Lecture 6: Aeration and nutrient cycling

Question 1

Healthy soil aeration

Answer 1

solids with bound water with large pores

Question 2

poor draining clays

Answer 2

decreasing aeration with soil depth and season

Question 3

aggregate size

Answer 3

large causes anaerobic soil centre

Question 4

nitrogen cycle

Answer 4

sedimentary OM provides organic N
mineral weathering provides NH4 and NO3
organic N neutralised to NH4
nitrification NH4 to NO2
denitrification NO3 to N2O or N2
fixation

Question 5

nitrification (NH4+ to NO2-)

Answer 5

NH4+ to NO2-
aerobic
archaea
nitrosomes
nitrosococcus

Question 6

nitrification (NO2- to NO3-)

Answer 6

nitrobacter and nitrospira
release CO2 for C for growth

Question 7

denitrification (NO3- to N2O and N2)

Answer 7

pracoccus denitrificans and pseudomonas
need anaerobic and root exudates
anoxic needed

Question 8

podzolisation

Answer 8

soil forming processes where dissolved OM moved with water deeper into soil

Question 9

podzol

Answer 9

under-ashed soil

Question 10

podzol horizons

Answer 10

organic surface layer (O)
topsoil (A)
eluviated horizon (E) - no OM
illuviated horizon (B) - redposition of OM
parent material (R)

Question 11

surface soil layer pod

Answer 11

acidic as decomposers inhibited

Question 12

iron pans

Answer 12

low pH at top and higher at bottom
rust forms

Question 13

nutrient cycling

Answer 13

biomass store
inorganic store
organic store
nutrient entering
nutrient escaping

Question 14

absorption

Answer 14

inorganic to biomass nutrients

Question 15

mineralisation

Answer 15

organic to inorganic

Question 16

immmobilisation

Answer 16

organic to biomass

Question 17

nitrogen cycle fixation

Answer 17

legumes, lightning, bacteria (rhizobia)

Question 18

rhizobia

Answer 18

fix N in return for C

Question 19

legumes

Answer 19

signal to rhizobia via alkaloids
positive chemotaxis
Nod-factors induced to form nodules

Question 20

root nodule formation

Answer 20

nod factor detected
flaccid to curled
open up tip
infection thread
colonise
differentiation of cells
vascular system produced
gas tight so no oxygen

Question 21

leghaemoglobin

Answer 21

anaerobic conditions around rhizobia
buffers oxygen for optimal N fixation

Question 22

phosphorous cycle

Answer 22

weathering of bedrock
unavailble organic converted to inorganic via mineralisation

Question 23

phosphate forms

Answer 23

dissolved most available
labile phosphomonomers require hydrolysis but low energy needed
phosphodiesters harder to break
inositol phosphate hard to break down

Question 24

what is undisputed about P crisis

Answer 24

high grade rock depleted
harder to access
lower P conc.
impurities
waste
extraction
prices
environmental cost

Question 25

disputed P crisis

Answer 25

size of reserves
longeivity of supply
future demand

Question 26

dealing with P crisis

Answer 26

engineer sustainable organic phytate fertilisers