Nicolas MARRONBernard AMIAUD

Daniel EPRONErwin DALLÉ

Alexandre LAFLOTTESéverine PIUTTI

European Agroforestry ConferenceMay 23-25, 2016 – Montpellier, France

Present geopolitical and environmental world context:

- Rarefaction of fossil fuels

- Needs to reduce CO2 emissions

Promotion of renewable energy sources

Biomass

Forest = first supplier currently

+ Short Rotation Coppice (SRC) plantations on agricultural lands

Introduction

1

Soil fertility

Profitability

Technical procedure

Environment

Biodiversity/ Landscape

Currently not attractive because not optimized

Tree plantations dedicated to biomass production

Introduction of nitrogen

fixators

SRC

2

3

Introduction of N fixators, woody or herbaceous

Tree plantations dedicated to biomass production

2 m

2.5 m

Poplar

CerealsAlfalfa

Alder

5 m

Po

pla

r

Ald

er

Alfalfa / Clover…

Po

pla

r

4

Mixture poplar / alfalfa

Poplarmonoculture

Mixturepoplar / alder

NN N

Our hypotheses

Mixture plantations introducing nitrogen fixators

5

Mixture poplar / alfalfa

Poplarmonoculture

Mixturepoplar / alder

Po

pla

r

Ald

er

Alfalfa / Clover…

Po

pla

r

NN N

15N labelling

Leaf gas exchanges

Canopy description / LAI

Root profiles

Growth / Biomass

Our hypotheses and the ways to test them

Mixture plantations introducing nitrogen fixators

6

Amance

Nancy

The experimental agroforestry plantation: location

Mixture plantations introducing nitrogen fixators

7

Power line

Block

2

Block

1

Block

3

N

The experimental agroforestry plantation: layout

Mixture plantations introducing nitrogen fixators

3.5 ha – 3500 trees – 100 tree lines

The experimental agroforestry plantation: maintenance

Mixture plantations introducing nitrogen fixators

8

- Instrumentation to monitor soil and weather conditions

- Protection of trees against game + mulching

- Weed control (mechanical, chemical)

- Watering during summer 2015

9

Already some undesirable treatment effects!

Mixture plantations introducing nitrogen fixators

MonocultureTree

mixtureAgroforestry

350

300

250

200

150

100

50

0

MonocultureTree

mixtureAgroforestry

Alder Poplar

Two-year old tree heights (cm)

Species ***Treatments ***

S×T ns

10

Already some undesirable treatment effects!

Mixture plantations introducing nitrogen fixators

Wheat yield in 2015

Mixture with alder: 40,3 ± 2,5 quintal ha-1

Monoculture: 49,0 ± 3,6 quintal ha-1

11

Aim: to determine the amount

of nitrogen fixed by the leguminous

Method: Symbiotic nitrogen fixation

Isotopic dilution: increase of soil 15N signal

with an input of a labelled fertilisant

(ammonium sulfate (15NH4)2SO4)

%Ndfa= 100 1 −𝑥𝐸

𝑙𝑒𝑔

𝑥𝐸𝑛𝑜𝑛

−𝑙𝑒𝑔

(Fried & Middelboe, 1977)

𝑥𝐸 (excess in 15N) = 15N × 100/(15N + 14N) − 0.003663

Transfers

Pnonleg(atm)= 1 − (𝑥𝐸𝑛𝑜𝑛 − 𝑙𝑒𝑔 𝑚𝑖𝑥𝑡𝑢𝑟𝑒 /𝑥𝐸𝑛𝑜𝑛 − 𝑙𝑒𝑔 𝑝𝑢𝑟𝑒)

Pnonleg(leg)= (𝑥𝐸𝑛𝑜𝑛 − 𝑙𝑒𝑔 𝑝𝑢𝑟𝑒 − 𝑥𝐸𝑛𝑜𝑛 − 𝑙𝑒𝑔 𝑚𝑖𝑥𝑡𝑢𝑟𝑒) / (𝑥𝐸𝑛𝑜𝑛 − 𝑙𝑒𝑔 𝑝𝑢𝑟𝑒 − 𝑥𝐸𝑙𝑒𝑔 𝑚𝑖𝑥𝑡𝑢𝑟𝑒)

(Chalk & Smith, 1994)

Percentage of 15N in excess

Percentage of N derived from the

atmosphere

N proportion in the non fixing species coming from

the biological N fixation

N proportion in the non fixing species coming

from the N fixing species