Lecture 3 Flashcards
monocultures vs mixtures of plants co-existing
- monoculture = intensive agriculture
- monoculture are rare in nature
patio-temporal effects of monoculture cropping
- 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
main arable crops in the UK
wheat, barley and oilseed
EU Common Agricultural Policy 3-crop rule
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
growing the same crop more frequently in rotations builds up
pathogens and reduces yields
-seen in oilseed rape
why do we grow so much oilseed rape?
- 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)
‘heavy’ land =
clay-rich
rotating crops: more diverse rotations
less profit
-but better for disease/ environment
crop production depends on
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
component for holding onto nutrients in soil
Clays
-they generate parallel sheets
Clays layers:
Highest surface area -Smectite - vermiculite (both swelling clays) -illite/ mica -kaolinite smallest SA
smectite and vermiculite =
-can hold ions between
-huge SA (12.5g = 1 ha area)
Swelling clays (swell & shrink)
building blocks of clays =
- silicon tetrahedra
- aluminium / magnesium octahedra
- -often alteration between the 2 layers
colloidal =
clay material
clay materials have a lot of + / - charge
negative
-part is permanent / down to pH
Humus is an
- 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
movements of ion with clay
-Clay is - charge, so positive ions in solution attracted to surface (they don’t bond but are held)
movements of ion with clay if new ions added (fertiliser)
new ions go into bulk solution, they will move in and displace other + ions near clay - surface
___ & clays play a vital role in holding nutrient reserves in soil
organic matter
- especially in winter
- but these are easily eroded
- and organic matter can be lost by oxidation through tillage and other practices
pathways of nutrients into crop
in =
diffusion and mass flow
out = leaking and extrusion
how do plants facilitate the uptake of nutrients
- H+ ATPase (pump)
- displace protons for cations
colloids:
- v small charged particles or macromolecules
- some have permanent, some pH ,some BOTH
- attract ions of opposite charge
roots and cell walls of microorganisms normally have a net ___ charge
negative
–attract cations
CATION/ANION exchange
- quick
- reversible
- driven by conc of reactant and products
e.g. of niche separation
do plants compete w each other for nutrients, or do plants obtain resources form different niches
- 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
niche separation: different root phenologies e.g.
bluebells
- root growth in sept-Nov
- peak in march
- root growth = when trees r losing leaves, less competition
niche separation: ability to use nutrients that are unavailable to other plants
- symbiotic N fixation
- use of a-a N and organic N
- use of organic P
- mobilisation of insoluble molecules
niche separation: extensive vs intensive root systems
ability to respond to patchy distribution of nutrients
- some show targeting of root systems into nutrient rich patches
- specialised roots
- proteoid roots
have we ended up breeding crops with poor root systems?
- if we expanded arable land into grazing land, could we use perennial plants (larger root systems) perennial Wheat grass vs wheat
light capture by crops
- 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
increasing plant diversity increases ____
productivity
- but in arable farming –> harvest? options?
- crop rotations
- green manures
- agri-forestry
- companion cropping
clover & wheat sown together then barley in second year
- addition of clover = really high barely productivity (no fertiliser)
- but reduced wheat productivity – need N fertiliser
beans and oil seed crop at same time
-beans on their own out perform the mixture
niche separation: separation of roots
(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
