Nitrogen

Question 1

N only accumulates in soils as a constituent of _____ compounds.

Answer 1

Organic

Question 2

What is the essential function of N in plants?

Answer 2

Nitrogen is an essential element of all the amino acids in plant structures which are the building blocks of plant proteins, important in the growth and development of vital plant tissues and cells like the cell membranes and chlorophyll.

Nitrogen is a component of nucleic acid that forms DNA a genetic material significant in the transfer of certain crop traits and characteristics that aid in plant survival. It also helps hold the genetic code in the plant nucleus.

Chlorophyll being an organelle essential for carbohydrate formation by photosynthesis and a substance that gives the plant their green colour, nitrogen is a component in it that aids in enhancing these features.

Nitrogen is essential in plant processes such as photosynthesis. Thus, plants with sufficient nitrogen will experience high rates of photosynthesis and typically exhibit vigorous plant growth and development.

Question 3

What are the available forms of nitrogen in soils?

Answer 3

1. Ammonium NH₄⁺
2. Nitrate NO₃^-

Question 4

What % of the total N do the available forms of N constitute?

Answer 4

Around 5%

Question 5

What is the average N% of organic matter?

Answer 5

4-5%

Question 6

What are the two opposing microbiological processes that result in the production of Ammonium in the soil?

Answer 6

Mineralisation and Imobilisation

Question 7

Nitrogen can be required in considerably higher volume than other minerals. But what is the ratio of N to P & K?

Answer 7

8.5/1/6

N,P,K

Question 8

Microorganisms consume N rich OM and release some ______ as a result.

Answer 8

Ammonium Ions

Question 9

Directly conflicting with the productivity of mineralisation, some microorganisms utilize low N, OM in the soil such as peat. They then require N so use some ammonium removing it from plant use.

Answer 9

No answer, just a statement.

Question 10

There is ____ leakage of N where clippings are returned to the soil and the area is not intensively used.

Answer 10

Little

Question 11

Removal of clippings is a major drain on N supply in the form of OM.

In sports fields what is the range of N lost from the cycle in the removal of clippings?

Answer 11

80kg ha^-1 y^-1 to 300kg ha^-1 y^-1

(Kg per hectare per year)

eg

fine turf with low input fertilisation –> highly fertilised ryegrass sports field

Question 12

N mineralisation and reserves are linked to OM content.

Where OM is low nitrogen supply is likely to be?

Answer 12

Inadequate

Question 13

What form of available N is released from organic N?

Answer 13

Ammonium NH_4-

Question 14

In the soil, Ammonium is used for?

Answer 14

1. Consumption by plants and microorganisms
2. Oxidation to Nitrate

Question 15

Ammonium+ is cationic and is therefore retained in CEC sites. What are the sources of cation exchange sites?

Answer 15

Clays & Organic matter

In sandy, low clay soils. OM is the only facilitator of the CEC function.

(See Cation exchange capacity section for more)

Question 16

Ammonium is oxidised first to ____ then to _____.

Answer 16

Nitrite then to Nitrate

Question 17

Nitrification is rapid in soils of what pH?

Answer 17

Neutral

(Pace is reduced to around 10% of neutral in strongly acidic soils.)

Question 18

Nitrate is an anion. At most soil pH’s oxides of iron and aluminium are positively charged and strong acids can exchange on these sights. Name three such acids.

Answer 18

1. Nitrate
2. Sulphate
3. Chloride

Question 19

Anion exchange sites are weaker than cation sites. How?

Answer 19

The retention is very weak.

(Weaker acids such as phosphate have a much stronger covalent adsorption)

Question 20

Because of the sparse and weaker Anion exchange sites, nitrate is how many times more abundant in leaching water?

Answer 20

10-100

Question 21

Denitrification is?

Answer 21

The non-assimilatory reduction of nitrogen.

Question 22

Explain the circumstances of denitrification.

Answer 22

1. Nitrification requires molecular oxygen in well-aerated soils.
2. De-nitrifying bacteria are most active in wet, poorly aerated soils rich in OM.
3. Nitrate is reduced to nitrous oxide and nitrogen gasses.