Fractionnement de la fertilisation azotée dans la production du bleuet nain sauvage et suivi de l’azote du sol

In wild lowbush blueberry production, fertilizers are applied in the spring of the vegetative year. To increase fertilizers efficiency and to reduce environmental losses, fertilizer split applications between vegetative and production year have been proposed. The objectives of this project were to determine the effect of split application of the nitrogen (N) in the vegetative and production year on the wild blueberry production and on soil mineral N in six blueberry fields located in Saguenay-Lac-Saint Jean (Quebec, Canada). Four rates of ammonium sulfate were applied in the spring of the vegetative year (0, 30, 60 and 90 kg ha -1 ). These same rates were applied in the spring of the vegetative (50%) and production (50%) years. The 30 kg N ha -1 rate was also applied only in the production year. For all sites, maximum fruit yields (3800 kg ha -1 ) were obtained with 62 kg N ha -1 . However, the maximum rate ranged from 25 to 90 kg N ha -1 according to the sites. Applying N in the vegetative and production years had comparable fruits yields to those obtained with the fertilizer applied only in the vegetative year. One month after N application, the amount of N-NH 4 in the soil profile increased by 4 to 38 kg ha -1 compared with the control. Split N application reduced by 55 to 76% the amount of NH 4 -N in soil layers only in the vegetative year. Soil nitrate increased with N rates at the end of the growing season, indicating that a part of NH 4 -N was nitrified and can be potentially leached the under root zone. According to the various maximum N rates obtained and N fertilizer impacts on soil N mineral, there would be no agronomic or environmental benefit to splitting low rates (