Nitrogen

Question 1

Past farming

Answer 1

Recycling of nutrients or adding in through natural processes
Local conditions determined amount of produce
Societies developed complex systems to return nutrients to soil e.g. manure and compost
Intercropping and rotations to diversify what nutrients were extracted e.g. squash, beans and maize
Some practices to enhace weathering and nutrient release e.g. fire stick farming and increase productivity of edible plants

Question 2

Past limited urban areas

Answer 2

Spatial separation of homes, fields and soils
Limited size can result in overuse and famine
Local conditions can work against you
Soil degradation can result in fewer nutrients
Urban areas expanded too much so couldn’t cope
External inputs needed

Question 3

Timeline of growth

Answer 3

1800s - importance of N and P discovered, wars over reserves and reources
1900s - Haber Bosch process, make ammonia fertiliser
1940s - rock phosphate mining accelerates, P became more limiting so needed to match N
1960s - green revolution, plant breeding to better mine nutrients and increase productivity
Future - use of microbes

Question 4

Industrialised methods

Answer 4

Disconnection between ecosystem and crops
Using fertiliser to replace soil services - external inputs
Disruption of microbial cycle and less reliance of microbes so less beneficial
Less efficient and wasteful, too much added so leaching occurrs
Less famine w population expansion, better health
less land for same crop quantity
Limited P supply
Overapplication = toxicity

Question 5

N cycle

Answer 5

Fixation - atmosphere (N2) to soils (NH3)
Nitrification - within soil, ammonium to nitrite and nitrate (NH4 to NO2); make available for plants
Denitrification - soil (NO2) to atmosphere (N2O) via NO
DNRA - within soil, NO2 to NH4; w/ consuming biomass
Anammox - ammonia (NH3) into dinitrogen (N2)

Question 6

Microbes

Answer 6

Control processes
Diazatrophs - N fixation but lots of energy and low O2 needed; fix N for themselves
Denitrifiers - produce energy through respiration; affected by O2, waterlogging, carbon etc.; rate increases as fertiliser added

Question 7

Microbial ecology to reduce dependence on fertiliser

Answer 7

Reduce N loss - promote conditions to favour N retention; use of leys and crops and non crops
Enhance N fixation - use of legumes and use bacteria to fix N; reduce competition
Symbioses - engineer into other crops to make nodules; crops to produce their own N w/ bacteria but hard for eukaryotes, engineer into mitochondria or chloroplasts