Lecture 8 Flashcards
is phosphorous finite?
yes
phosphorous required for in plants ( Small pic)
- phospholipid cell membrane
- ATP/ADP
- essential element for life
2 nutrients which limit plants growth
N & P
nitrogen dry weight in plant
1-5% of plant dry weight
phosphorous soil availability
enough, but is not all available to plants
phosphorous dry weight in plan
0.3-0.5% of plants dry weight
2 major stores of phosphorous in soil
organic and inorganic (a lot of which is unavailable)
-microorganisms needed to convert between the two
natural ecosystems and phosphorous availability over time
they progressively lose P and become increasingly P limited (10-100’s thousands of years) (retrogressive)
stages of an ecosystem
- progressive
- maximal biomass
- retrogressive
phosphorous fertiliser =
- using too much, going to run out.
- more going into ocean, not soil
- recycling our own waste, is v low
3M tonnes of P in human excrement how much ends back in land?
0.3 M tonnes
conventional sanitation systems lead to
linear flows of nutrients from agriculture, via humans to recipient water bodies
-need to find more of a cycle systems, not much is recycled back to agriculture
sustainable crop production depends on sustainable ___ supplies
nutrient supplies
human excrement is rich in ____
nutrients that have come from the soil, must try and put it back onto land
are there any substitutes for phosphorous?
NO (unlike fossil fuels, not alternatives)
(Elser and Bennett 2011) how much phosphorous left at current rates of use?
300 years, (but were using more and more due to increasing pop and increased demand for fertiliser) so probs less
do we know how much phosphate rock is left?
no, mining companies keeping it private
how can we save the phosphorous we have and feed more?
- change diet (veg)
- food chain efficiency
- agricultural efficiency
- food waste
loss of phosphorous
- landfill
- erosion (soil)
- into non-arable soil
- oceans (water ways)
P fertiliser: adding phosphorous to soil is great but what is one issue
phosphorous in soil isn’t necessary the problem, it binds in soil. must be available in soil
-those who needs it can’t afford it
use of “biosolids” as a form of fertiliser
- good results, work better than mineral fertiliser
- reduce extent of nutrient wash out of agricultural fields
micro plastics back into soils effects =
- unsure of effects
- earthworms are increased mortality and reduced growth rate with increasing amount of plastics
integrated life cycle management:
- waste is a resource, recycling is an option?
- animal manure adds to GHG and environmental pollutions
- could provide biogas and fertiliser through anaerobic digestion
- BUT what are the consequences for soil carbon? as it won’t be put back into soil
most P in soils is in..
insoluble chemicals unavailable to plants
- the conc of plant-available P is very low in most soils
- large stores of P occur in organic matter and non-exchangeable inorganic compounds
P is present as an __ in all soils
- -anion (-)
- participates in anion exchange and chemisorption and forms insoluble precipitates w Ca,Fe,Al
the conc of Ca, Si, Fe and Al are all many orders of magnitirues ___ than the conc of P
higher
P availability is controlled by
pH, and greatest in slightly acidic environments pH 6-7
soil solution of P and plants
all P must go through soil solution, but the amount of P in soil solution is TINY
problems of low P availability and mobility in soil: how do plants cope?
- main P is at top of soil (nitrogen disperses)
- diff plants have diff root dispersal
- increased SA & proliferation
- root hairs
- mycorrhizas
- specialised roots
- –proteoid root
role of microbes in phosphorous cycle (organic P)
if P < 0.2% they will take in P and use for themselves, if it is >0.2% they will release mineral phosphorous (phosphate) as they process it
temporal plant activity for P
- some take it up and store it
- internal recycling
- -for later in year
what can be found in volcanic rock and is released by__
- phosphorous, released slowly by weathering
- stones provide phosphorous for a time
- Basalt rock contain weather able apatite (Ca phosphate)
- used to rebuild and provide soil P
Taylor et al 2015 identify abundant reserves of basalt rock on the continents in excess of
14,000,000,000,000 (14 trill) tonnes
containing 35,000,000,000 (bill) of P2O5 (phosphorous)
–nearly another 1000 years of cropping using fertiliser as we do
risks of large-scale rock dust fertiliser use
- energy, GHG and economic costs of rock mining and grinding
- silicate dusts health risks
- potential irreversible on biogeochemistry, ecosystems ad soils
- publicly accepted?
phosphorous often limits __ in nature
plant growth
-especially on very ancient and deeply weathered soils
global food productions has become very dependent on
P fertilisers
-but the current source material (P-rich rocks) are a finite resource that is being rapidly depleted
alternatives to P-rich rock fertilisers
fast-weathering basalt which are much more abundant and may deliver co-benefits such as Si and trace elements, as well as generate clays
substantial losses of P fertiliser are occurring through ___
soil erosion and unidirectional flows through food supply system to human excrement
___ N:P ratios can indicate which of these elements is limiting plant growth
Foliar (leaf)
