The invention relates to a method for optimal sulphur fertilisation of cultivated plants. The method involves time and site-specific determination of the additional sulphur requirement before and during the growing period based on the sulphur requirement calculated by means of the target yield and a change caused in this by environmental conditions. When deficiency has been observed and possibly verified by experimental measurements, the cultivator is given a recommendation of additional sulphur fertilisation. The sulphur balance can be determined by means of an expert system.
