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SS > soil macronutrients (N, P, K) > Flashcards

soil macronutrients (N, P, K) Flashcards

1
Q

what are 4 inputs of P for soils

A
  1. weathering of rocks (phosphate)
  2. litter and necromass SOM
  3. fertilisers
  4. atmospheric deposition (dust)
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2
Q

what form of P do plants need

A

inorganic phosphate

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3
Q

Describe how P is mineralised

A

through the decomposition of SOM microbes mineralise into phosphate (PO4 -3_

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4
Q

decribe the process of P immobilisation

A

microbes compete with plants for phosphate in soils.

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5
Q

are there organic forms of P in soil

A

yes, organic P is dissolved in water and can be taken up by microbes and not plants

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6
Q

what is adsorption if P and when does it occur

A

a form of P fixation it is an abotic process, it occurs in low pH (acidic soils) where Fe/Al surfaces can adsorb P.

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7
Q

what are the 2 main losses of P

A
  1. through leaching and runoff with high rainfall (low dissolved P)
  2. through erosion loss of particles (high P in solid fraction)
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8
Q

do old or young soils have more P? eg think of AUS

A

P is mainly in primary minerals therefore P is higher in young soils and in weathered old soils ie australia, P is low because of lack of primary minerals.

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9
Q

what phosphate ions occur in the soil and how do thier concentrations differ with pH

A

HPO4 2-
H2PO4-
PO3 4- (only in high pH)

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10
Q

why is P have low concentrations in solution?

A

mobility is low because it reacts with soil particles .

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11
Q

what are 6 plant strategies to increase P uptake?

A
  1. symbiotic: root hairs and mycorrhizal fungi (AMF) hyphae
  2. increase root surface area with root hairs
  3. organic acids released in acidic soils to chelate with Fe or Al
  4. organic acids to dissolve Ca in alkaline soils
  5. phosphatase enzymes to increase P decomposition
  6. enhance growth of microbes that uptake soluable P
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12
Q

what is precipiation and how does it occur (P)

A

a form of P fixation

an abotic process in high pH soils (akaline) where Ca minerals precipitate with P

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13
Q

Australian plant adaptation to low P

A

form cluster roots (dense structures) that solubilise P

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14
Q

what are the 2 forms of P fixation

A
  1. low pH (fe, al and mn) adsoptio this decreaes availaibility
  2. high pH (ca, mg) precipitation to form ca/mg phosphates this decreases solubility
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15
Q

best pH for P availability

A

6-7 (neutral)

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16
Q

what does the P fertilisers debate disuss?

A

most fertilisers derived form rock (mainly in morocco)

dissagreement on amount of stock left. p mining increasing exponentiuall and need other alternatives maybe waste?

17
Q

what form of K is in soils

A

there is only one form K+ cation. there is no gas phase and not involved in OM can be exchanged with other cations on clay or OM complex

18
Q

3 inputs of K into soils

A
  1. mainly through weathering of primary minerals feldspar and mica and secondary clays
  2. rainfall washing K from leaves into soil
  3. fertilisers
19
Q

3 loss of K

A
  1. harvest
  2. erosion
  3. runoff
    biggest is harvest, low for erosion and runoff
20
Q

what is the purpose of K in soils

A

K is a macronurtient for plants essential to activating enzymes for photosythesis, metabolism. it does not get incorporated into plant structures

21
Q

how can K increase tolerance

A

drought tolerance: ion regulates osmotic water potential

pest tolerane study

22
Q

sign of K deficiency

A

high mobility plants locate K to young leaves when stressed therefore symptoms in oldest leaves (K needed for plant functions)

23
Q

what is luxury consumption?

A

when plants uptake more K than needed and does not add to their plant growth however can help with future stresses

24
Q

why are K fertilisers necessary

A

plants uptake lots of K and K is removed once harvested. K fertilisers are easy to make and ulimited.
inputs (weathering and deposition) are slow processes therefore K fertilsier is needed to replace.

25
Q

where is the biggest stock of N

A

atmosphere in form of n2 gas ~80% of air is N.

26
Q

how does N enter the soil

A

N is not added through weathering but through biological fixation and deposition.

  1. fixation: microbes fix N2
  2. deposition through rainwater
27
Q

describe ammonification

A

N in SOM is decomposed by microbes and mineralised into NH4 + (ammonia)

28
Q

describe nitrification, what conditions are needed, and what can it cause

A

occurs under aerboic conditions
as O is needed for process.
ammonium mineralised into nitrite(NO2- ) (quickly) into nitrate (NO3 -). therefore more nitrate in soils and nitrite can be toxic in high Concentrations
causes acificication (H+) needed buffering

29
Q

what is the available nitrogen pool

A

plants can only uptake mineralised forms eg ammonium and nitrate

30
Q

how is N immobilized (2 ways = abiotic and biotic

A

nitrogen taken up microbes anfd compete with plants unavailable to pltants when locked by SOM

abotic process of immbolising ammonium fixed within caviities of clay structure between 2 layers

31
Q

4 ways N is lost

A
  1. leaching, nitrate anion is mobile and can leach
  2. volatilisation, ammonia gas in soils with high pH
  3. anammox and nitrification, (process where ammonia oxidised by nitrite instead of O to form N2 gas. ammonium and nitrite transformed into gas
  4. denitrification nitrate turned into gas (O removed) with under anaerobic conditions. higher than 75% moisture all N2 produced no N is fixed
32
Q

what microbe relationships fix N

A

symbiosis with plants eg legumes and non legumes (angiosperms), some are assciative symbotic and some non symbotic

33
Q

how does N get fixed process

A

strong triple bond between N2 gas requires a lot of energy, microbes get this with symbiosis carbon from plant. most is through symbiotic relationship

34
Q

how does high N availability effect N fixation

A

N fixation decreases with available N in soils.

35
Q

human sources of N in atmoshere

A

through human acivity, agriculture (ammonia fertiliser and NH3 from livestock gas.
fossil fuels also release NO and NO2

36
Q

how can N losses be controlled

A
  1. slow release fertiliser
  2. urease inhibitors to slow hydroloiss and prevent ammonia volatilisation in high PH soils
  3. Nitrifiacation inhibitors, inhibit acivity of some microbes to slow process of nitrification and prevent nitrate leaching by keeping as ammonium
37
Q

what is eutrophication

A

high level of N into surface water cuases alagal blooms which deplete O when die.

38
Q

what is volatilisation

A

forming ammonia from ammonium in basic soils (high pH)

SS (10 decks)

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