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Maintaining high crop yield and meanwhile reducing the risk of environmental pollution are of paramount importance for food security and sustainability. The aims of this study were (i) quantify soil NO₃⁻ -N buffer capacity under wheat-maize cropping system in Northern China, and (ii) establish agronomic optimum and environmentally safe N rates to guide N recommendation for the region. We compiled data of 76 sets of wheat and 73 sets of maize experiments spanning about 20 years, where N rate experiments conducted and soil NO₃⁻ -N content were measured immediately after crop harvest under conventional practice. By applying linear-plateau and plateau-linear models, we computed the soil NO₃⁻ -N buffer capacity, agronomic optimum N rate and environmentally safe N rates. Soil NO₃⁻ -N buffer capacity ranged from 10 to 221 kg ha⁻¹ for wheat season and from 14 to 212 kg ha⁻¹ for maize season …