Plant mineral nutrition

Question 1

What are the macronutrients for plants?

Answer 1

Nitrogen, Potassium, Calcium, Magnesium, Phosphorous, Sulfur, Silicon

Question 2

What are the micronutrients for plants?

Answer 2

Chlorine, iron, Boron, Manganese, Sodium, Zinc, Copper, Nickel, Molybdenum

Question 3

Where do mobile elements show symptoms first?

Answer 3

Older leaves

Question 4

Where do immobile elements show symptoms first?

Answer 4

New growth

Question 5

What is the typical condition of Aussie soils?

Answer 5

• Old
• salty
• acidic
• leached of nutrients
• low in organic matter

Question 6

Common macronutrient deficiencies of Aus soils?

Answer 6

Nitrogen, potassium, phosphorus (NPK)
+ calcium and magnesium

Question 7

Common micronutrient deficiencies of Aus soils?

Answer 7

Iron, boron, zinc and molybdenum

Question 8

What does nitrogen deficiency present as? Treatment?

Answer 8

Yellowing/chlorosis beginning in older leaves.

Organic: any product of a living organism: compost, manure, abattoir waste
Inorganic: urea

Question 9

What does phosphorus deficiency present as? Treatment?

Answer 9

Dark green/purple malformed leaves with dead spots (necrosis), appearing on older leaves first.

Organic: guano (or chicken manure)
Inorganic: Calcium phosphate

Question 10

What does Potassium deficiency present as? Treatment?

Answer 10

Mottled or marginal (on the leaf edge) chlorosis/yellowing, occuring in older leaves first. Browning and curling of leaf tips and margins can occur after more time.

Organic: potash (potassium carbonate)
Inorganic: potassium nitrate

Question 11

What does Calcium deficiency present as? Treatment?

Answer 11

Necrosis on new leaves, root tips, fruit, meristem may die.

Organic: blood & bone, dolomite
Inorganic: Lime

Question 12

What does Magnesium deficiency present as? Treatment?

Answer 12

Interveinal chlorosis (yellowing) appearing on lower/older leaves first.

Organic: dolomite
Inorganic: Epsom salts

Question 13

What does Iron deficiency present as? Treatment?

Answer 13

Interveinal chlorosis (yellowing) appearing on younger leaves first.

Organic: Blood and Bone to maintain a prime pH <8
Inorganic: Iron chelate

Question 14

What does Boron deficiency present as? Treatment?

Answer 14

Typically necrosis/browning in any newly formed organ, appearing on younger leaves and fruits.

Organic: maintain pH < 7
Inorganic: borax

Question 15

What does Zinc deficiency present as? Treatment?

Answer 15

Chlorosis followed by necrosis, puckered leaf margins and short internodes. Symptoms appear first on younger leaves.

Organic: manure
Inorganic: zinc sulphate

Question 16

What does Molybdenum deficiency present as? Treatment?

Answer 16

Only a small amount required but some soils are deficient. Displays as interveinal chlorosis and necrosis in older leaves first.
May cause nitrogen deficiency – unable to reduce nitrate to ammonium.

Organic: manure, keep pH > 6
Inorganic: Sodium molybdate

Question 17

What are the 3 main causes of nutrient deficiency?

Answer 17

• Soil may be naturally low in particular nutrients.
• fertilizer imbalance, e.g. applying only NKP & not replacing other minerals.
• pH, as this affects different nutrient’s solubility

Question 18

Which charge are soil particles normally?

Answer 18

Negatively charged.

Question 19

What is Field Capacity?

Answer 19

the level of water that a soil can hold after gravity has assisted drainage.

Question 20

What is permanent wilting point?

Answer 20

the amount of water remaining in the soil after irreversible wilting occurs.

Question 21

What is CEC? Cation Exchange Capacity?

Answer 21

Ability of soils to hold and release cations is referred to as cation exchange capacity
One cation is released by exchange for another
Clay soils have small particles with high surface area → high CEC

Question 22

What are the 3 principal stages of the Nitrogen cycle?

Answer 22

1. Ammonification
2. Nitrification
3. Assimilation

Question 23

Describe ammonification.

Answer 23

– Majority of soil nitrogen derived from dead organic material
– Soil-dwelling saprophytic bacteria
–Incorporate nitrogen into amino acids and release excess nitrogen in the form of ammonium ions (NH4+)
– In some systems the ammonium ion is not oxidised and can be taken up by the plant
– Otherwise the ammonium ion is converted to nitrate by nitrification

Question 24

Describe Nitrification.

Answer 24

The oxidation of ammonia or ammonium ions

Performed by soil bacteria and is an energy yielding process allowing the reduction of carbon dioxide (similar to the use of light in photosynthesis)

Question 25

What is dentrification?

Answer 25

Nitrate is reduced to volatile forms of nitrogen such as nitrous oxide.
Occurs more in waterlogged soils as driven by anaerobic conditions.

Question 26

How does Nitrogen get fixed by biological processes?

Answer 26

Symbiotic bacteria such as rhizobia on legumes are nitrogen fixing with plant roots.
Free-living bacteria such as cyanobacteria can also perform this.

Question 27

How is Nitrogen transported around the plant?

Answer 27

As amino acids in phloem.

Question 28

What are the sources of sulphur?

Answer 28

Weathered rocks
Volcanic or fossil fuels release
Rain in areas with high atmospheric sulphur dioxide

Question 29

What three criteria define an essential nutrient/element for a plant?

Answer 29

• Required for a plant to complete life cycle
• Clear physiological role
• Plants display a clear symptom if deficient