The aim of the present work was to assess and compare energy inputs and outputs of various crop managements in 2011–2012. Two main crops on arable land and three permanent grasslands were investigated. Silage maize (Zea mays L.) and winter wheat (Triticum aestivum L.) were grown on lowland, whilst two semi-natural grasslands and grassland infested by tufted hair-grass (Deschampsia caespitose (L.) P. Beauv) were located in mountainous regions of Slovakia. In these crops and grasslands the dry matter yield was measured and subsequently the supplementary energy, energy gain and unifying energy value – tonne of oil equivalent (TOE) – were calculated. Silage maize with 233.37 GJ*ha-1 has provided the highest energy gain. In the group of grasslands, grassland infested by tufted hair-grass has offered the highest energy gain (59.77 GJ*ha-1). And this grassland had the lowest requirement on the supplementary energy (3.66 GJ*ha-1), contrary to silage maize with highest one (12.37 GJ*ha-1). The total energy potential of the crop biomasses was confronted with energy consumption in Slovakia. Winter wheat has the biggest energy potential, but it could cover only 19.6% and 11.3% total consumption of electricity or natural gas, respectively. Large area of permanent grasslands and their spatial location make them an important energy reservoir for bioenergy production. But, it is not possible to replace all consumed fossil fuels by bioenergy from these tested renewable energy sources.