Combining organic and inorganic nitrogen fertilisation reduces N₂O emissions from cereal crops: a comparative analysis of China and Zimbabwe

Agriculture is one of the major sources of nitrous oxide (N2O), a potent greenhouse gas (GHG) whose atmospheric concentrations are estimated to increase with efforts to increase food production through increasing nitrogen (N) inputs. The objective of this study was to quantify N2O emissions from maize (Zea mays L.) and winter wheat (Triticum aestivum L.) fields amended with inorganic, organic N and a combination of both sources (integrated management), in tropical (Zimbabwe) and temperate (China) climatic conditions. In Zimbabwe N2O emissions were measured from maize plots, while in China emissions were measured from maize and winter wheat plots. In Zimbabwe the treatments were; (i) Control, (ii) 60 kg N ha−1 ammonium nitrate (NH4NO3), (iii) 120 kg N ha−1 NH4NO3, (iv) 60 kg ha−1 cattle (Bos primigenius) manure-N, plus 60 kg N ha−1 NH4NO3, (v) 60 kg N ha−1 cattle manure-N, and (vi) 120 kg N ha−1 cattle manure-N. In China, treatments were; (i) Control, (ii) 300 kg N ha−1 Urea, (iii) 92 kg N ha−1 Urea plus 65 kg ha−1 chicken (Gallus domesticus) manure-N, (iv) 100 kg N ha−1 Urea and (v) 100 kg N ha−1 control release Urea. Our results showed that under both temperate and tropical conditions, integrated nutrient management resulted in lower N2O emissions compared to inorganic fertilizers which had higher total and yield-scale N2O emissions. We conclude that by combining organic and inorganic N sources, smallholder farmers in both China and Zimbabwe, and other countries with similar climatic conditions, can mitigate agricultural emissions without compromising productivity.