35. Soil

Soil and Nutrients

What is Soil (and Why is it Important)?: Crash Course Geography #17

Soil Chemistry P1

How Cation Exchange Capacity works

Plant Nutrition: Mineral Absorption | Part 1

Soil Biology, Chemistry, and Physics...Oh My!

The Living Soil Beneath Our Feet | California Academy of Sciences

Ion Exclusion

Soil Nutrients

 No. Magnesium is not a component of nucleic acids. 

 No. Manganese is not a component of nucleic acids. 

 No. Iron is not a component of nucleic acids. 

 No. Sulfur is not a component of nucleic acids. 

Consider which of these nutrients is a component of nucleic acids.

If a plant is deficient in __________, it will not be able to make DNA.

 Branch extensively so as to maximize the ability to absorb whatever nitrates are available 

 No. The response of the roots to low nitrate availability is just the opposite. 

 Produce additional proteins for transporting and assimilating the available nitrates 

 No. This is a response in areas high in nitrates. 

 Produce additional root hairs to facilitate nitrate absorption 

 No. Root hairs increase the surface area available for water absorption. 

 Increase mycorrhizal associations so as to increase nitrate absorption 

 No. Mycorrhizae increase surface area for water absorption. 

Plants require nitrates to survive and thrive.

How might roots react when they encounter a region of the soil that is low in nitrates?

 No. Magnesium is a macronutrient obtained from the soil. 

No. Nitrogen is a macronutrient that is made available to plants by bacteria in the form of ammonium (NH4+) or nitrate (NO3&ndash;) in the soil.

 No. In general, water is obtained from the soil. 

 All of the listed responses are correct. 

 No. Only one of the choices is correct. 

Some of these substances will come from the soil.

Which of the following substances does a plant obtain from the air?

A mineral deficiency is likely to affect older leaves more than younger leaves if
a. the mineral is a micronutrient.
b. the mineral is very mobile within the plant.
c. the mineral is required for chlorophyll synthesis.
d. the mineral is a macronutrient.

Soil and Soil Dynamics

Cation Exchange

Micronutrients are needed in very small amounts because
a. most of them are mobile in the plant.
b. most serve mainly as cofactors of enzymes.
c. most are supplied in large enough quantities in seeds.
d. they play only a minor role in the growth and health of the plant.

 To test whether an element is essential to a certain species of plant 

 No. This is a goal of growing plants in a hydroponic culture. 

 To grow crops such as alfalfa and wheat that provide good ground cover 

 No. This is a method of slowing down erosion, but it is not related to phytoremediation. 

 To increase resistance to aluminum toxicity 

 No. This is a goal of genetic modification. 

 To clean contaminated sites by using plants that have the ability to extract and store soil pollutants 

Consider that phytoremediation is a type of bioremediation.

What is the goal of phytoremediation?

The inorganic nutrient most often lacking in crops is
a. carbon.
b. nitrogen.
c. phosphorus.
d. potassium.

Plant Nutrition: Mineral Absorption | Part 3

 The citric acid produced by the plant dissolved the aluminum in the soil. 

 No. This is not the mechanism that increased aluminum tolerance. 

 The citric acid produced by the plant coated the root tips and blocked the entrance of aluminum. 

 The citric acid produced by the plant degraded the aluminum so that the plants couldn't take it up. 

 No. Citric acid is not capable of degrading aluminum. 

 No. Only one of the other choices is correct. 

 The citric acid produced by the plants bound the free aluminum in the soil, making it less available to be taken up by the plants. 

How might a change in pH change the bioavailability of a particular substance?

How did the addition of a gene for citrate synthesis increase the tolerance of tobacco and papaya plants to high aluminum concentrations in the soil?

 No. Copper does not play a major role in chlorophyll formation. 

 No. Molybdenum does not play a major role in chlorophyll formation. 

 No. Sulfur does not play a major role in chlorophyll formation. 

 No. Phosphorus does not play a major role in chlorophyll formation. 

Which mineral deficiencies may lead to chlorosis?

If a plant's leaves are yellowing, it may be that the plant is deficient in the elements needed to make chlorophyll, one of which is __________.

 are composed of nitrogen needed by plants 

 No. Roots do not absorb soil particles. 

 eliminate spaces for air and facilitate drainage 

 No. The elimination of air spaces would not facilitate drainage. 

 fill spaces and keep oxygen out of the soil 

 No. The arrangement of soil particles creates air spaces within the soil. 

 No. Humus is formed by the action of decomposers such as fungi. 

 are charged and hold ions needed by plants 

Think about the structure of the soil.

The particles in soil are important because they __________.

Two groups of tomatoes were grown under laboratory conditions, one with humus added to the soil and one a control without humus. The leaves of the plants grown without humus were yellowish (less green) compared with those of the plants grown in humus-enriched soil. The best explanation is that
a. the healthy plants used the food in the decomposing leaves of the humus for energy to make chlorophyll.
b. the humus made the soil more loosely packed, so water penetrated more easily to the roots.
c. the humus contained minerals such as magnesium and iron needed for the synthesis of chlorophyll.
d. the heat released by the decomposing leaves of the humus caused more rapid growth and chlorophyll synthesis.

DRAW IT Draw a simple sketch of cation exchange, showing a root hair, a soil particle with anions, and a hydrogen ion displacing a mineral cation.

Nutrient Cycling | Soil Food Web School

Why is it important for plants to exclude certain ions? Summarize the difference between active and passive exclusion mechanisms.

In a semester-long experiment tracking growth in plants, your lab partner—who often skips class—carefully records the mass of water added to a potted plant with the expectation that this addition will be fully accounted for in the mass gained by the plant. Is your lab partner right or wrong? Explain.

Consider the following statements regarding limiting nutrients. Select True or False for each statement.
T/F Nitrogen (N), phosphorus (P), and potassium (K) are common examples.
T/F Their presence limits the availability of micronutrients.
T/F Their availability tends to limit plant growth.
T/F Certain macronutrients and micronutrients can be considered limiting nutrients.

 No. Plants manufacture their own sugars. 

 No. Plants manufacture their own complex carbohydrates. 

 No. Plants manufacture their own organic compounds. 

Plants are autotrophs.

When you add "plant food" to your potted geraniums, what are you actually providing the plant with?

 No. Farm and garden soils are less likely to be deficient in these micronutrients than in other nutrients. 

 No. Farm and garden soils are less likely to be deficient in these nutrients than in other nutrients. 

 No. Though soil in agricultural and domestic use will become depleted of all minerals, not all minerals are depleted at the same rate, and not all essential nutrients are obtained from soil. 

Consider which of these are used up most quickly by plants.

Fertilizers are usually enriched in __________.

Soil Nutrients | From the Ground Up

The Living Soil: How Unseen Microbes Affect the Food We Eat (360 Video)

Soil Composition

 Deficiency symptoms of freely moving nutrients will show up first in younger organs. 

 No. The symptoms would show up in older organs first. 

 Deficiency symptoms of immobile nutrients will show up first in older organs. 

 No. The symptoms would show up first in young organs. 

 Symptoms of mineral deficiency always show up in older leaves first. 

 No. Mobility of the nutrient is a factor. 

 Symptoms always show up in younger leaves first. 

 Growing tissues would show signs of mineral deficiency of mobile nutrients after older tissues. 

Think about bulk transport in plants.

Which of the following is a true statement regarding mineral deficiency symptoms in plants?

 The pH level of soil affects anion exchange and influences the chemical form of minerals. 

 No. The pH level of soil affects cation exchange. 

 The pH level of soil affects water levels. 

 Plants may grow too tall if the pH is too high. 

 No. There is no one correlation between pH and plant height, some plants being adapted to lower-pH soils and others to higher-pH soils. 

 None of the listed responses is correct. 

 No. One of the other answers is correct. 

 The pH level of soil affects cation exchange and influences the chemical form of minerals. 

Consider how a change in hydrogen ion concentration could affect the chemistry of essential elements.

Why do farmers need to be concerned with the pH level of soil?

No. K+ is positively charged and is attracted to the negatively charged surfaces of soil particles.

No. Ca2+ is positively charged and is attracted to the negatively charged surfaces of soil particles.

No. Mg2+ is positively charged and is attracted to the negatively charged surfaces of soil particles.

No. NH4+ is positively charged and is attracted to the negatively charged surfaces of soil particles.

Consider which molecule or ion would be repelled by soil particles.

Soil can easily become deficient in __________ because these ions are negatively charged and do not stick to negatively charged soil particles.

 No. Aluminum toxicity is usually a problem in areas, such as the tropics, with high rainfall. This was not a major factor in the Dust Bowl. 

 the leaching of nutrients from the soil 

 No. This was not a major problem in the Dust Bowl. The soil was fertile; it just wasn't held in place. 

 subsidence caused by overpumping of aquifers for irrigation 

 No. Overpumping of aquifers was not an issue in producing Dust Bowl conditions. 

 salinization caused by poor irrigation practices 

 No. Most farmers in that area did not irrigate. 

 the removal of the native grasses that held the soil in place and planting of agricultural crops 

Were farmers planting native crops that had evolved in that area?

The American Dust Bowl of the 1930s resulted from __________.

 The toxic metals will stunt the plant's growth. 

No. Thlaspi caerulescens is a plant that can tolerate high levels of toxic metals, particularly zinc.

 The toxic metals will affect the other organisms in the soil. 

 No. This is not a drawback of the technology. This is the problem the technology is trying to solve. 

 Herbivores that eat the plant may be poisoned. 

 No. This is true, but there is more to it than that. 

 If herbivores eat the plants, carnivores that feed on the herbivores may be poisoned. 

 The third and fourth responses are correct. 

Think about biological magnification and how a high concentration of toxic metals might affect the food chain.

Phytoremediation is showing promise as a sustainable, cost-effective way to decontaminate soil and water. In the case of a hyperaccumulater such as Thlaspi caerulescens, however, what might be a drawback of the technology?

 No. The practice of flooding fields wastes water through evaporation. Because of the scarcity of fresh water, this would not be considered a sustainable practice. 

 No. Although phytoremediation is a sustainable method for detoxifying soil, it is not considered to be an agricultural practice. 

 No. Aquifers can ultimately be depleted, so draining them is not sustainable. 

 The second and third responses are correct. 

 No. The use of drip irrigation conserves water resources, but phytoremediation is a method of detoxification used on degraded soils. 

How do these practices affect crop yield and the rest of the earth over the long term?

Which of the following would be considered a sustainable agricultural practice?

 All the nutrients required for plant growth have already been found. 

 No. Not necessarily. It is quite possible that nutrients needed in trace amounts are yet to be recognized as such. 

 It is very difficult to prove that a plant needs a certain nutrient. 

 No. Carefully controlled experiments can be used to determine a plant's need for a particular nutrient. This is particularly true of nutrients required in very large quantities. 

 Plants need thousands of nutrients; a new one is not significant. 

 No. It appears that about 17 nutrients are essential to plants. A discovery of another essential nutrient at this time would be of major significance. 

 Plants manufacture their own macronutrients. 

 No. There are macronutrients, such as water and carbon dioxide, that plants must obtain from an outside source. 

 Any nutrient needed in large amounts (macronutrient) has probably been noted already. 

Consider the process of science.

A botanist claims to have discovered a new macronutrient required for plant growth. Most of this scientist's colleagues are skeptical of her claim. Why might they consider it unlikely?

Plant Nutrition: Mineral Absorption | Part 2

All Things SOIL TAXONOMY

Animation: How Plants Obtain Minerals from Soil

Cation Exchange Capacity

 No. Carbohydrates supplied by the plants fuel the rhizosphere. 

The organisms in the rhizosphere are not autotrophs.

What supplies the energy for most of the microorganisms in the rhizosphere?

Why are proton pumps in root-hair plasma membranes important?
a. They pump protons into cells, generating a membrane potential (voltage).
b. They allow toxins to be concentrated in vacuoles, so the toxins do not poison enzymes in the cytoplasm.
c. They set up an electrochemical gradient that makes it possible for roots to absorb cations and anions.
d. They set up the membrane voltage required for action potentials to occur.

 Cation exchange will be enhanced, causing the plants to grow faster. 

 No. Although slightly acidic soil facilitates cation exchange, low pH changes the bioavailability of certain nutrients. 

 Plant roots are eaten away by the acidic soil. 

 No. It would be a very extreme case of soil pH that could eat away at a plant's roots. 

 Absorption of negatively charged ions is enhanced, causing the plants to grow faster. 

 No. Slightly acidic soil facilitates cation exchange, not anion exchange. 

 Absorption of calcium is enhanced, but iron is unavailable. 

 No. This situation occurs at a pH of 8. 

 Toxic aluminum ions become more available, stunting the plant's growth. 

Consider the bioavailability of different ions at different pH levels.

At low soil pH levels (5 or less), what can happen?

 No. Respiration breaks down organic molecules. 

 No. Transpiration is the evaporation of water from the surface of a leaf. 

 No. Oxidation is the loss of electrons from a molecule. 

No. This is the displacement of mineral cations in the soil by H+

What kinds of molecule make up most of the structure of plant cell walls?

The biological process that produces 96% of the dry mass of a plant is called __________.

Some of the problems associated with intensive irrigation include all of the following except
a. soil salinization.
b. overfertilization.
c. land subsidence.
d. aquifer depletion.

Transportation in Plants

. A problem with intensive irrigation is
(A) overfertilization.
(B) aquifer depletion.
(C) the long-term depletion of soil oxygen.
(D) the clogging of waterways by vegetation debris.

Consider which one of these suggested answers is a micronutrient.

Soil could be deficient in any of the following nutrients. If you had to supply one of them, which would be needed in the smallest amount?

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