Lecture 8 - Phosphorous Flashcards
3 important roles of phosphorus in organisms?
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
describe soil reserves of P in comparison to N
Soil reserves of P = 50% of soil reserves of N
describe the problem of P availability
only a small proportion of overall P reserves are available to plants
what 2 major pools is P found in?
Organic P
Inorganic P
what is a major pathway between organic and inorganic pools?
microorganisms and fauna
how do plants help drive the phosphorous cycle?
uptake and delivery of organic matter
which form of phosphorus is the most mobile and why is that a problem ?
organic phosphorus
- easily leached out
what causes loss of both inorganic and organic phosphorus?
erosion
why does P ultimately become the element that controls productivity within systems?
- Running out of phosphorus is natural- natural ecosystems progressively lose P and become increasingly P limited- and their productivity declines- - Progressive natural loss
what are the 3 phases of ecosystem retrogression?
1) progressive phase
2) maximal biomass phase
3) retrogressive phase
describe the progressive phase?
In the early stages P is readily available through supply of ground up rocks etc when there is limited vegetation
describe the maximal biomass phase
the levels of productivity builds up as vegetation grows
what happens in the retrogressive phase?
eventually productivity starts to decrease
what are the only possible things that can change the loss of P from the retrogressive phase?
- 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
what was a controversial paper about phosphorus fertiliser in the future?
- 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
where does most of our global sanitation end up?
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
what does sustainable crop production depend on?
sustainable nutrient supplies
what is EcoSan?
- Sustainable Sanitation and Ecological Sanitation
why is the fact phosphorus is finite a particular problem in comparison to finite fossil fuels?
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
what did a paper in 2009 state and compare this to other papers?
we could reach peak phosphorus production in fertiliser in 2030 - others papers say we have more available but our current use is unsustainable
what is part of the issue about P availability?
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
describe the advantages of using biosolids as a form of fertiliser
- Often performs better than inorganic fertiliser - crop yields are increased - Maize- yields are as good or better on biosolids than fertilizer
why do biosolids sometimes work better as a fertiliser?
due to the extra organic matter- Increased ion exchange and water exchange capacity
how does the use of ‘biosolids’ as a form of fertilizer have potential to reduce extent of nutrient wash out of agricultural fields?
- 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
what is one of the issues with biosolids and how could you maybe get around it?
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
one issue is we dont know how biosolids effect agriculture over long time periods - describe one of the possible issues?
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
why is england one of the best countries for adding sludges to the land?
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
Animal manure makes a significant contribution to greenhouse gas emissions and environmental pollution - how could we use it?
could provide biogas and fertilizer through anaerobic digestion
what is integrated life cycle management systems?
- Waste is a resource, and its management should be holistic - recycling nutrients to source.
describe a method for the integration of livestock production and waste management - and one of the probles=ms
- 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
describe the strong relationship between P availability and soil PH
- 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
4 ways plants cope with P limitation?
1) Root distribution in relation to profile distributions of nutrient
2) Root morphological adaptation
3) Root biochemical activity
4) Temporal activity
describe how plants change root distribution in relation to profile distributions of nutrient
- 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
describe root morphological adaptations to uptake P
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
examples of root biochemical activity
Phosphatases
Rhizosphere pH changes
Secretion of organic acids
examples of temporal activity in plants in relation to P
- Storage of P
- Internal recycling
- Plant adaptations to increase P uptake
how can you rejuvenate soils?
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
what other geological resources of P are available?
- Enhancing rock weathering
- Remineralisation
what is remineralisation?
the utilization of natural broad elemental spectrum rock dust materials for the purpose of renewing the mineral content of soils through weathering
what are 4 risks of large-scale rock dust fertiliser use?
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
what co-benefits can the use of fast weathered basalt produce?
Si and trace elements, as well as generate clay (increase C storage)
in what areas would fast weathering rock based fertiliser be useful?
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
