Lecture 3

Question 1

monocultures vs mixtures of plants co-existing

Answer 1

• monoculture = intensive agriculture

- monoculture are rare in nature

Question 2

patio-temporal effects of monoculture cropping

Answer 2

• huge areas growing the same limited number or crops/varieties makes them vulnerable to pests, diseases and extremes of weather and to nutrient losses
• more diverse spread the risks

Question 3

main arable crops in the UK

Answer 3

wheat, barley and oilseed

Question 4

EU Common Agricultural Policy 3-crop rule

Answer 4

this rule requires UK farms of mor ethan 30 hectares have to plant at least 3 crops, with 2 of the main crops not exceeding 95% of the arable area

Question 5

growing the same crop more frequently in rotations builds up

Answer 5

pathogens and reduces yields

-seen in oilseed rape

Question 6

why do we grow so much oilseed rape?

Answer 6

• good soil conditioner for wheat
• grown before wheat = wheat yields are better
• common in heavy land
• • but too much of this rotation (W,W,R) leads to issues (black grass and oilseed rape pest & disease control)

Question 7

‘heavy’ land =

Answer 7

clay-rich

Question 8

rotating crops: more diverse rotations

Answer 8

less profit

-but better for disease/ environment

Question 9

crop production depends on

Answer 9

nutrient supplies

• soil provides an important store, but when fertilisers added soil must have good capacity to hold onto nutrients so its not washed away
• rate of nutrient loss from soil erosion and leaching usually exceeds natural replenishment of nutrients

Question 10

component for holding onto nutrients in soil

Answer 10

Clays

-they generate parallel sheets

Question 11

Clays layers:

Answer 11

Highest surface area 
-Smectite
- vermiculite (both swelling clays) 
-illite/ mica 
-kaolinite 
smallest SA

Question 12

smectite and vermiculite =

Answer 12

-can hold ions between
-huge SA (12.5g = 1 ha area)
Swelling clays (swell & shrink)

Question 13

building blocks of clays =

Answer 13

• silicon tetrahedra
• aluminium / magnesium octahedra
• -often alteration between the 2 layers

Question 14

colloidal =

Answer 14

clay material

Question 15

clay materials have a lot of + / - charge

Answer 15

negative

-part is permanent / down to pH

Question 16

Humus is an

Answer 16

• organic matter
• high pH dependent charge
• reasonable permeant charge
• able to move ions in soil
• hold nutrients
• when washed out, can be replaced (new ion storage capacity) for nutrients

Question 17

movements of ion with clay

Answer 17

-Clay is - charge, so positive ions in solution attracted to surface (they don’t bond but are held)

Question 18

movements of ion with clay if new ions added (fertiliser)

Answer 18

new ions go into bulk solution, they will move in and displace other + ions near clay - surface

Question 19

___ & clays play a vital role in holding nutrient reserves in soil

Answer 19

organic matter

• especially in winter
• but these are easily eroded
• and organic matter can be lost by oxidation through tillage and other practices

Question 20

pathways of nutrients into crop

Answer 20

in =
diffusion and mass flow

out = leaking and extrusion

Question 21

how do plants facilitate the uptake of nutrients

Answer 21

• H+ ATPase (pump)

- displace protons for cations

Question 22

colloids:

Answer 22

• v small charged particles or macromolecules
• some have permanent, some pH ,some BOTH
• attract ions of opposite charge

Question 23

roots and cell walls of microorganisms normally have a net ___ charge

Answer 23

negative

–attract cations

Question 24

CATION/ANION exchange

Answer 24

• quick
• reversible
• driven by conc of reactant and products

Question 25

e.g. of niche separation

do plants compete w each other for nutrients, or do plants obtain resources form different niches

Answer 25

• soil pore size/root dimension
• separation of roots
• different root phonologies
• different nutrient source preferences (ammonium vs Nitrate)
• ability to use nutrients that are unavailable to other plants
• extensive vs intensive root systems

Question 26

niche separation: different root phenologies e.g.

Answer 26

bluebells

• root growth in sept-Nov
• peak in march
• root growth = when trees r losing leaves, less competition

Question 27

niche separation: ability to use nutrients that are unavailable to other plants

Answer 27

• symbiotic N fixation
• use of a-a N and organic N
• use of organic P
• mobilisation of insoluble molecules

Question 28

niche separation: extensive vs intensive root systems

Answer 28

ability to respond to patchy distribution of nutrients

• some show targeting of root systems into nutrient rich patches
• specialised roots
• proteoid roots

Question 29

have we ended up breeding crops with poor root systems?

Answer 29

• if we expanded arable land into grazing land, could we use perennial plants (larger root systems) perennial Wheat grass vs wheat

Question 30

light capture by crops

Answer 30

• solar energy light captured by crop, may & june = high, drops off quickly after this
• still light produced june-august but due to plant being matured = less carbon fixation
• perennial crops would utilise this better

Question 31

increasing plant diversity increases ____

Answer 31

productivity

• but in arable farming –> harvest? options?
• • crop rotations
• • green manures
• • agri-forestry
• • companion cropping

Question 32

clover & wheat sown together then barley in second year

Answer 32

• addition of clover = really high barely productivity (no fertiliser)
• but reduced wheat productivity – need N fertiliser

Question 33

beans and oil seed crop at same time

Answer 33

-beans on their own out perform the mixture

Question 34

niche separation: separation of roots

Answer 34

(to cope with water-limitation- desert) Some high, some low, dry areas= root high, wet = deeper)
- crops v small amount of roots <2kgm^3 compared to grassland