Nitrogen cycling:risks and opportunities
Keith Goulding
Head: Department for SustainableSoils and Grassland Systems
Rothamsted Research
Driving forces for better N utilisation
Projected population increase requires 50% more food by 2030; 70% more by 2050.
Royal Society says we need ‘Sustainable Intensification’. Cultivating more land risks destruction of forests and large carbon losses.
N is the key to yield in most countries, but making N fertiliser uses fossil fuels and produces greenhouse gases.
Must improve NUE to reduce costs, fossil fuel use and losses to air and water.
NB some room for greater use of legumes but not wholesale switch.
Example: problem of poor NUE of meat production. Intensive pig production from field to
fork
‘Reactive nitrogen in the environment.’ UNEP 2007
Example: N surpluses on some UK farms
N surplus (= N inputs – N in product; kg N/ha)
Fertiliser N input (kg N/ha)
sheep
arable
dairypig/arable
organic
dairy (clover)
At the core, the complicated nitrogen cycle
OrganicMatter
MicrobialBiomass
NH4+ NO3
-
Immobilisation
NitrificationAmmonification
Death &
decomposition
Mineral N
Organic Matter Mineral N
Approximate N content (kg ha-1) : 2000-20000 10-500
Mineralisation
Importance of N in soil organic matter
But still no quick and easy way of predictingN release from soils
Worst case scenario for SMN?
kg ha-1
0
100
200
300
400
500
600
21/10/03 10/11/03 30/11/03 20/12/03 09/01/04 29/01/04 18/02/04 09/03/04 29/03/04 18/04/04
So
il W
ater
Nitr
ate
(pp
m)
0
5
Tem
per
atu
re (°
C)
Low N Plot
High N Plot
N release very variable through the season:nitrate in soil on Broadbalk field, Rothamsted
Tony Miller, Rothamsted
Improving NUE
No quick fixes
RB209: The Basis of Good Practice Reliable information: soil type; regular soil analysis; cropping
fertiliser and manure history; nutrient balances; winter rainfall. Realistic estimate of crop yields and fertiliser needs; take account
of fertiliser prices. Estimate SNS: RB209; PLANET, ‘Tried and Tested’ Utilise available nutrients in organic manures. Careful selection of fertilisers – price and quality. Correct rate, method and timing of fertiliser
and manure applications; accuracy. Good record keeping.
Probably not like this!
Better manure management
Better manure management
Estimate or measure N content (RB209; MANNER); make allowance when calculating fertiliser applications
Recycle effectively – band spreading; injection
Where possible, apply from late winter onwards
Measure application rate Manure Management Plan
‘Tried & Tested’ SNS calculator
You can use our SNS calculator to help you determine the Soil Nitrogen Supply of your soil. You will need this index number when using the ‘Fertiliser Manual (RB209)’ for guidance on fertiliser application rates.
Tried & Tested SNS Calculator
Improving NUE involves assessing risk andeliminating ‘leaky’ practices
N leached(kg ha-1)
Could also consider:
Min Till
Precision seeding and fertiliser application
Fertigation
Acknowledgements
Rothamsted Research is an institute of the UK Biotechnology and Biological Sciences Research Council.
The UK Department for Environment, Food and Rural Affairs funded some of the research described in this talk.