Lecture 22: Mineral Nutrition - 11/29

Question 1

What additive do high agricultural yields depend on?

Answer 1

High agricultural yields depend on fertilization with mineral nutrients

Question 2

How are yields affected by addition of fertilizer?

Answer 2

For most crops, yields increase linearly until a plateau with the amount of fertilizer they absorb

Question 3

What has happened to world consumption of the primary mineral elements (NPK) over time?

Answer 3

It has climbed, from 30 million metric tons in 1960 to over 200 million metric tons currently

Question 4

About how much energy does the production, distribution, and application of nitrogen fertilizers take up in agriculture?

Answer 4

Over half

Question 5

What are the 6 macronutrients?

Answer 5

Nitrogen
Phosphorus
Potassium
Calcium
Magnesium
Sulfur

Question 6

Micronutrients (also known as trace/minor elements)

Answer 6

Necessary for plants in very small quantities

Question 7

What is the NH4+ (ammonium) to NO3- (nitrate) balance determined by?

Answer 7

pH

Question 8

Cation Exchange Capacity (CEC)

Answer 8

The ability of soil to retain, attract, and exchange cations

Question 9

Are cations or anions susceptible to water leaching?

Answer 9

Cations are not susceptible to water leaching, whereas anions are

Question 10

Nitrogen

Answer 10

A vital component of amino acids and nucleic acids.

The most frequently deficient element in crop production

Too much nitrogen can cause excessive vegetative growth and delay flowering/fruiting

Question 11

Atmospheric nitrogen

Answer 11

Not available to plants until it is fixed

Question 12

Different forms of nitrogen

Answer 12

Nitrogen gas (N2), ammonia (NH3), ammonium (NH4+), nitrate (NO3-), nitrite (NO2-), organic nitrogen (various compounds such as amino acids)

Organic nitrogen must undergo mineralization before it is accessible to plants

Question 13

Mineralization

Answer 13

The process by which chemicals present in organic matter are decomposed or oxidized into easily available forms to plants

Question 14

Which forms of nitrogen are available to plants?

Answer 14

Ammonium (NH4+) and nitrate (NO3-)

Question 15

Nitrification

Answer 15

A microbial process by which compounds are oxidized to nitrite and nitrate. Most effective in neutral soils

Question 16

What are some problems associated with nitrification?

Answer 16

1) NO3- is easily leached
2) anaerobic bacteria in waterlogged soils can cause denitrification
3) nitrification bacteria are less abundant in acidic soils

Question 17

Industrial fixation

Answer 17

Synthesis of ammonia from atmospheric N2

Question 18

What are the relative proportions of the processes that result in the natural fixation of nitrogen?

Answer 18

~10% comes from lightning and photochemical reactions
~90% comes from biological fixation

Question 19

How does symbiotic N fixation occur?

Answer 19

Bacteria associate with plant roots by forming nodules, providing them with nitrogen in exchange for carbohydrates

Question 20

What is one genus of symbiotic bacteria that helps fix nitrogen?

Answer 20

Rhizobium

Question 21

Nitrogenase

Answer 21

An enzyme that carries out the reduction of nitrogen to ammonia, which is immediately converted to ammonium

To do this, a large amount of energy is required

Question 22

What does nitrogenase need to function?

Answer 22

An anaerobic environment

Question 23

Phosphorus (P)

Answer 23

Needed in compounds involved in energy storage, membranes, and DNA/RNA

Only a small amount of P is available to a plant at a given time

Question 24

Potassium (K)

Answer 24

Helps regulate osmotic pressure and activates many enzymes involved in photosynthesis and respiration

Soils contain more K than N/P, but it is in relatively unavailable forms

Question 25

Calcium (Ca)

Answer 25

Role in cell walls and in signal transduction cascades

Question 25

Magnesium (Mg)

Answer 25

Part of the chlorophyll molecule and activates some enzymes in photosynthesis and respiration

Question 26

Sulfur (S)

Answer 26

Part of some amino acids and pungent compounds

Can be used as a fungicide

Question 27

Iron (Fe)

Answer 27

Involved in respiration and photosynthesis (in electron transport systems)

The availability of this micronutrient depends on soil pH