Lecture 8 - Phosphorous

Question 1

3 important roles of phosphorus in organisms?

Answer 1

1) Critical constituent of phospholipid cell membranes
2) Forms the backbone of nucleic acids RNA and DNA
3) Constituent of energy forms i.e. ATP and ADP

Question 2

describe soil reserves of P in comparison to N

Answer 2

Soil reserves of P = 50% of soil reserves of N

Question 3

describe the problem of P availability

Answer 3

only a small proportion of overall P reserves are available to plants

Question 4

what 2 major pools is P found in?

Answer 4

Organic P

Inorganic P

Question 5

what is a major pathway between organic and inorganic pools?

Answer 5

microorganisms and fauna

Question 6

how do plants help drive the phosphorous cycle?

Answer 6

uptake and delivery of organic matter

Question 7

which form of phosphorus is the most mobile and why is that a problem ?

Answer 7

organic phosphorus

- easily leached out

Question 8

what causes loss of both inorganic and organic phosphorus?

Answer 8

erosion

Question 9

why does P ultimately become the element that controls productivity within systems?

Answer 9

• Running out of phosphorus is natural- natural ecosystems progressively lose P and become increasingly P limited- and their productivity declines- - Progressive natural loss

Question 10

what are the 3 phases of ecosystem retrogression?

Answer 10

1) progressive phase
2) maximal biomass phase
3) retrogressive phase

Question 11

describe the progressive phase?

Answer 11

In the early stages P is readily available through supply of ground up rocks etc when there is limited vegetation

Question 12

describe the maximal biomass phase

Answer 12

the levels of productivity builds up as vegetation grows

Question 13

what happens in the retrogressive phase?

Answer 13

eventually productivity starts to decrease

Question 14

what are the only possible things that can change the loss of P from the retrogressive phase?

Answer 14

• volcanic explosion
• dust particles from land erosion e.g. the Atlantic ocean has particularly high productivity due to dust particles that come from the Sahara desert

Question 15

what was a controversial paper about phosphorus fertiliser in the future?

Answer 15

• suggests we need to recycle human exrecement - 3 m tonnes P in pee and poo only 0.3 m tonnes returned to the land
• Do these nutrients ever go back on the land or do they just contaminate our oceans and cause eutrophication etc

Question 16

where does most of our global sanitation end up?

Answer 16

a very high proportion goes into water and not on land

• Conventional sanitation systems lead to linear flows of nutrients from agriculture, via humans, to recipient water bodies
• The valuable nutrients are rarely re-channelled back into agriculture

Question 17

what does sustainable crop production depend on?

Answer 17

sustainable nutrient supplies

Question 18

what is EcoSan?

Answer 18

• Sustainable Sanitation and Ecological Sanitation

Question 19

why is the fact phosphorus is finite a particular problem in comparison to finite fossil fuels?

Answer 19

In the case of some finite resources such as fossil fuels, alternatives can be found. There are no substitutes for phosphates
- and phosphorus is CRUCIAL

Question 20

what did a paper in 2009 state and compare this to other papers?

Answer 20

we could reach peak phosphorus production in fertiliser in 2030 - others papers say we have more available but our current use is unsustainable

Question 21

what is part of the issue about P availability?

Answer 21

the information about the availability of P is unknown - a lot of information is held by large companies and countries etc
- We need a global cooperative group to manage P stocks

Question 22

describe the advantages of using biosolids as a form of fertiliser

Answer 22

• Often performs better than inorganic fertiliser - crop yields are increased - Maize- yields are as good or better on biosolids than fertilizer

Question 23

why do biosolids sometimes work better as a fertiliser?

Answer 23

due to the extra organic matter- Increased ion exchange and water exchange capacity

Question 24

how does the use of ‘biosolids’ as a form of fertilizer have potential to reduce extent of nutrient wash out of agricultural fields?

Answer 24

• Loss of nutrients is much less than when N fertiliser is added - biosolids provide a more stable, less leachable, less polluting form of N fertilise

Question 25

what is one of the issues with biosolids and how could you maybe get around it?

Answer 25

because most of the P added in the biosolids is organic P its more mobile - see higher rates of loss - needs to be carefully managed (depends a bit on soil type etc) - could grow crops that take up more P or change tillage etc

Question 26

one issue is we dont know how biosolids effect agriculture over long time periods - describe one of the possible issues?

Answer 26

build-up of microplastics onto the land - don’t yet know exactly what this will do to the soil in the long run - how long will they stay? How do they effect organisms?
- Increased mortality and reduced growth rates have been found with increasing amounts of plastic fragments in soil

Question 27

why is england one of the best countries for adding sludges to the land?

Answer 27

due to dumping in seas being banned and our high landfill taxes, so the incentive is high to put back on land rather than burying or dumping

Question 28

Animal manure makes a significant contribution to greenhouse gas emissions and environmental pollution - how could we use it?

Answer 28

could provide biogas and fertilizer through anaerobic digestion

Question 29

what is integrated life cycle management systems?

Answer 29

• Waste is a resource, and its management should be holistic - recycling nutrients to source.

Question 30

describe a method for the integration of livestock production and waste management - and one of the probles=ms

Answer 30

• Cattle indoor housed in the winter. Reduction in carbon return to soil, but digestate easier to apply to land to recycle nutrients without pollution
• however doesnt stop methane release

Question 31

describe the strong relationship between P availability and soil PH

Answer 31

• Strong relationship between P availability and soil PH because it is tied into the availability of the other ions which bind to P - e.g. high PH = calcium phosphates - low PH = ion phosphates

Question 32

4 ways plants cope with P limitation?

Answer 32

1) Root distribution in relation to profile distributions of nutrient
2) Root morphological adaptation
3) Root biochemical activity
4) Temporal activity

Question 33

describe how plants change root distribution in relation to profile distributions of nutrient

Answer 33

• P is relatively immobile - tends to accumulate in the surface when in leaf litter
• N is more mobile so tends to penetrate down into the soil more
• Root systems have adapted to this pattern

Question 34

describe root morphological adaptations to uptake P

Answer 34

Increased surface area & proliferation
Root hairs
Mycorrhizas
Specialized roots - proteoid roots
- Roots are responsive to the nutrients
- Fungal partners of the plants can also demonstrate this
- Some specialised roots are highly proliferating
- Root hairs - particularly seen in plants that don’t form mycorrhiza

Question 35

examples of root biochemical activity

Answer 35

Phosphatases
Rhizosphere pH changes
Secretion of organic acids

Question 36

examples of temporal activity in plants in relation to P

Answer 36

• Storage of P
• Internal recycling
• Plant adaptations to increase P uptake

Question 37

how can you rejuvenate soils?

Answer 37

Phosphorus is present in small amounts in many primary (volcanic) rocks and is released slowly by weathering.

• Adding volcanic rock
• Extends the soil lifecycle
• Keeps in productive stage

Question 38

what other geological resources of P are available?

Answer 38

• Enhancing rock weathering

- Remineralisation

Question 39

what is remineralisation?

Answer 39

the utilization of natural broad elemental spectrum rock dust materials for the purpose of renewing the mineral content of soils through weathering

Question 40

what are 4 risks of large-scale rock dust fertiliser use?

Answer 40

 Energy, greenhouse gas and economic costs of rock mining and grinding.
 Health risks of silicate dusts - Possible risks from heavy metals and harmful elements and minerals.
 Potentially irreversible effects on biogeochemistry, ecosystems and soils.
 Public acceptability

Question 41

what co-benefits can the use of fast weathered basalt produce?

Answer 41

Si and trace elements, as well as generate clay (increase C storage)

Question 42

in what areas would fast weathering rock based fertiliser be useful?

Answer 42

in tropical high rainfall areas with acidic soils
e.g. Intensively weathered tropical soils like oxisols and ultisols are acidic, depleted of Ca, Mg and other base cations and silica and rich in residual iron and aluminium oxides –giving bright red colours and strong binding of the tiny remaining P reserves