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 surplus is the difference between total input and output of nitrogen. Gross nitrogen input 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 (composts, digestates, sewage sludges ...) and N from seeds and planting material. Output represents nitrogen uptake of harvested crops.

The net nitrogen surplus refers mainly to the available N for crop growth (net input). Net nitrogen surplus is calculated by subtracting N that is released into the atmosphere (from animal houses, manure stores, 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 surpluses were expressed in tonnes N at the national level and in kilograms N per hectare of utilized agricultural area. Data for the period 1992–2023 are presented. The indicator also presents the structure of input and output of N and comparison with selected EU countries in the period 2010–2021.

The main sources of nitrogen input in agriculture are livestock manures (48%) and mineral fertilizers (39%). Atmospheric deposition contributes 10% of nitrogen input, biological fixation by legumes 3%, seeds and seedlings 0.4% and other organic fertilizers 0.2%. Between 1992 and 2023, total nitrogen input decreased by 17%. The main reason is a 27% reduction in nitrogen consumption from mineral fertilizers. Nitrogen input from livestock manure decreased by 14%. Due to the reduced areas of utilized agricultural area, the input of atmospheric nitrogen and by seeds and seedlings decreased by 11%. Due to the increased extent of legume production, biological nitrogen fixation increased by 136%. Nitrogen input per hectare of utilized agricultural area decreased by 6%, mainly due to a 18% decrease in nitrogen input from mineral fertilizers per hectare of utilized agricultural area.

In the period 1992–2023, the annual nitrogen output by crops varied from 52 to 122 kg per ha. The variation was mainly due to weather conditions, as nitrogen output was notably lower in dry years. Nitrogen output per ha of utilized agricultural area increased by 43% during this period. The main source of nitrogen output was permanent grassland (64%), followed by cereals (19%) and forage crops (12%). Other crops (roots, tubers, fruits, vegetables, legumes and industrial plants) together contributed 5% of total nitrogen output.

In the period 1992-2023 the gross nitrogen surplus varied between 29 and 111 kg per ha. The highest surpluses (more than 80 kg N/ha) were recorded in the dry years 1992, 1993, 2000, 2001 and 2003, when outputs with crop yields were reduced. The trend analysis clearly revealed that gross nitrogen surplus in the period 1992–2023 decreased by 1.4 kg per ha per year or by 54% over the entire period. Net nitrogen surplus decreased by 1.2 kg per ha per year or by 85%. The lower nitrogen surplus was mainly due to a 43% increase in nitrogen uptake by crops and a 6% decrease in nitrogen input per hectare of utilized agricultural area. Lower nitrogen budgets indicate better nitrogen management and, consequently, lower emissions of nitrogen compounds into the environment. While 55% of total nitrogen input was taken from agricultural land by crops in the period 1992–2007, the percentage increased to 69% in the period 2008–2023.

A realistic comparison of the gross nitrogen surplus with other EU Member States is not possible. Data is only available for 15 countries, with no data available for the countries that had the largest surpluses in the past (Cyprus, the Netherlands, Malta, Belgium, Luxembourg and Denmark, details in KM022 The Nitrogen Budget in Agriculture, 2021 version). Among the countries with available data, Slovenia belongs to a group of five countries with surpluses of 40–45 kg N/ha (Slovenia, Slovakia, Portugal, Hungary and Spain), which follow the group with surpluses above 55 kg N/ha (Czech Republic, Germany, Croatia, Italy).