Effect of carbon rate and type amended with ammonium or nitrate on nitrous oxide emissions in a strong ammonia oxidation soil

Purpose The work aimed to (1) better understand how C rate and type affecting N2O emissions when combined application with different N forms in a strong ammonia oxidation soil, (2) further explore the tradeoff and mechanism of C availability to N transformations, and (3) provide evidence for making targeted N2O mitigation measures in these kinds of agricultural soils. Materials and methods The soil was collected from a typical farmer's field in Quzhou, Hebei province, China, classified as calcareous Cambisols (FAO classification system) and characterized with high pH (7.72), low organic C (9.1 g kg(-1)), and a strong ammonia oxidation potential. Two microcosm incubations were conducted in laboratory under 20 degrees C and 70% WFPS (water-filled pore space), and the soils were amended with different glucose rates (0, 0.5, 1.0, 2.0, 4.0 mg C kg(-1)) in Exp I, and with different C sources (glucose, pectin, starch, cellulose, lignin, straw) in Exp II, meanwhile with NH4+ or NO3--based fertilizer addition. 480 g (equivalent to oven-dried weight) of pre-incubated soil was placed in a glass jar (1165 mL volume) and adjusted to a field bulk density of 1.34 g cm(.)(-3) All the glass jars were placed randomly and incubated for 15 days under aerobic condition. Results and discussion Alone application of NH4+ released more N2O (peak at 16.27 mu g N kg(-1)) than alone NO3- application. However, combined application of glucose with NO3- could emit more N2O than when combined with NH4+, and the highest N2O peak value was found in 0.5 g kg(-1)of glucose. When pectin is combined with NH4+, resulted in higher accumulated N2O emissions than other C sources, while applying straw and cellulose had negligible effects on N2O emissions but enhanced CO2 emissions under the incubation conditions. Glucose and pectin were identified as two labile C sources, significantly enhanced N2O emissions. As expected, C addition could stimulate mineral N immobilization. Conclusions Combined application of C and N enhanced N2O and CO2 emissions albeit to different extents. A higher accumulated N2O emission was found when C/N ratio was lower (12.5). The stimulating effect of glucose and pectin as labile C sources with N addition on N2O production should be considered, especially in soils with high pH, low organic C, and a strong ammonia oxidation potential. Therefore, it may have the potential to mitigate N2O emissions from the field when avoiding applying both N and C especially rich in glucose and pectin together.