Lecture 9: Nitrogen cycling, fertiliser and pollution Flashcards
mineral nutrient most in demand by plants
nitrogen
4th most abundant element in plants
nitrogen, after C,H and O
nitrogen content in rocks and minerals
exceedingly low
what element most often limits plant growth in nature
nitrogen
what element is the main constituent of artificial fertilisers
nitrogen
nitrogen in rocks?
we thought a little amount, but Houlton et al 2018 has shown there is nitrogen in earth surface rocks
nitrogen dry weight in shoots
1-5 %
what is nitrogen in plants needed for
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)
nitrogen and photosynthesis relationship
more nitrogen –> more photosynthesis in general across spread of species
where is the most nitrogen? land/atmosphere
atmosphere
most nitrogen organic/inorganic?
organic
most organic nitrogen dead/alive?
dead organic matter
of the alive organic nitrogen where is the majority of it found?
94% in plants
nitrogens state:
exists in orange of oxidation states, different ionic forms and physical states
most of nitrogen transfers in the cycle are caused by
microorganisms
main pool of nitrogen in the ground
soil = organic N
soil profile-distribution in soil
higher conc at surface but disperses down into earth
do roots respond to localised nitrogen supplies
yes increasing SA
-increased branching
humans effect on the biogeochemical N cycle
altered more than the carbon cycle
through..fertiliser factories, legume cropping
use of N fertilisers?
still growing, as growing pop
-do we need to use this much?
safe level of N fertilisers =
amount we were using back in 1970’s, but then we had much smaller pop. Is this realistic?
commercial fertiliser is responsible for _____& of the worlds food production
40-60%
fertiliser worldwide distribution
some parts (africa) noticing enough -others (developed countries) using too much
global food proaction is currently strongly depended on
nitrogen fertiliser inputs
ideal Nitrogen fertiliser conc w yields
we should reduce N fertiliser a little, to achieve relatively good yields, less waste (graph)
globally ___ of N fertiliser is not used by crops
more than 50%
legume benefits to N concentrations
nitrogen fixing legumes put organic nitrogen back into soil
-use in rotation?
Ammonium source + sinks (NH4+)
Sources:
- ammonification (organic materials –> mineral nitrogen)
- clay weathering
- diffusion/mass flow
Sinks
- plant uptake
- clay fixations
- nitrification
- diff/mass flow
in acid soils nitrification is
inhibited (pH<4.5)
NH4+ is a cation/anion and is taken up with release of __
CATION
release of H+ (plants release as they take up NH4+)
when NH4+ is the main N source, further soil acidification follows
a positive feedback
–releasing of H+
what do nitrifying bacteria do
nitrifying bacteria NH4+ –> NO3-
- result in 4H+ and nitric acid
- –soils become acidified
denitirifcation =
removal of oxygen
-process in poorly aerated soils
which is more temperature sensitive nitrification/ ammonification
Nitrification
-slows down at high temps
ammoniification =
organic nitrogen –> ammonia by bacteria
N2O =
major GHG
- major source is soils, from fertilisation (rice productivity)
- worse than CO2 (nearly 300X)
- atmosphere increase, 89% due to emissions of cultivated soils
UK fertiliser use has
peaked
- become more caring with use
- cost
- precision agriculture (sensors in tractors to detect how much fertiliser needed)
- pollution
legumes in cropping systems
-they reduce nitrous oxide emissions
-reduce N fertiliser requirements
-reduce nitrate leaching
HOWEVER;
grain legumes reduce gross margins in 3/5 regions
—reduced yields?
cereals that fix nitrogen????
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
ammonia emissions in UK
livestock are major contributors (cattle, poultry)
slurry spreading efficiency =
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
nitrogen cycling depends upon a complex series of _____ transformations of atmospheric __ and recycling of organic __
microbial
N2
organic N
nitrogen cycling is highly dependent on environmental controls:
temperature, water, oxygen
adaptions to conserve N in ecosystems can result in strong accumulation of ____ in humus
soil carbon
