Event Date

Can legumes solve the nitrogen problem?

Bob ReesSRUC

Science, innovation, and the empowerment of legumes, May 4th 2021

22 2Fowler et al, 2015. Atmospheric Chemistry and Physics. 15, p. 13849 - 13893

Global nitrogen cycle

Agriculture 60

Ocean 120

Natural 128BNF 308

Lightning 5

Combustion 40

Haber-Bosch 120

Tg N y-1

33 3

Halving nitrogen waste contributes to all of the UN’s Sustainable Development Goals

44 4

Summary of N flows in Europe

Humannutrit.

agricult soils

Livestock farming

Atmospheric N2 pool

Crop production

Atmdepos

17.6

7.1

11.8

1.5

2.14.5

2.3

1.0

3.1

Net import of food & feed

2Crop N2fix

Fertilizers

11.23.8

NH3,NOx& N2O

emission

Denitrifi-cation

N2 fixindust

& traffic3.4

Europe (EU27), around 2000. N fluxes in TgN/yr

Export by rivers to the sea

Net atmosph. export

9.32.4

3.5

6.84

6

13.8

0.4

4.75.8

3.7

0.83.2

0.1

Semi-nat. soils

Nat N2fix

Wood exp.

Atmospheric NH3, NOx, N2O

wwt

Leaching & runoff

0.3

2.41.4

0.2

3.8

0.20.2

4.7

6

4

3

2

1

5

7

N fluxes in TgN/yr

Blue-anthropogenic (intentional)Yellow-anthropogenic(unintentional)Green-natural

Sutton et al 2011, European Nitrogen Assessment

55 5

• Reduced dependence on Haber-Bosch N

• Reduced N loss• Increased crop and microbial

diversity• Reduced greenhouse gas

emissions

The value of legumesin farming systems

66 6

Legumes in farming systems

Rotational

Forage

IntercropsCover crops

Main crops

77 7

Capturing the contribution of legumes

Costa et al 2020, Int J Life Cycle Assessment, doi.org/10.1007/s11367-020-01812-x

88 8

Category and Species Site Years Total N2O emissions per growing season or year (kg

N2O-N ha-1)Range Mean

Pure legume standsAlfalfa 14 0.67-4.57 1.99White clover 3 0.50 – 0.90 0.79

Mixed pasture swardGrass-clover 8 0.10 – 1.30 0.54

Legume CropsFaba bean 1 - 0.41Lupin 1 - 0.05Chickpea 5 0.03 – 0.16 0.06Field pea 6 0.38 – 1.73 0.65Soybean 33 0.29 – 7.09 1.58

Mean of all legumes 1.29

Jensen et al., 2013, Agronomy for Sustainable Development

Nitrous oxide emissions from legume crops

99 9

Mitigation: Legume-grass mixtures

• UK pastures have a relatively little leguminous forage

• Increasing grass clover swards would decrease N fertiliser requirements, reducing N2O emissions and production costs with a saving of 0.5 t CO2e/ha/y

Eory et al Marginal Abatement Cost Curve for Scottish Agriculture, 2020

1010

Biologically fixed N can substitute for synthetic N fertilisers

Fuchs et al 2018. Biogeosciences Discussions, 1–43.

1111 11

Crop residues

•A highly uncertain component of the agricultural greenhouse gas inventory•Emissions assumed to represent 1% of N contained in residue inputs•Difficult to assess inputs and emissions associated with them•Likely to be opportunities for mitigation

1212 12

Global production of human edible protein

Leinonen et al, 2019 doi: 10.3389/fsufs.2019.00027

1313 13

The Scottish protein budget

Leinonen et al, 2019 doi.org/10.1016/j.gfs.2020.100386

1414 14

Future of the global N cycle

Fowler et al , 2015

• Large increases in N inputs• Can we increase the proportion of

BNF used to drive global food production?

1515 15

Conclusions

• Global additions of reactive nitrogen exceed sustainable planetary boundaries

• Redirecting more biologically fixed N to support food production could alleviate the N problem

• Legumes alone are not the solution • Legumes also provide wider environmental benefits

and opportunities to address the nitrogen problem

1616 16

Thankyou

We acknowledge funding from: Scottish Government, Committee on Climate Change, Natural Environmental Research Council,Biological and Biotechnological Research Council, DEFRA andThe European Union