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
