Surface N balances and reactive N loss to the environment from global intensive agricultural production systems for the period 1970–2030

Data for the historical years 1970 and 1995 and the FAO-Agriculture Towards 2030 projection are used to calculate N inputs (N fertilizer, animal manure, biological N fixation and atmospheric deposition) and the N export from the field in harvested crops and grass and grass consumption by grazing animals. In most industrialized countries we see a gradual increase of the overall N recovery of the intensive agricultural production systems over the whole 1970–2030 period. In contrast, low N input systems in many developing countries sustained low crop yields for many years but at the cost of soil fertility by depleting soil nutrient pools. In most developing countries the N recovery will increase in the coming decades by increasing efficiencies of N use in both crop and livestock production systems. The surface balance surplus of N is lost from the agricultural system via different pathways, including NH3 volatilization, denitrification, N₂O and NO emissions, and nitrate leaching from the root zone. Global NH₃-N emissions from fertilizer and animal manure application and stored manure increased from 18 to 34 Tg·yr^?1 between 1970 and 1995, and will further increase to 44 Tg·yr^?1 in 2030. Similar developments are seen for N₂O-N (2.0 Tg·yr^?1 in 1970, 2.7 Tg·yr^?1 in 1995 and 3.5 Tg·yr^?1 in 2030) and NO-N emissions (1.1 Tg·yr^?1 in 1970,1.5 Tg·yr^?1 in 1995 and 2.0 Tg·yr^?1 in 2030).