Gaseous losses of fertilizer nitrogen from a citrus orchard in the red soil hilly region of Southeast China

The gaseous losses of fertilizer nitrogen (N) applied to agroecosystems are a major contributor to a host of environmental problems, inefficient production systems, and decreased N-use efficiency. These losses lead to the wastage of resources, increasing the greenhouse effect and harming human health. The red soil hilly region of Southeast China houses the biggest orchard area of the world, and nitrogen fertilizers are usually heavily applied to the orchard systems in China. Therefore, this study aimed to measure the gaseous losses of the fertilizer N by ammonia (NH₃) volatilization and denitrification losses using the venting method and acetylene inhibition method respectively, and to assess the potential environmental risk of NH₃ and nitrous oxide (N₂O) emission from this orchard system based on the recent orchard management practices. An experiment was conducted in an Ougan citrus (Citrus reticulata Blanco ‘Suavissima’) orchard in the red soil hilly region of Southeast China. Three fertilization treatments, including the control (no N fertilizer, CK), poultry manure (at a rate of 6.3 t/ha, OM), and conventional fertilization (OM 6.3 t/ha + chemical fertilizer 393 kg N/ha, CF), were used. In all treatments, the fertilizers were incorporated into the soil after application. The test results, which were continuously determined within one year, indicated that the NH₃ volatilization losses accounted for 4.5% of the OM nitrogen (OM-N) and 2.9% of the CF nitrogen (CF-N), whereas the denitrification N losses accounted for 2.1% of the OM-N and 2.9% of the CF-N. Overall, the total gaseous N losses (including NH₃ volatilization losses and denitrification N losses) were 5.8% in the CF treatment. A relatively higher N₂O flux, accounting for 1.8% of the CF-N, emitted from the CF treatment.