Do Metals Increase or Decrease Nitrous Oxide Emissions and Maize Yields from Upland Soils?

Metals, including copper (Cu), iron (Fe), and zinc (Zn), are associated with nitrous oxide (N2O) production processes, such as nitrification and denitrification. This study aimed to elucidate the effects of Cu, Fe, and Zn on N2O emissions and to determine cumulative N2O emission and crop yields from upland soils. Metals were applied at a rate of 20 kg ha(-1) in upland soil supporting maize (Zea mays L.) growth in 2018 and 2019. While the mean value of cumulative N2O emissions across both years was 5.19 kg N2O ha(-1) yr(-1) for the control soil, those of soil treated with Cu, Fe, and Zn were 3.37, 2.48, and 4.82 kg N2O ha(-1) yr(-1), respectively. Ammonium (NH4+) concentration in soil was highest after Fe application, and nitrate (NO3-) concentration was lowest. The copy number of the amoA gene related to NH4+ oxidation was lowest after Fe enhancement, implying that nitrification was inhibited. Furthermore, N2O emission decreased with Cu addition because the copy number of the nosZ gene associated with N2O reduction to N-2 was the highest. Because Cu and Fe decreased yield-scaled N2O emission, the application of either metal could reduce N2O emission per unit area of maize production, suggesting that both metals are beneficial soil amendments for reducing N2O emissions while maintaining maize yield.