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.