The shape of reactive nitrogen losses from intensive farmland in China

Abstract

Reactive nitrogen (N_r) pollution has changed radically accompanied by severe intensive farming. This pollution further contributes to ecological degradation and climate warming. Despite this recognition, little is known about the spatial pattern of various N_r loss from croplands and corresponding environmental costs. Here, we identified the major pathway of N_r loss based on provincial estimates in 2008 and 2018, and validated by synchronous observation of ammonia volatilization, N runoff and N leaching using historical literature synthesis. We also evaluated environmental costs at provincial scale and detected the influence factors that dominating the pollution swapping among different N_r forms. Our results show that the total N_r loss was 6.28 ± 1.81 and 5.56 ± 2.30 Tg N yr^-1 for Chinese croplands in 2008 and 2018. Ammonia volatilization, which accounted for more than half of the total N_r at the national scale, was proven to be the major N_r loss for two-thirds of the provinces and 80 % of the field observations. The contribution of runoff, which is dominant by precipitation, soil clay content and CEC, was gradually smaller than that of leaching from southeast to northwest. Ammonia and nitrous oxide contributed of 59.3 % ∼ 65.4 % of TN_r but 80.9 % ∼ 81.5 % of total environmental damage caused by N_r in China. The use of nitrification inhibitors and straw return indicated pollution swapping among various N_r forms. This study emphasizes that the future practices to reduce total N_r loss need to account for local environmental conditions and have pollution swapping in sights.

Keywords: Environmental damage cost; Pollution swapping; Reactive nitrogen loss; Sustainable N management.