Lecture 8

Question 1

is phosphorous finite?

Answer 1

yes

Question 2

phosphorous required for in plants ( Small pic)

Answer 2

• phospholipid cell membrane
• ATP/ADP
• essential element for life

Question 3

2 nutrients which limit plants growth

Answer 3

N & P

Question 4

nitrogen dry weight in plant

Answer 4

1-5% of plant dry weight

Question 5

phosphorous soil availability

Answer 5

enough, but is not all available to plants

Question 6

phosphorous dry weight in plan

Answer 6

0.3-0.5% of plants dry weight

Question 7

2 major stores of phosphorous in soil

Answer 7

organic and inorganic (a lot of which is unavailable)

-microorganisms needed to convert between the two

Question 8

natural ecosystems and phosphorous availability over time

Answer 8

they progressively lose P and become increasingly P limited (10-100’s thousands of years) (retrogressive)

Question 9

stages of an ecosystem

Answer 9

• progressive
• maximal biomass
• retrogressive

Question 10

phosphorous fertiliser =

Answer 10

• using too much, going to run out.
• more going into ocean, not soil
• recycling our own waste, is v low

Question 11

3M tonnes of P in human excrement how much ends back in land?

Answer 11

0.3 M tonnes

Question 12

conventional sanitation systems lead to

Answer 12

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

Question 13

sustainable crop production depends on sustainable ___ supplies

Answer 13

nutrient supplies

Question 14

human excrement is rich in ____

Answer 14

nutrients that have come from the soil, must try and put it back onto land

Question 15

are there any substitutes for phosphorous?

Answer 15

NO (unlike fossil fuels, not alternatives)

Question 16

(Elser and Bennett 2011) how much phosphorous left at current rates of use?

Answer 16

300 years, (but were using more and more due to increasing pop and increased demand for fertiliser) so probs less

Question 17

do we know how much phosphate rock is left?

Answer 17

no, mining companies keeping it private

Question 18

how can we save the phosphorous we have and feed more?

Answer 18

• change diet (veg)
• food chain efficiency
• agricultural efficiency
• food waste

Question 19

loss of phosphorous

Answer 19

• landfill
• erosion (soil)
• into non-arable soil
• oceans (water ways)

Question 20

P fertiliser: adding phosphorous to soil is great but what is one issue

Answer 20

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

Question 21

use of “biosolids” as a form of fertiliser

Answer 21

• good results, work better than mineral fertiliser

- reduce extent of nutrient wash out of agricultural fields

Question 22

micro plastics back into soils effects =

Answer 22

• unsure of effects

- earthworms are increased mortality and reduced growth rate with increasing amount of plastics

Question 23

integrated life cycle management:

Answer 23

• 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

Question 24

most P in soils is in..

Answer 24

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

Question 25

P is present as an __ in all soils

Answer 25

• -anion (-)

- participates in anion exchange and chemisorption and forms insoluble precipitates w Ca,Fe,Al

Question 26

the conc of Ca, Si, Fe and Al are all many orders of magnitirues ___ than the conc of P

Answer 26

higher

Question 27

P availability is controlled by

Answer 27

pH, and greatest in slightly acidic environments pH 6-7

Question 28

soil solution of P and plants

Answer 28

all P must go through soil solution, but the amount of P in soil solution is TINY

Question 29

problems of low P availability and mobility in soil: how do plants cope?

Answer 29

• 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

Question 30

role of microbes in phosphorous cycle (organic P)

Answer 30

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

Question 31

temporal plant activity for P

Answer 31

• some take it up and store it
• internal recycling
• -for later in year

Question 32

what can be found in volcanic rock and is released by__

Answer 32

• 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

Question 33

Taylor et al 2015 identify abundant reserves of basalt rock on the continents in excess of

Answer 33

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

Question 34

risks of large-scale rock dust fertiliser use

Answer 34

• energy, GHG and economic costs of rock mining and grinding
• silicate dusts health risks
• potential irreversible on biogeochemistry, ecosystems ad soils
• publicly accepted?

Question 35

phosphorous often limits __ in nature

Answer 35

plant growth

-especially on very ancient and deeply weathered soils

Question 36

global food productions has become very dependent on

Answer 36

P fertilisers

-but the current source material (P-rich rocks) are a finite resource that is being rapidly depleted

Question 37

alternatives to P-rich rock fertilisers

Answer 37

fast-weathering basalt which are much more abundant and may deliver co-benefits such as Si and trace elements, as well as generate clays

Question 38

substantial losses of P fertiliser are occurring through ___

Answer 38

soil erosion and unidirectional flows through food supply system to human excrement

Question 39

___ N:P ratios can indicate which of these elements is limiting plant growth

Answer 39

Foliar (leaf)