# Do agricultural practices impact carbon, nitrogen and phosphorus stoichiometry in plants and soils on the long-term?

Fabien Ferchaud, Bruno Mary, Frida Keuper, Alain Mollier, Pascal Denoroy, Christian Morel, Anne Budynek, Sabine Houot, Claire Jouany, Mickael Hedde, et al.

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## To cite this version:

Fabien Ferchaud, Bruno Mary, Frida Keuper, Alain Mollier, Pascal Denoroy, et al. Do agricultural practices impact carbon, nitrogen and phosphorus stoichiometry in plants and soils on the long-term?. 20th Nitrogen Workshop, Jun 2018, Rennes, France. 472 p. hal-02735020

HAL Id: hal-02735020

https://hal.inrae.fr/hal-02735020

Submitted on 2 Jun 2020

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Distributed under a Creative Commons Attribution 4.0 International License
# Do agricultural practices impact carbon, nitrogen and phosphorus stoichiometry in plants and soils on the long term?

**Fabien FERCHAUD**, Bruno MARY, Frida KEUPER, Alain MOLLIER, Pascal DENOROY, Christian MOREL, Anne GALLET-BUDYNEK, Sabine HOUOT, Claire JOUANY, Mickaël HEDDE, Philippe HINSINGER, Christophe JOURDAN, Isabelle BERTRAND

FlexStoechio project

Agrolmpact

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# Introduction

## Background

* ✓ Stoichiometry is the ratio of elements in organisms and environment

* ✓ Stoichiometry was mainly applied in natural environments

* ⇒ In terrestrial environments, ratios are rather constraints at the biome level

* ⇒ In soil, at the global scale, C:N ratios are often more constraints than C:P or N:P ratios
(Xu et al., 2013; McGroddy et al., 2014)

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> However, the effect of agricultural practices on the soil and plant stoichiometry has received less attention
# Introduction

* Stoichiometry : what does it imply?

✓ Widespread interest in increasing soil carbon stocks (e.g. 4 per 1000 initiative) => a possible “hidden cost” due to the need of inorganic nutrients? (Richardson et al., 2014; van Groenigen et al., 2016)

* Objectives

- To evaluate the range of flexibility of C:N:P ratios in soils and plants for various arable cropping systems

- To quantify the effect of agricultural practices (including long term fertilisation) on these ratios and their evolution

* Hypothesis

- Stoichiometric relationships in soils and plants can be altered by agricultural practices
# Methods

* Collecting long term field experiments data

✓ 8 long term field experiments comparing different levels of N or P inputs in arable cropping systems and providing data on plants and soils C, N and P contents

✓ Dataset completed by additional analyses when needed

**Resulting dataset:**

- 7900 plant data: yield, C, N and P content (grains)

- 2600 soil data : organic C, total N and total P content (topsoil)

* Analyzing C, N, P contents and their stoichiometry in plants and soils in relation to agricultural practices
# The sites and trials

<table><thead><tr><td>Site</td><td>Name and location</td></tr></thead><tbody><tr><td>1</td><td>La Cage (Versailles)</td></tr><tr><td>2</td><td>SOERE QualiAgro (Feucherolles)</td></tr><tr><td>3</td><td>SOERE ACBB</td></tr><tr><td>4</td><td>Biomass & Environment (Estrées-Mons)</td></tr><tr><td>5</td><td>Auzeville (near Toulouse)</td></tr><tr><td>6</td><td>Mant (near Pau)</td></tr><tr><td>7</td><td>Tartas - Carcarès Sainte-Croix (near Dax)</td></tr><tr><td>8</td><td>Pierroton (near Bordeaux)</td></tr></tbody></table>

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# The sites and trials

<table><thead><tr><td>Site</td><td>Name and duration</td><td>Tested agricultural practices</td></tr></thead><tbody><tr><td>1</td><td>La Cage<br/>1998-2014 (16 years)</td><td>4 arable cropping systems: conventional, low input, conservation agriculture, organic farming</td></tr><tr><td>2</td><td>SOERE QualiAgro<br/>1998-2013 (15 years)</td><td>Organic waste products (4 types) * N fertilisation (2 rates)<br/>Wheat-maize rotation</td></tr><tr><td>3</td><td>SOERE ACBB<br/>2009-2015 (6 years)</td><td>4 treatments: conventional, reduced tillage, crop residue removal, reduced N fertilisation<br/>Arable cropping system</td></tr><tr><td>4</td><td>Biomass & Environment<br/>2006-2016 (10 years)</td><td>Crop type (perennials vs annuals) * N fertilisation (2 rates)</td></tr><tr><td>5</td><td>Auzeville<br/>1969-2017 (48 years)</td><td>P fertilization (superphosphate): 0, 11, 22 and 33 kg P ha<sup>-1</sup> yr<sup>-1</sup><br/>Arable cropping system</td></tr><tr><td>6</td><td>Mant<br/>1975-1992 (17 years)</td><td>P fertilization (superphosphate): 0, 27, 79 kg P ha<sup>-1</sup> yr<sup>-1</sup><br/>Continuous irrigated maize</td></tr><tr><td>7</td><td>Tartas<br/>1972-2004 (32 years)</td><td>P fertilization (superphosphate): 0, 44, 96 kg P ha<sup>-1</sup> yr<sup>-1</sup><br/>Continuous irrigated maize</td></tr><tr><td>8</td><td>Pierroton<br/>1995-2015 (20 years)</td><td>P fertilization (superphosphate): 10, 15, 20, 40, 80 kg P ha<sup>-1</sup> yr<sup>-1</sup><br/>Continuous irrigated maize</td></tr></tbody></table>
# C, N and P relationships in plants (grains)

* Ranges of C:N, C:P and N:P ratio observed by species

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* Large variability particularly for C:P and N:P ratios

* Mainly due to N and P variations (C ~ constant)

* Strong differences between species

⇒ We focused on main crops (wheat in N trials, maize in P trials) to analyse the effects of agricultural practices
# Impact of N fertilisation on yield and ratios

## N fertilisation on wheat:

* ✓ increased **yield** (++)

* ✓ decreased **C:N** ratio

* ✓ Increased **N:P** ratio

* • No significant effect on **C:P** ratio

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Different letters: p< 0.05
# Impact of P fertilisation on yield and ratios

## P fertilisation on maize:

* ✓ increased **yield** (+)

* ✓ decreased **C:P** and **N:P** ratios

* Lower **C:N** ratios in P0

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Different letters: p< 0.05
Relationships between C, N and P contents

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* C, N and P contents in soils were closely linked

* At the site level, relationship between C and N was more constraint than between C and P or N and P

* A strong site effect was observed

⇒ necessity to focus on **temporal changes** in contents or ratios to evaluate impacts of agricultural practices
Temporal evolution of ratios in soil

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* C:N ratio evolution was site specific and not influenced by treatments, excepted the input of organic waste products

* C:P and N:P ratios evolution was influenced by P inputs and organic waste products
Changes in soil C, N and P contents

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* Organic products changed C:N ratio by increasing more rapidly than N content in soil

* Organic products also increased more rapidly C and N than P contents (except for one type of product)
Changes in soil C, N and P contents

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* Organic fertilisers changed C:N ratio by increasing more rapidly than C than N content in soil

* Organic products also increased more rapidly C and N than P contents (except for one type of product)

* P inputs changed C:P and N:P ratios mainly by changing P content
# Effects of practices on C, N and P in soil

## Summary

<table><thead><tr><th></th><th>N+ vs N-</th><th>P+ vs P-</th><th>Organic waste prod. vs mineral fert.</th></tr></thead><tbody><tr><td>C content</td><td>↑ (2 sites /4)</td><td>↑ (1 site /4)</td><td>↑↑</td></tr><tr><td>N content</td><td>↑ (2 sites /4)</td><td>↑ (1 site /4)</td><td>↑↑</td></tr><tr><td>P content</td><td>NS</td><td>↑ (4 sites /4)</td><td>↑↑ or ↑ or =</td></tr><tr><td>C:N</td><td>NS</td><td>NS</td><td>↑ or =</td></tr><tr><td>C:P</td><td>NS</td><td>↓ (4 sites /4)</td><td>↑ or ↓</td></tr><tr><td>N:P</td><td>NS</td><td>↓ (4 sites /4)</td><td>↑ or ↓</td></tr></tbody></table>
# Conclusion and prospects

* Long term **N and P fertilisation** treatments induced **differences in crop grain yields and in ratios** (mainly C:N and N:P for N fertilisation ; C:P and N:P for P fertilisation)

* Long term **P fertilisation** treatments induced **strong differences in C:P and N:P ratios in soil**, mainly due to variation in P content

* **C:N stoichiometry in soil was more constraint** and not affected by N and P inputs (except when organic products were applied)

* However, **significant changes in C:N ratio with time** were observed in several sites

## Prospects:

* To analyse changes in contents and ratios in soil in relation with N and P budgets (inputs – exports) and with C inputs
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Thank you for your attention

We thank the INRA Division Environment and Agronomy for funding this project.

We thank the students involved in this work:
Jocelyn Carré and Emilie Swaenepoel