Unraveling safe boundaries for net anthropogenic nitrogen inputs: A case study focusing on village scale

The estimation of safe nitrogen (N) boundaries at the village scale is a powerful complement to planetary boundaries and can be used to propose more targeted regional measures. In this paper, net anthropogenic N inputs (NANI) of the village scale is assembled with the depiction of the internal flow of N. The village-scale NANI was estimated for the case area, Liyang, Taihu Basin, eastern China. The safe NANI boundary of the village scale was defined with the help of the N use efficiency (NUE) conceptual framework. The results showed that chemical fertilizer N application played a decisive role in NANI of the village unit. The upper limit of NANI in village planting system was more sensitive to the response of NUE, so the safe NANI boundary at the village scale referring to the above upper limit was determined as N-output = N-input - 327.24 kg ha-1 yr(-1). Additionally, by using scenario analysis, it was found that village units with high NUE could put in more N according to the safe NANI boundary. In turn, higher NANI can be achieved by increasing NUE. The results, which take into account the difference of villages, are informative for village scale diversity N management.