between absorb and adsorb in soil chemistry.

Absorb = taken into roots; Adsorb = stick onto soil particle surfaces

Discuss how cation exchange capacity (CEC) and soil pH interact to influence nutrient availability and fertilizer management strategies.

CEC determines nutrient retention, while soil pH modifies nutrient solubility. Near-neutral pH maximizes macronutrient uptake, acidic soils increase micronutrient solubility but risk toxicities. Liming raises pH and increases CEC, improving nutrient retention and reducing toxicity. Fertilizer strategies must balance both CEC and pH.

Why should we test soils? 

To determine nutrient deficiencies, to create an economically efficient fertilizer program, to avoid environmental problems from fertilizing, and to avoid other nutrient deficiencies 

Explain how root growth interacts with soil pore spaces. What are the ecological and agricultural consequences of soil compaction?

Roots grow through pores to access water and nutrients. Compaction reduces pore space, limiting root spread, water infiltration, and aeration. This leads to stunted plant growth, reduced yields, and ecosystem stress.

Discuss the causes and consequences of soil degradation globally. How do erosion, desertification, and salinization affect food security and ecosystem stability?

Soil degradation results from erosion, desertification, and chemical changes like salinization. These processes reduce fertility, limit water retention, and destabilize ecosystems. Globally, degraded soils threaten food security by lowering crop yields and increase vulnerability to climate change

What are the 4 nutrient pools?

Soil minerals (long-term reserve), Organic matter (intermediate to long-term), Adsorbed nutrients (readily available), Dissolved ions (immediately available)

What is the difference between saline and sodic soils?

Saline soils have a high concentration of soluble salts, but low levels of sodium (Na). Sodic soils have low levels of soluble salts, but a high concentration of sodium (Na).

At which nutrient level are yields at their highest?
A. Level I - Deficient   B. Level II - Sufficient   C. Level III - High   D. Level IV - Toxic 

c

What are the three sizes of soil particles?

Sand (largest), Silt (medium), Clay (small)

Why are wet soils bad for farming?

They create anaerobic conditions, which are bad for and can kill roots. They also make it hard for farmers to get into the field when they need. Drainage can help mitigate these problems.

Define Soil Fertility?

the ability of soil to supply nurtients in adequate amounts and forms for plant growth 

List two mircobial processes that slow dramatically in acidic soils?

Nitrogen fixation and nirtifixation; also OM decay slows 

Name all the nutrient levels with a small definition of each. 

Level I Deficient: Nutrient is deficient, Growth and productivity is impaired, adding missing minerals will repair 

Level II Sufficient: Critical levels are reached, plants’ needs are met, more fertilizer may increase yield slightly, but not enough to pay for fertilizer, growers may fertilize to replace nutrients lost in harvest 

Level III High: nutrient levels high and yield are at max, additional nutrients would be stored in plants (luxury consumption) 

What are the five feeding groups of soil food web role? 

Plant feeder: attach to roots 

Bacteria: feeders, graze on bacteria 

Fungi: feeders, stylet pierces fungal cells walls

Preditors: feed on protozoa and other nematods 

Entompathogenic: invades insepcts, release symbiotic factors that kill host

How does particle size affect a soil's specific surface area, as well as the number and size of it's pores (including macropores and micropores)? 

Specific surface area is the total surface area exposed by all particles in a given weight of soil. The smaller the particles, the greater the total specific surface area for the same mass. The more and small particles increase pore numbers and shift the pore size 

How Lime neutralized soil Acidity 

1- base anion: combining with hydrogen ions to form water 

2- calcium: replaces hydrogen and aluminum ions on cation exchange sites via mass action, freeing them into the soil solution, whey they are neutralized 

Why should we test Soils? 

to determine its nutrient levels, pH, and physical characteristics, which helps in making informed decisions about fertilization, amendments, and potential environmental contaminants

List 4 types of grain crops?

Answer: Corn, Barley, wheat, and soybeans

Contrast self-pollinated plants and cross-pollinated plants?

self pollinated plants - are plants that are pollinating themselves 

cross pollinated plants - plants that share the pollination

Question: What are the three types of soil colloids?

Answer: Silicate clays, Oxide clays, Humus

How does lime neutralize soil Acidity 

Answer: It combines with hydrogen ions to form water

Describe what a bucket auger does.

Bucket augers mix the soil and are best for collecting bulk samples from cohesive or compacted soils. they are most effective in dense clays, glacial tills, and firm subsoils and are ideal for fertility sampling.

what are the three types of particles in soil?

sand, silt, clay

one teaspoon of fertile soil can contain how much fungi?

450,000

What do we use to measure nutrient holding?

Cation exchange capacity 

why do we lime soles?

to neutralize acidity and restore the best soil PH 

What are the 4 soil nutrient levels

I- deficient 

II- Sufficient

III- High

IV- Toxic 

what is the difference between peds and clods?

peds are naturally occurring 

clods- are caused by tillage 

How many soil orders are there 

12

What is the difference between macronutrients and micronutrients, and give at least 3 examples of each?

Macronutrients are the nutrients that plants need in higher amounts. Primary macronutrients consist of nitrogen, phosphorus, and potassium. Secondary macronutrients consist of calcium, magnesium, and sulfur. Micronutrients are those that the plants need, but in smaller amounts. These consist of boron, copper, chlorine, iron, manganese, nickel, zinc, and molybdenum.

What three things determine what pH a soil has? What range of numbers are on the pH scale? Which are acidic and which are basic?

Soil pH is set by the interaction of soil materials, ions in solution, and cation exchange. The pH scale has a range of 0-14. Acidic things are those that are 0-7. Basic things are those that are 7-14.

List 2 reasons why you would want to test soils.

Any of the following: to determine nutrient deficiencies, to create an economically efficient fertilizer program, to avoid environmental problems from fertilizing, to avoid other nutrient deficiencies.

Soil texture is determined by _________.

The proportion of soil particles (sand, silt, and clay).

What are three ways to improve the water intake rate of the soil?

Subsoiling/deep plowing, aeration, mulching

What is the difference between macronutrients and micronutrients? Give two examples of each.

Macronutrients are needed in large amounts (Nitrogen, Phosphorus, Potassium, Calcium)

Micronutrients are needed in small amounts (Iron, Zinc, Manganese) 

Why do farmers lime soil?

• to raise pH

• reduce aluminum toxicity

• improve nutrient availability (especially phosphorus)

• support soil microbes (like Rhizobium)

• Supply Ca or Mg

What does a standard soil test typically include?

• texture

• organic matter

• pH

• Buffer pH

• Available phosphorus

• Exchangeable potassium

What are four things plants depend on soil for?

• anchorage

• oxygen

• nutrients 

• water

Describe the Mollisols soil order, including whether they are suitable for agricultural use.

• Mollisols are dark rich agriculture soils that have deep A horizons and have low to moderate rainfall and the best for agriculture use and are found in grasslands and make up 25% of U.S. soils.

What are 3 macronutrients that soils need to thrive?

Nitrogen, Potassium, Phosphorus, Calcium, Magnesium, and Sulfur.

Describe where neutral, acids, and bases are on the soil PH scale.

The scale is 0-14 and Acids are 0-<7, bases are >7-14, and neutral is 7.

What are the four levels of soils testing and which is the best for agriculture?

Deficient, sufficient, high, and toxic. High is best because it brings max yields.

What are the three types of rock?

Sedimentary, igneous, and metamorphic rocks.

Describe how tilling agricultural land can degrade your soil profile.

Tilling can lead to tillage pans building up over time, the loss of valuable nutrients in the topsoil, the loss of root zones and biological life, and more. It is better to practice no till, cover crops or other methods to prevent these issues.

What is Cation Exchange Capacity?

Answer: Total negative charge sites available to hold cations. Controlled by amount of clay, type of clay, and amount of humus.

What are three ways to manage salted soils?

Answer: Use high-quality irrigation water, keep soil moist, over-irrigate enough to leach salts out of root zones, avoid overfertilization, maintain a good soil-testing program, plant on ridge shoulders in furrow-irrigated fields, use drip irrigation.

How often should you test annual field crops?

2-3 years

What are the five key soil-forming factors?

Answer: Parent material, Climate, Life, Topography, Time.

What are mycorrhizae and how are they important?

Answer: Fungi that act in symbiosis with plant roots. Uses roots to obtain food/nutrients. Increases phosphorus, zinc, and copper uptake, increases water absorption. Plants use these because they are cheaper to build than roots.

True or False

Charged colloids usually carry a negative charge that attracts cations
from the soil solution

True?

What sets soil pH

Interaction of soil minerals

Ions in solution

Cation exchange

How are soil samples taken?

Soil samples can be taken by using multiple differnt types of tools such as soil tubes, augers, and spades. You must make sure that there is no organic material in your sample and that you take a full sample per location. Then the samples can be sent to labs to determine the quality and nutrition of the soil.

How is soil textured determined?

By the soil particles sand, silt, and clay

Chapter 10: What is the Cation Exchange Capacity (CEC), and what factors influence CEC?

CEC is how we measure the "nutrient" holding capacity - it is the total negative exchange sites to hold cations. The amount of clay, type of clay, and amount of humus control the soil CEC

Chapter 11: What happens to soil biota in acidic soils, and what processes are affected?

Most organisms prefer neutral soils, so they die off in areas of higher acidity. Due to the impact on microbes, nitrogen fixation decreases, nitrification decreases, and organic matter decay slows

Comprehensive #1 (Chapter 8): What factors affect water infiltration in soil?

Texture & structure, organic matter level, compaction, barriers present (hardpans, plow pans), slope (steeper = more runoff, less infiltration)

Comprehensive #2 (Chapter 6): What are the three components of organic matter?

Living biota - roots, microbes, other organisms

Fresh/decaying residues - fallen leaves, dead organisms, animal excrement, crop residues, 

Humus - residues of active decay; stable organic compounds remaining in the soil

What are the pros and cons to cropland drainage? - 

• Pros: earlier field entry and reduced disease 

• Cons: Costly and OM loss 

List some ag practices that promote carbon loss 

• burning crops

• soil erosion

• tillage

• conversion of land from pasture to tilled land 

• removal of plant/crop residue 

What is the definition of monoculture? 

• growing a single crop in a field during growing season

There are 25 primary crops in the US, what 4 make up more than 1/2 of the cropland in the US?

• Corn, soybeans, wheat and hay

What is Dry matter? 

- weight of all components of plant without water. Changes with developmental stages. 

Q: What is the Anion Exchange Capacity (AEC)? 

     A: It is the ability of soil to retain and exchange anions such as nitrate, phosphate, sulfate, and chloride. It is highest in acid soils that are rich in oxide clays

Q: What are four factors affecting

     A: Cation Exchange Capacity, Soil Texture, Type of Clay, Organic Matter

Q: What does standard series soil testing typically include?

      A: Texture, Measure of Organic Matter, pH and buffer pH, Available phosphorus, Exchangeable potassium

Q: What is the difference between Adhesion and Cohesion with soil?

     A: Adhesion- attraction of water to soil particles (holds films on particle surfaces)

Cohesion- attraction of water to water (holds the water column together)

Q: What are the five key soil forming factors?

     A: Parent material (broken rock), climate, life, topography, time, and human activity

What is Soil Fertility?

The ability of the soil to supply nutrients for plant growth  

What are The Four Factors that determine Lime Requirement?

Present soil pH

2. Desired Target pH

3. Soil buffering capacity 

4. Type of liming material used 

Three soil sampling tools.

Soil probe, Soil augur, and common spade.

What are the four types of flow in water movement and describe them. 

Gravitational flow- water movement driven by gravity in the soil in a downward direction in the Earth's gravitational field.

Saturated flow- water movement in the soil when all pores are filled with liquid water.

Unsaturated flow- water movement through the soil when the largest pores are not filled with water.

Vapor Flow- Dominates when liquid films are 5 or fewer molecules thick, water is tightly adsorbed.  

What pH levels are good for most crops in mineral soils and in organic soils?

The optimum pH levels for most crops in mineral soils are 6 to 7 while in organic soils are 5.5 to 6.5.

What are some reasons on why people test soil?

Some reasons are to identify nutrient deficiencies, create a economically efficient fertilizer program, avoid environmental problems from fertilizer, and avoid other nutrient deficiencies.

Briefly explain how mycorrhizae fungi helps a plant.

Hyphae stands extend into the root system practically becoming apart of it and are able to get into tiny pores that the roots would otherwise not be able to access. They are less taxing for the plant to build compared to actual roots and are highly efficient in what they do. They help increase water absorption, rootlets live longer, and phosphorous uptake is greatly enhanced.

What are the 3 requirements for land to be legally classified as a wetland?

Hydric soils, which is soils that are wet enough for anaerobic conditions near the surface. Wetland hydrology, which is measured saturation during the growing season. The presence of wetland vegetation.

What controls which cations are absorbed? 

A: Relative bonding strength. The general order of decreasing adsorption strength is as follows: – Al³⁺ > H⁺ > Ca²⁺ > Mg²⁺ > K⁺ = NH₄⁺ > Na

Q: What damage occurs when sodium ions saturate cation exchange sites?

A: Soil colloids disperse, breaking up soil aggregates. This decreases the soil's structure and stability, allowing fine particles to clog pores and restrict water movement and infiltration. 

Q: What are two things to ensure when collecting samples randomly across a field?

A: Avoid areas 100–300 ft near roads, barns, fences, dead furrows, fertilizer spills, or unusual spots, and aim for 15+ subsamples in large areas.

Q: What drives soil aggregation?

A: Microbes (Especially fungi and actinomycetes).

Q: What are the 3 indicators of poor drainage in a soil?

A: Standing water persists several days after rain, presence of water-loving plants, and a percolation test (filling pre-wetted holes with water and recording the drain time to infer drainage rate).