Extremely high N2O but unexpectedly low NO emissions from a highly organic and chemical fertilized peach orchard system in China

In China, the rapid conversion of traditional rice-wheat rotation to orchard-induced management practices has resulted in changes in soil N2O and NO emissions. However, quantification of emissions from orchard fields characterized by a high rate of organic and chemical N fertilization application has not yet been widely carried out. In this study, we measured soil N2O and NO emissions from a typical peach orchard in the Taihu region over a 2-year period using a combination of static chamber and gas chromatography techniques. Four treatments were examined: organic manure alone (OM), chemical fertilizers alone (CF), organic manure plus chemical fertilizers (OF + CF), and no fertilizers as a control (CK). No significant effects of organic amendments × chemical fertilizer application on soil N2O and NO emissions were observed. The mean annual N2O emission over the 2-year period was 3.2 kg N ha−1 under CK treatment, and increased to 9.3, 10.3, and 20.1 kg N ha−1 under OF, CF and OF + CF treatment, respectively. In contrast, cumulative NO emissions were relatively low, ranging from 0.14 to 1.99 kg N ha−1 yr−1. The NO emissions were enhanced by approximately eight fold following mineral fertilization application either alone or in combination with organic manure, and to a lesser extent (45%, nonsignificant) by organic manure application alone. Overall, NO accounted for approximately 14.5 and only 2.9% of the total (NO + N2O)-N emissions under CF and OF treatment, respectively. Over the 2-year observation period, the N2O emission factor averaged 1.69%, 1.32% and 1.86% and the NO emission factor averaged 0.03%, 0.27% and 0.17% under OF, CF and OF + CF treatment, respectively. Overall, our results suggest that fertilized peach orchard soil in the Taihu region is an important source of N2O emissions.