# Long term phosphorus dynamics in a French organic cropping system network

Claire Jouany, Jean-François Vian, Laetitia Fourrié, Maëlle Le Bras, Blaise Leclerc, Bruno Pontier, Loïc Prieur

► To cite this version:

Claire Jouany, Jean-François Vian, Laetitia Fourrié, Maëlle Le Bras, Blaise Leclerc, et al. Long term phosphorus dynamics in a French organic cropping system network. Congrès annuel de la société Canadienne de science du sol, Jun 2017, Peterborough, Canada. 1 p. hal-01605300

HAL Id: hal-01605300

https://hal.science/hal-01605300v1

Submitted on 5 Jun 2020

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Isaralyon

Une école d'ingénieurs du cœur de la vie

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CREA
Midi-Pyrenees

S
USSAYE
ÉTUDEMENT D'ENGAGEMENT PUBLIC
D'ÉPREUVE & LOISIR

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Institut Technique de
l'Agriculture Biologique

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AGRICULTURES
& TERRITOIRES
CHAMBRE D'AGRICULTURE
DURE ET LOISIR

C. Jouany¹, J.F. Vian², L. Fourrié³, M. Le Bras⁴, B. Leclerc⁵, B. Pontier⁶, L. Prieur⁷

¹: INRA, UMR 1248 AGIR, Université de Toulouse, INP-ENSAT, F-31326 Castanet-Tolosan Cedex

²: ISARA-Lyon, AgroEcology & Environment, 23 rue Jean Baldassini 69364 Lyon

³: Institut Technique de l'Agriculture Biologique, 2485 Route des Pécolets, 26800 Etoile sur Rhône, France

⁴: Chambre d'agriculture, 10 rue Dieudonné Costes, 28008 Chartres Cedex, France

⁵: Institut Technique de l'Agriculture Biologique, 8 rue Costo Caoudo, 84160 Cucuron, France

⁶: EPL La Saussaye 28630 Sours, France

⁷: CREAB, LEGTA Auch-Baulieu, route de Mirande 32020 Auch, Cedex 09, France

Introduction

* P management is a major issue for organic farming (OF) systems. Maintenance of acceptable Soil Test Phosphorus (STP) levels over the long term is considered a key criterion for sustainability evaluation.

* Fertilization strategies are chosen according to the cropping system:

- **High Input Productive systems** : supply of organic fertilizers to compensate for P output and maintain STP at acceptable level.

- **Low Input Autonomous systems** : no fertilization or low level and use of Fabaceae for N supply,

Objectives

To analyze and compare the medium to long term dynamics of STP for OF cropping systems managed under contrasted fertilization regimes.

The study is part of **InnovAB** a national project which aims at testing innovative techniques for soil fertility management in OF systems at several sites in France.

Materials & Methods

La Saussaye

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2010 - 2017; 3 repetitions.
Silty clay loam;
7.3 <pH<8.3; CaCO3 (0.1>12%)

La Hourre

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2002-2016; 2 repetitions
Silty clay loam;
pH = 8.3; CaCO3 (0.1>12%)

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P input = 0
P output = 15.2 +/-9.5 kg ha⁻¹ yr
N input = 0 kg ha⁻¹ yr

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P input = 32 kg ha⁻¹ yr
P output = 15.2 +/-9.5 kg ha⁻¹ yr
N input = 99 +/-16 kg ha⁻¹ yr

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N input = 17 +/-0.0 kg ha⁻¹ yr

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P input = 9.0 +/-0.3 kg ha⁻¹ yr
P output = 11.8 +/-2.2 kg ha⁻¹ yr
N input = 33 +/-2.0 kg ha⁻¹ yr

* Olsen P on 0-30 cm soil horizon; cumulative P budget= Sum of annual P budgets (Input-Ouput)

* Outputs are calculated from grains yield and P content.

Results & Discussion

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<figure><img src="image_14.png" /><figcaption>Figure 1: Relationship between Olsen P and cumulative P budget calculated between 2010 and 2017 (La Saussaye) and 2002-2017 (La Hourre), with cumulative P budget= Sum of annual P budgets (Input-Ouput)</figcaption></figure>

* Annual P budgets (Input-Output, kg P ha⁻¹ yr) were highly contrasted according to sites and system (Mat & Met) : negative for LI systems at both sites and for HI system at La Hourre ; they are positive at La Saussaye for HI system.

* Olsen P dynamics were variable according to sites and P budgets (Fig 1): we observed a continuous decrease with time for both systems at both sites.

* Changes in Olsen P associated with removal of 1 kg P ha⁻¹ differed greatly among sites: 0.04 kg P at La Hourre 0.13 kg P at La Saussaye.

* For low input systems, at both sites, STP decreased with decreasing cumulative P budget ; similar pattern was observed for La Hourre HI where it remained negative ; at that site fertilization regime did not compensate for outputs (Fig.1).

* For La Saussaye HI, although cumulative P budgets remained positive, there was no increase in P Olsen as would be expected (Messiga et al., 2015) (Fig.1).

Conclusion

* Low fertilization regime results in a continuous decrease of STP as soil P deficit increases; P dynamics in low input OF systems is similar to that of conventional ones. The P budget model is validated at both sites.

* The absence of a direct relationship between Olsen P and cumulative P budgets at La Saussaye questions the P fertilizing value of organic manures and / or the capacity of STP to provide adequate diagnostic of Soil Plant Available P when organic manure is supplied on carbonated soils.

Reference

* Messiga et al. (2015) AMBIO. 44:252-262.