VARYING APPLICATION OF NITROGEN-FERTILIZE R ACCORDING TO LOCAL-RESOURCES - EXPERIENCE FROM DANISH TRIALS

Throughout the years the Department of Plant Production in Denmark has calculatet the nitrogen demand for different crops. When calculating the nitrogen demand in different parts of fields the same methods are used in principle. The N-min-method and the nitrogen module of the Dan ish Integrated Farm Management System are developed to calculate the n itrogen demand. The calculated nitrogen demand was compared with the m easured nitrogen demand in 197 fertilizer trials in the period 1987-19 95. In general, there was good agreement between measured and calculat ed data The calculated nitrogen demand on a field scale is used as inp ut when the nitrogen demand in different part of a field is. When diff erentiating between different parts of the fields, soil type and expec ted yield are important parameters. Experience over 3 years in 4 field s divided into subfields shows that the economic outcome by differenti ating nitrogen fertilizer in winter wheat was between 25 and 50 DM. Fu rthermore, it turned out that it is possible to reduce the impact on t he environment when the application of fertilizers, lime, herbicides e tc. is differentiated between different parts of the field. There is s till a need to evaluate how fields are divided into subfields in the m ost appropiate and correct way.