Influence of Acetylene Concentration on N₂O and N₂ Emissions from an Intensive Vegetable Soil under Anoxic and Oxic Conditions

Acetylene (C₂H₂) is often employed to assess soil total denitrification (N₂O + N₂) due to its ease of implementation. However, this technique underestimates soil denitrification in soils with low nutrient contents, particularly those supporting grain yields. To our knowledge, there are limited studies that have specifically investigated the impact of C₂H₂ on nutrient-rich vegetable soils, especially concerning the emissions of N₂ and N₂O and the nitrogenous gas product ratio (i.e., N₂O/(N₂O + N₂)). In this study, we conducted both anoxic and oxic incubations at various C₂H₂ concentrations (0%, 0.01%, and 10%, v/v) and utilized a robotized sampling and analysis system to quantify soil N₂, N₂O, and CO₂ emissions. Our findings revealed that the cumulative N₂O production in soil treated with 10%C₂H₂ was significantly lower than that in soil treated with 0.01%C₂H₂ and soil without C₂H₂. Contrarily, high concentrations of C₂H₂ (10%, v/v) led to increased N₂ production. Similar trends were observed under oxic conditions, where 10%C₂H₂ concentration did not enhance N₂O production but markedly increased N₂ and CO₂ emissions. Moreover, the N₂O/(N₂O + N₂) product ratio was notably higher in soils treated with 0%C₂H₂ compared to the 10%C₂H₂ treatment under anoxic conditions. These findings indicate that high concentrations of acetylene could facilitate the reduction of N₂O to N₂ and lead to underestimated soil total denitrification in vegetable soil, regardless of anoxic or oxic conditions. This discovery underscores the drawbacks when employing high concentrations of acetylene to evaluate actual total denitrification in intensive greenhouse vegetable soils, highlighting the necessity for further investigation into alternative methodologies.