Feedbacks in the N Cycle

Question 1

What are the 3 main forms of fertiliser?

Answer 1

• Ammonium
• Nitrate
• Urea

Question 2

When to N2O emissions peak?

Answer 2

After fertilisation and harvesting and tillage.

Question 3

What are the factors affecting activity and N fate?

Answer 3

• pH
• O2 availability
• NO3 availability

Question 4

What effect does temperature have on community structure and size of denitrifiers?

Answer 4

Community structure: minor difference until over 25.c
Community size: increased size up to 20.c (temp is not driving population size, carbon and nitrate availability is)

Question 5

What is the spatial structure of soil?

Answer 5

Macroaggregates made up of microaggregates.
Spaces filled with water or air, some pores left open for capillary action.

Question 6

What happens to soil in heavy rainfall?

Answer 6

Anaerobic, all organisms denitrifying.
Soil gets more compacted

Question 7

What is the rhizobox experiment?
What did it show?

Answer 7

Mesh box, roots don’t grow through
Added labelled 13C and 15N.
Assesses C and N pools and distance from root surface.
A line of carbon was injected into soil profile every day

More carbon = more denitrification

Question 8

How can emissions from fertiliser be reduced?

Answer 8

Balancing respirable carbon sorces with more complex forms.
Supplementing conventional fertiliser with composted fertiliser decreases N2O released.

Question 8

What does tilling do?

Answer 8

Reduces soil carbon.