Soil Organic Matter

Question 1

The largest, and fastest pathway of C flow from shoots to soil is through roots.

Answer 1

Soils contain
~ 3x the C in vegetation
~ 2x the C in the atmosphere

Question 2

Change in land-use management can capture carbon

Answer 2

Clearing peatland rainforest is very detrimental due to carbon storage in that habitat

Question 3

The belowground biomass and soil carbon loss is sometimes equal or greater than

Answer 3

aboveground biomass and soil carbon loss

Question 4

Environmental controls on soil C cycling

Answer 4

Decomposition and release of plant-available nutrients from organic molecules requires:

Moisture 
Oxygen
Moderate pH
Moderate temperatures
Active microbial populations
Decomposable organic matter

Question 5

Relief of the land

Answer 5

gradients and drainage form different soils. Peat soils form in the valleys where water pools.

Question 6

Over-grazing of the UK uplands-

Answer 6

soil compaction

and vegetation removal leads to increased soil loss

Question 7

There are over 10 000 000 000 tonnes of C in UK soils

Total UK emissions in 2008 = 170 000 000 tonnes

Answer 7

Rachel Kyte, the World Bank’s special envoy for climate change: “Carbon pricing is a necessary if insufficient first step in [a country’s] transformation toward an economy that is competitive and creating jobs, but is decarbonizing and on track for zero net emissions by the second half of the century. In other words, the World Bank wants a price on carbon.”

Question 8

East Anglian Fenlands (the Fens): 88% is cultivated – it is the largest area of Grade 1 agricultural land in the UK

Answer 8

37% of vegetable production in England comes from the Fens
Peat wastage by oxidation, compaction and shrinking is causing loss of 2.1 cm/yr - there is less than 50-100 years of cropping left!

Question 9

Litter main polymeric constituents:

1. Plant litter
   C: Cellulose, lignin
   N: Proteins, nucleic acids
   P: Nucleic acids, phospholipids

Answer 9

2. Microbial litter
   C: Polysaccharides, chitin, melanin
   N: Proteins, nucleic acids, chitin
   P: Nucleic acids, phospholipids, techoic acids

Question 10

Litter controls on decomposition rates

Answer 10

High C:N and C:P ratios lead to immobilisation instead of mineralisation

Question 11

Condensed tannins from heather leaf litter slows decomposition and increases C storage

Answer 11

Enzymes can’t bind to materials in the leaf litter therefore can’t decompose

Question 12

Humification:

Answer 12

The polymerisation and alteration of phenolic-rich organic matter into highly chemically resistant, persistent amorphous colloidal organic material
(humic acid, fulvic acid, humin).

Question 13

Land use and land management effects on soil organic carbon:

Answer 13

Inputs
Tillage methods
Land use change
Crop rotations (especially use of leys)

Question 14

Mean residence time of root C is 2.4 x that of shoot C

Answer 14

Lignin % in roots is typically 2.2 x that of shoots

Lignin/N ratio in roots is 2.4 x that of shoots

Question 15

Small inputs of C result in poor soil quality

Answer 15

Only about 5% of wheat biomass is in roots

Question 16

Bioenergy controversy

Answer 16

Straw-powered stations means it gets burnt and no Carbon returns to the Earth

Question 17

Our findings show that the avoided emissions are between 2 and 5
times greater when biochar is applied to agricultural land (2–19 Mg CO2 ha-1 y-1) than used solely for fossil energy offsets

Answer 17

. 41–64% of these emission reductions are related to the retention of C in biochar, the rest to offsetting fossil fuel use for energy, fertilizer savings, and avoided soil emissions other than CO2.

Question 18

Look up 4 per 1000

Answer 18

Minasny et al., 2017

See the papers that criticise this work and the response of the authors to the criticisms.

Question 19

Grass leys can restore arable soils

Answer 19

by increasing organic matter in them

Question 20

Statistical evidence that a higher proportion of leys in crop rotations has

Answer 20

increased the amount of carbon in arable soils in Sweden over 3 cycles of decadal surveys at over 2000 sites from 1988-2010.

Question 21

Earthworms facilitate carbon sequestration

Answer 21

through unequal amplification of carbon stabilisation compared with mineralization

Question 22

34 month ley

Increased: earthworms, pore space, water-stable aggregates (crumbs), water-holding capacity, infiltration rates, crop yields, resilience to drought & flooding.

Answer 22

Permanent arable

Soil is compact, dense, with limited pore space, has localized surface flooding, few earthworms, hard for roots to penetrate.

Question 23

Soil aggregate stability in water increases with soil organic matter

Answer 23

and earthworm population increase