La lixiviation d’azote nitrique dans les rotations céréalières avec colza : un diagnostic à partir de l’analyse de résultats d’expérimentations pluriannuelles et de modélisations

Nitrate leaching was measured during 6 years in a crop rotation including oilseed rape (OSR) and winter wheat in two field trials, on two rendzina soils differing by their water content, in Le Magneraud (West of France) and Martincourt (East of France). Results show that nitrate losses are variable within the year and drainage: between 20 and 95 kgN.ha–1.an–1. When the soil remains without cover crop after OSR, losses under wheat following OSR are definitely higher than under OSR following wheat: respectively 54.1 kgN.ha–1.an–1 and 14.8 kgN.ha–1.an–1 during the first three years in Le Magneraud. Results even show that nitrate losses differed according to N strategy management. Among the treatments of nitrogen management, the least losses are observed with optimized fertilization plus OSR volunteers used as cover crop between OSR and wheat; and the highest losses are observed with high fertilization without OSR volunteers as catch crop : respectively in Le Magneraud (second phases of three years) 29.9 and 61.1 kgN.ha–1.an–1, and at Martincourt 43.0 and 61.4 kgN.ha–1.an–1 on average. Simulations realized with LIXIM and DEAC models for new years, soils and regions, show the same trend that experimental results: nitrate losses are higher under wheat after OSR, and the high performance cropping systems are based on optimized N fertilization management of OSR and the catch of nitrate at the end of summer by OSR (after wheat) or its volunteers (before wheat).