Soil is a non-renewable resource, so we should take care of it. High quality food with sufficient yield for a growing human population can be produced only if plant nutrients are added to the soil by fertilisers to increase soil fertility, having in mind that the fertilisers have to be used economically, with the aim of raising the nutrient content available in the soil in order to meet plants’ needs. The goal of the present investigation was to determine the effect of application of organic and mineral fertilisers as well as the effect of research environment on micronutrient (Fe, Mn and Zn) content in red beet root. A field trial (2003–2005) was set up in a hilly part of Croatia according to the Latin square method, with four types of fertilisation (control, 50 t stable manure ha-1, 500 and 1000 kg NPK 5-20-30 ha-1). After digestion of plant material with concentrated HNO3, iron, manganese, and zinc were determined by an atomic absorption spectrophotometer (AAS). The highest average red beet root micronutrient contents (270 mg Fe kg-1 in dry matter, 96 mg Zn kg-1 in dry matter, and 53 mg Mn kg-1 in dry matter) were determined in the first research environment (Brašljevica in 2003) with low potassium soil content. There was a general decreasing trend in contents of the studied micronutrients (Fe, Mn and Zn) with NPK 5-20-30 fertilisation (and by application of high doses of potassium), certainly due to antagonistic activity with potassium. It is suggested to fertilise with both 500 kg NPK 5-20-30 ha-1 and microelement fertilisers.