Couhins - Nouvelle Aquitaine (Gironde)

Couhins has been initiated in 1974 (ended between 1980 and 1998)

The objectives are to determine the lasting effects of sewage sludge, composted household waste or cattle manure applications on soil-plant tranfert of metal trace elements. The Agronomy unit of Bordeaux had set up the follow-up of 3 long-term experimental trials that are currently in resilience which means it is possible to evaluate agro-system evolution after the arrest of OR applications.

• Location : Couhins - Nouvelle Aquitaine (Gironde)
• Administrator unit : UMR ISPA INRA - Bordeaux Sciences Agro (https://www6.bordeaux-aquitaine.inra.fr/ispa)
• Supervisor and contact : Valérie Sappin-Didier

Treatments

Treatments performed on the 3 trials are presented bellow :

"Ambarès" trial (1974-1993)

The field experimental design is a complete randomized block experiment (5 blocks, parcels of 18 m²) with the following treatments :

• Semi-dehydrated biological sewage sludge*, 10 t MS / ha / year (B10)
• Semi-dehydrated biological sewage sludge, 100 t MS / ha / 2 years (B100)
• Cattle manure, 10 t MS / ha / year (F)
• Control : mineral fertilizer (T)

* Sewage sludge with high concentrations of Zn, Mn and Cd.

Organic amendments for this trial were stopped in 1993 for 10T sludge (B10) and manure, and in 1992 for 100T sludge (B100). This was justified by the excessive values ​​obtained for cumulative inputs since 1974 (200 t DM / ha / year for 10T Manure and Sludge, and 1000 t DM / ha / 2 year for 100T sludge) and a scientific concern to study the fate of trace elements in the soil over time.

"Louis Fargue" trial (1976-1980)

The field experimental design is a complete randomized block experiment (5 blocks, parcels of 18 m²) with the following treatments :

• Dehydrated digested biological sewage sludge**, 10 t MS / ha / year (B10)
• Dehydrated digested biological sewage sludge, 100 t MS / ha / 2 years (B100)
• Cattle manure, 10 t MS / ha / year (F)
• Control : mineral fertilizer (T)

** Sewage sludge containing Cd and Ni concentrations above the current regulations.

Organic amendments for this trial were stopped in 1980 following visible phytotoxicity on maize crops.

"Saint Denis de Pile" trial (started in 1981-1998)

The field experimental design is a complete randomized block experiment (4 blocks, parcels of 14 m²) with the following treatments :

• Sewage sludge***, 10 t MS / ha / year, 0-400 kg /ha ammonium nitrate (B0, B50, B100, B200, B400)
• Composted household waste, 10 t MS / ha / year, 0-400 kg /ha ammonium nitrate (C0, C50, C100, C200, C400)
• Control : mineral fertilizer, 0-400 kg /ha ammonium nitrate (T0, T50, T100, T200, T400)

*** Semi-dehydrated biological sewage sludge with high concentrations of Zn, Mn and Cd.

Figure : Plan of the experimental device Couhins (Sappin-Didier)

Site management

"Ambarès" and "Louis Fargue" trials : maize (1974/1976-1996, 1998-2000), potato (1997), lettuce (2001), wheat (2002)

"Saint Denis de pile" trial : potato (1981-1996, 1998-1999), maize (1997), carrot (2000), lettuce (2001), wheat (2002)

The cultural practices are identical for each parcel of the 3 trials. They include tillage (burial of organic residues and / or waste input, preparation of the seedbed), fertilization, sowing, weeding, irrigation, phytosanitary treatment, and harvesting.

pedo-climatic context

These devices are developed on alluvial gravel sandy texture (Dystric Luvisols) on the field of Couhins (Gironde). The initial characteristics of the plowed layer are:

• pH : 5,3
• CEC : 3,28 cmol + / kg
• Organic carbon content : 1,35 %
• Granulometry : 4 % clays, 7 % silts, 89 % sands
• Climate type : oceanic
• Average annual temperature : 13,7 °C
• Average annual rainfall : 720 m

See next => La Bouzoule