According to the OECD-Eurostat methodology (2013), the nitrogen (N) budget in agriculture represents the difference between the input of N on agricultural land and the output of N from agricultural land with crop yields. We distinguish between gross and net nitrogen budget. Gross nitrogen budget is the difference between total input and output of nitrogen. Gross nitrogen budget is represented by the following sources: N excreted by farm animals, N in mineral fertilizers, biological fixation of N by legumes, deposition of atmospheric N, N from other organic fertilizers (compost, sewage sludge ...) and N from seeds and planting material. Output represent nitrogen uptake of harvested crops. The net nitrogen budget refers mainly to the available N for crop growth (net input). Net nitrogen budget is calculated by subtracting N that is released into the atmosphere (from animal sheds, manure storage tanks, during grazing, during and as a result of fertilising with mineral, animal and other organic fertilisers, during the decomposition of crop residues in soil and as a result of cultivation of histosols) from the gross nitrogen budget. This is N that is released into the atmosphere through emissions of ammonia (NH₃) nitrous oxide (N₂O) and nitrogen oxides (NO_x). The gross and net nitrogen budget were expressed in tonnes N at the national level and in kilograms N per hectare of utilized agricultural area. Data for the period 1992–2017 are presented. The indicator also presents the structure of input and output of N and comparison with EU countries (EU-28).

In the period 1992–2017, the total nitrogen input to agricultural land was reduced from 89,850 tonnes of N to 75,197 tonnes of N (16%). Input of nitrogen per hectare of utilised agricultural area was also reduced, from 162 kg N/ha to 156 kg N/ha (by 4%). The main sources of nitrogen are livestock manure and mineral fertilisers. Their contribution to nitrogen input in period 1992-2017 was 48% and 39%. Other sources are less important: atmospheric deposition contributes 10%, biological fixation by legumes 2%, seeds and seedlings material 0.4%. The main reason for the reduction of N input is the 30% reduction in the consumption of N from mineral fertilizers. The reduction of utilised agricultural area resulted in reduced input of atmospheric deposition (by 13%) and input of nitrogen through seeds and seedlings material. In the period 1992–2017, input of nitrogen through biological fixation increased by 90% due to an increase in the cultivation of legumes.

Nitrogen output varied considerably in the period 1992–2017, amounting to between 28,752 and 55,437 tonnes of N per year. The output of N per hectare of agricultural land was between 52 and 116 kg per year. Such great differences are a consequence of different weather conditions, as nitrogen output is notably lower in dry years when crops yields are lower. The main source of nitrogen output is permanent grassland (64%), followed by grain fields (19%) and green fodder from arable fields (12%). Other crops (root crops, tubers, fruit, vegetables, legumes and industrial plants) combined contribute 5% of nitrogen output.

In the period 1992-2017 the gross nitrogen budget was between 42 and 110 kg N/ha. The highest (more than 80 kg N/ha) were recorded in the dry years 1992, 1993, 2000, 2001 and 2003, when crop yields were reduced which resulted in lower nitrogen output. The trend analysis clearly revealed that gross nitrogen budget in the period 1995–2017 was decreasing (by 1.5 kg per year, 44% over the entire period). Net nitrogen budget was also decreasing (by 1.4 kg per year, 72% over the entire period). Lower nitrogen budgets indicate better nitrogen management and, consequently, lower emissions of nitrogen compounds into the environment. While 52% of input nitrogen was taken from agricultural land in the period 1992–2003, the percentage increased to 66% in the period 2004–2017, even exceeding 70% in certain years. In the last five-year period (2013–2017), average gross nitrogen budget was 52 kg N/ha, while net nitrogen budget was 21 kg N/ha.

In the period 2006-2015, Slovenia showed a slightly higher average gross nitrogen budget (54 kg N/ha) than EU Member States (50 kg N/ha). This is a consequence of the large percentage of grassland in the structure of agricultural land and the associated livestock production, characterized by extensive emissions of nitrogen compounds into the air.