Lecture 9: Nitrogen cycling, fertiliser and pollution

Question 1

mineral nutrient most in demand by plants

Answer 1

nitrogen

Question 2

4th most abundant element in plants

Answer 2

nitrogen, after C,H and O

Question 3

nitrogen content in rocks and minerals

Answer 3

exceedingly low

Question 4

what element most often limits plant growth in nature

Answer 4

nitrogen

Question 5

what element is the main constituent of artificial fertilisers

Answer 5

nitrogen

Question 6

nitrogen in rocks?

Answer 6

we thought a little amount, but Houlton et al 2018 has shown there is nitrogen in earth surface rocks

Question 7

nitrogen dry weight in shoots

Answer 7

1-5 %

Question 8

what is nitrogen in plants needed for

Answer 8

as a constituent of proteins, aa, nucleic acids, some membrane lipids
–> largest requirement = Ribulose Bisphosphate Carboxylase (most abundant enzyme in the world, allows plants to fix CO2)

Question 9

nitrogen and photosynthesis relationship

Answer 9

more nitrogen –> more photosynthesis in general across spread of species

Question 10

where is the most nitrogen? land/atmosphere

Answer 10

atmosphere

Question 11

most nitrogen organic/inorganic?

Answer 11

organic

Question 12

most organic nitrogen dead/alive?

Answer 12

dead organic matter

Question 13

of the alive organic nitrogen where is the majority of it found?

Answer 13

94% in plants

Question 14

nitrogens state:

Answer 14

exists in orange of oxidation states, different ionic forms and physical states

Question 15

most of nitrogen transfers in the cycle are caused by

Answer 15

microorganisms

Question 16

main pool of nitrogen in the ground

Answer 16

soil = organic N

Question 17

soil profile-distribution in soil

Answer 17

higher conc at surface but disperses down into earth

Question 18

do roots respond to localised nitrogen supplies

Answer 18

yes increasing SA

-increased branching

Question 19

humans effect on the biogeochemical N cycle

Answer 19

altered more than the carbon cycle

through..fertiliser factories, legume cropping

Question 20

use of N fertilisers?

Answer 20

still growing, as growing pop

-do we need to use this much?

Question 21

safe level of N fertilisers =

Answer 21

amount we were using back in 1970’s, but then we had much smaller pop. Is this realistic?

Question 22

commercial fertiliser is responsible for _____& of the worlds food production

Answer 22

40-60%

Question 23

fertiliser worldwide distribution

Answer 23

some parts (africa) noticing enough 
-others (developed countries) using too much

Question 24

global food proaction is currently strongly depended on

Answer 24

nitrogen fertiliser inputs

Question 25

ideal Nitrogen fertiliser conc w yields

Answer 25

we should reduce N fertiliser a little, to achieve relatively good yields, less waste (graph)

Question 26

globally ___ of N fertiliser is not used by crops

Answer 26

more than 50%

Question 27

legume benefits to N concentrations

Answer 27

nitrogen fixing legumes put organic nitrogen back into soil

-use in rotation?

Question 28

Ammonium source + sinks (NH4+)

Answer 28

Sources:

• ammonification (organic materials –> mineral nitrogen)
• clay weathering
• diffusion/mass flow

Sinks

• plant uptake
• clay fixations
• nitrification
• diff/mass flow

Question 29

in acid soils nitrification is

Answer 29

inhibited (pH<4.5)

Question 30

NH4+ is a cation/anion and is taken up with release of __

Answer 30

CATION

release of H+ (plants release as they take up NH4+)

Question 31

when NH4+ is the main N source, further soil acidification follows

Answer 31

a positive feedback

–releasing of H+

Question 32

what do nitrifying bacteria do

Answer 32

nitrifying bacteria NH4+ –> NO3-

• result in 4H+ and nitric acid
• –soils become acidified

Question 33

denitirifcation =

Answer 33

removal of oxygen

-process in poorly aerated soils

Question 34

which is more temperature sensitive nitrification/ ammonification

Answer 34

Nitrification

-slows down at high temps

Question 35

ammoniification =

Answer 35

organic nitrogen –> ammonia by bacteria

Question 36

N2O =

Answer 36

major GHG

• major source is soils, from fertilisation (rice productivity)
• worse than CO2 (nearly 300X)
• atmosphere increase, 89% due to emissions of cultivated soils

Question 37

UK fertiliser use has

Answer 37

peaked

• become more caring with use
• • cost
• • precision agriculture (sensors in tractors to detect how much fertiliser needed)
• • pollution

Question 38

legumes in cropping systems

Answer 38

-they reduce nitrous oxide emissions
-reduce N fertiliser requirements
-reduce nitrate leaching
HOWEVER;
grain legumes reduce gross margins in 3/5 regions
—reduced yields?

Question 39

cereals that fix nitrogen????

Answer 39

No way, one fundamental reason. cereal = monocot,
different to dicot’s roots that form symbiotic bacteria
-nature hasn’t done it, its not going to

Question 40

ammonia emissions in UK

Answer 40

livestock are major contributors (cattle, poultry)

Question 41

slurry spreading efficiency =

Answer 41

spraying it you lose a lot of nitrogen

• ammonia lose up to 80%
• slurry injector (umbilical is best so tanker doesnt compress land) so goes straight into land

Question 42

nitrogen cycling depends upon a complex series of _____ transformations of atmospheric __ and recycling of organic __

Answer 42

microbial
N2
organic N

Question 43

nitrogen cycling is highly dependent on environmental controls:

Answer 43

temperature, water, oxygen

Question 44

adaptions to conserve N in ecosystems can result in strong accumulation of ____ in humus

Answer 44

soil carbon