Effect of nitrogen split application on wild lowbush blueberry productivity and on soil nitrogen

Lafond, J. 2010. Effect of nitrogen split application on wild lowbush blueberry productivity and on soil nitrogen. Can. J. Soil Sci. 90: 189-199. 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-NH4 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 NH4-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 NH4-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 (<30 kg ha -1). However, with higher rates, splitting N between vegetation and production years would maximize fruit yields and reduce environmental risk.