Historical Changes in Fertilizer-Induced Soil Nitrogen Losses from Upland Grain Crops and Impacts of Climate Change

Fertilizer nitrogen (N) inputs into agricultural soils will be partially lost as reactive N (Nr) to the environment, resulting in a global N cascade and environmental concerns. Understanding historical trends of soil Nr losses over decades is currently urgently required to target future mitigation strategies under climate change. Here, we develop random forest (RF) models to reveal the historical changes of soil Nr losses from global maize and wheat cultivation over 1961-2020 and their future mitigation potentials. Global mean factors of fertilizer N lost as Nr (F-Nr) to the environment decreased from 27 to 30% in 1961 to 20-25% in 2020. However, this trend contrasts with the estimated total soil Nr losses from maize fields, which have shown a continuous increase from 1.0 to 6.0 Tg N yr^-1 over the past six decades. High-income regions and some rapidly developing countries are identified as hotspots of soil Nr losses. Site-specific N rate strategies by incorporating future climate impacts are projected to reduce 26-30% of soil Nr losses from global maize and wheat production. Our findings emphasize the need to incorporate the effects of climate change into the improved strategies for alleviating Nr pollution caused by agricultural fertilization.