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

Increasing environmental losses of N

Global nitrogen (N) budgets for intensive agricultural systems are compiled for a 0.5 by 0.5 degree resolution. These budgets include N inputs (N fertilizer, animal manure, biological N fixation and atmospheric N deposition) and outputs (N removal from the field in harvested crops and grass and grass consumption by grazing animals, ammonia volatilization, denitrification and leaching). We use data for the historical years 1970 and 1995 and a projection from FAO for 2030 to study changes in the recovery of N and the different loss terms for intensive agricultural systems. The results indicate that the overall system N recovery and fertilizer use efficiency slowly increased in the industrialized countries between 1970 and 1995, the values for developing countries have decreased in the same period.

For the coming three decades our results indicate a rapid increase in both the industrialized and developing countries. High values of >80% for fertilizer use efficiency may be related to surface N balance deficits, implying a depletion of soil N and loss of soil fertility. The projected intensification in most developing countries will cause a gradual shift from deficits to surpluses in the coming decades. The projected fast growth of crop and livestock production, and intensification and associated increase in fertilizer inputs will cause a major increase in the surface N balance surplus in the coming three decades. Despite the improvement of the efficiency, it is clear that the fast increase of production and intensification will almost inevitably lead to increasing environmental losses of N. Depending on the characteristics of the system, there will be increasing emissions of NH₃ to air, nitrate leaching to groundwater, and release of gaseous N oxides produced during denitrification which play an important role in greenhouse warming (N₂O) and ozone chemistry (NO).