A method for optimal site-specific nitrogen fertilisation

Yield mapping of crops obtained by harvest with a combine equipped with yield metering device and GPS positioning system, has in recent years, become an important tool in crop management. With respect to nitrogen fertilisation, it is now technically possible to change practices from uniform application to differentiated, site-specific application. The presentation introduces and discusses a method for determining the spatial variation in yield response to nitrogen fertilisation, based on large scale field experiments in 1997-98. The spatial variation in yield response, based on two amounts of uniformly applied nitrogen fertiliser is suggested for generating application maps for optimal sitespecific nitrogen fertilisation. The Optimal method for predicting fertilisation rates seems to give a better background for generating application maps than predictions based on yield maps and the principle of replacement of removed nitrogen. The presented results show that the effect of spatially varied nitrogen fertilisation is reduced at increasing nitrogen input levels, and that this effect increases with decreasing nitrogen input levels.