Soil Organic Matter Flashcards
The largest, and fastest pathway of C flow from shoots to soil is through roots.
Soils contain
~ 3x the C in vegetation
~ 2x the C in the atmosphere
Change in land-use management can capture carbon
Clearing peatland rainforest is very detrimental due to carbon storage in that habitat
The belowground biomass and soil carbon loss is sometimes equal or greater than
aboveground biomass and soil carbon loss
Environmental controls on soil C cycling
Decomposition and release of plant-available nutrients from organic molecules requires:
Moisture Oxygen Moderate pH Moderate temperatures Active microbial populations Decomposable organic matter
Relief of the land
gradients and drainage form different soils. Peat soils form in the valleys where water pools.
Over-grazing of the UK uplands-
soil compaction
and vegetation removal leads to increased soil loss
There are over 10 000 000 000 tonnes of C in UK soils
Total UK emissions in 2008 = 170 000 000 tonnes
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.”
East Anglian Fenlands (the Fens): 88% is cultivated – it is the largest area of Grade 1 agricultural land in the UK
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!
Litter main polymeric constituents:
- Plant litter
C: Cellulose, lignin
N: Proteins, nucleic acids
P: Nucleic acids, phospholipids
- Microbial litter
C: Polysaccharides, chitin, melanin
N: Proteins, nucleic acids, chitin
P: Nucleic acids, phospholipids, techoic acids
Litter controls on decomposition rates
High C:N and C:P ratios lead to immobilisation instead of mineralisation
Condensed tannins from heather leaf litter slows decomposition and increases C storage
Enzymes can’t bind to materials in the leaf litter therefore can’t decompose
Humification:
The polymerisation and alteration of phenolic-rich organic matter into highly chemically resistant, persistent amorphous colloidal organic material
(humic acid, fulvic acid, humin).
Land use and land management effects on soil organic carbon:
Inputs
Tillage methods
Land use change
Crop rotations (especially use of leys)
Mean residence time of root C is 2.4 x that of shoot C
Lignin % in roots is typically 2.2 x that of shoots
Lignin/N ratio in roots is 2.4 x that of shoots
Small inputs of C result in poor soil quality
Only about 5% of wheat biomass is in roots
