This document discusses nitrogen cycling in agriculture and opportunities to improve nitrogen use efficiency (NUE). It notes that improving NUE is important to reduce costs, fossil fuel use, and nitrogen losses to the air and water. The core of the nitrogen cycle is complicated, and there is no quick way to predict nitrogen release from soils. Improving NUE requires no quick fixes and involves assessing risk and eliminating 'leaky' practices that cause nitrogen to leach. The document recommends using tools like the RB209 Fertiliser Manual and Tried & Tested SNS calculator to help estimate crop needs and soil nitrogen supply to guide fertilizer application rates and improve NUE.

1. Nitrogen cycling:
risks and opportunities
Keith Goulding
Head: Department for Sustainable
Soils and Grassland Systems
Rothamsted Research

2. 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.

3. Example: problem of poor NUE of meat
production. Intensive pig production from field to
fork
‘Reactive nitrogen in the environment.’ UNEP 2007

4. 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
dairy
pig/arable
organic
dairy (clover)

5. At the core, the complicated nitrogen cycle

6. Organic
Matter
Microbial
Biomass
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 predicting
N release from soils

7. Worst case scenario for SMN?
kg ha-1

8. 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
SoilWaterNitrate(ppm)
0
5
Temperature(°C)
Low N Plot
High N Plot
N release very variable through the season:
nitrate in soil on Broadbalk field, Rothamsted
Tony Miller, Rothamsted

9. Improving NUE
 No quick fixes

10. 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.

11. Probably not like this!
Better manure management

12. 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

13. ‘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

14. Improving NUE involves assessing risk and
eliminating ‘leaky’ practices
N leached
(kg ha-1
)

15. Could also consider:
 Min Till
 Precision seeding and fertiliser
application
 Fertigation

16. 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.