Lecture 6 - organic matter

Question 1

Decomposition and release of plant-available nutrients from organic molecules requires what 6 things?

Answer 1

1. Moisture
2. Oxygen
3. Moderate pH
4. Moderate temperatures
5. Active microbial populations
6. Decomposable organic matter

Question 2

describe the importance of peatlands

Answer 2

Peatlands cover < 3% of the Earth’s land surface but contain > than one third of the global soil C and soil N

Question 3

what is Sphagnum moss?

Answer 3

• a component of peatlands rich in phenolic acids, has high C:N ratios and traps water forming anaerobic bogs and mires

Question 4

describe decomposition and high altitude and high latitude environments?

Answer 4

decomposition and nutrient cycling is slow

Question 5

where is global warming faster than average?

Answer 5

in arctic regions

Question 6

what is a negative effect of global warming despite it increasing the biomass of plants in the arctic ?

Answer 6

• likely to increase carbon loss from soils

Question 7

why is thawing of permafrost bad?

Answer 7

and thawing permafrost potentially increasing CO2 and CH4 release - permafrost is very important carbon storage (long term stocks) but it requires very cold temperatures

Question 8

where is high soil carbon associated with in the UK? (5)

Answer 8

• Upland areas with high rainfall and low temperatures
• Often very acid conditions
• Waterlogging common
• Microbial populations have low activity
• Litter very chemically resistant to decay

Question 9

how do different soil types form?

Answer 9

The way different soil types form is a result of the climate and topography of the land

Question 10

describe uk carbon stocks

Answer 10

• Organic carbon is depleted under most arable land and rotational grasslands
• Current management is resulting in massive carbon losses - peatlands are becoming drained and used for agriculture
• might need a carbon tax as an incentive for farmers to keep carbon in the soil

Question 11

what are the main components of plant and microbial litter?

Answer 11

C, N, P

Question 12

what does litter have control on?

Answer 12

decomposition rates

Question 13

what effect does nutrient status have on decomposition rates?

Answer 13

preferential decay of substrates rich in nutrients (N&P)

Question 14

what reduces the rate of decomposition?

Answer 14

tannins (Protein-binding phenolic acids)

Question 15

what is humification?

Answer 15

• The polymerisation and alteration of phenolic-rich organic matter into highly chemically resistant, persistent amorphous colloidal organic material

Question 16

Land use and land management effect soil organic carbon, what inputs are important?

Answer 16

1) root litter inputs

2) C inputs

Question 17

why is root litter important?

Answer 17

• roots have high carbon residence time

- roots have high lignin and nitrogen %

Question 18

what effects C inputs?

Answer 18

• Crop residue removal impacts on soil productivity and environmental quality

Question 19

techniques to restore carbon in the soil?

Answer 19

1) addition of straw

2) adding bio char

Question 20

how does bio char work?

Answer 20

a new method to slow down the rate of decay when putting carbon back into the soils
- also offsets fossil fuel use

Question 21

apart from inputs what other management’s help protect soil organic carbon?

Answer 21

1) tillage methods
2) land use change e.g.- Reduce the amount of arable land and change it to grassland
- Grasslands hold ore carbon than arable
3) crop rotations e.g. use of leys

Question 22

what are the positive effects of leys?

Answer 22

• increase the amount of carbon in the soil

- increase earthworm populations