氮肥对不同无机碳含量土壤二氧化碳释放的影响

施用氮肥会导致土壤pH值降低,其对不同无机碳含量的土壤二氧化碳(CO₂)释放的影响如何,尚不清楚.采用室内密闭培养试验研究了氮肥及其配施硝化抑制剂(DCD)对不同无机碳含量土壤pH、矿质态氮和CO₂释放的影响.结果表明:与不施氮肥相比,施用氮肥不同程度地降低了水稻土、砂姜黑土、塿土3类供试土壤的pH,提高了土壤碳累积释放量,49 d培养结束时,土壤碳累积释放量分别提高了39.4%、23.4%和71.8%;氮肥配施DCD后显著抑制了土壤硝化作用的进行,至培养结束时,3类供试土壤pH值均显著高于仅施氮肥处理,水稻土、砂姜黑土CO₂平均释放量与仅施氮肥相比无显著性差异,塿土CO₂平均释放量比纯施氮肥平均降低了12.5%.土壤无机碳能有效缓冲由氮肥施入而导致的土壤酸化,氮肥施入后石灰性土壤CO₂释放不仅来源于土壤有机碳的矿化,可能还有一部分来源于无机碳的溶解释放.我国不同地区间土壤无机碳含量各有差异,长期大量氮肥投入下土壤酸化和无机碳库消耗问题应引起足够的重视.

Effects of nitrogen fertilizer application on carbon dioxide emissions from soils with different inorganic carbon contents.

The application of nitrogen (N) fertilizer results in decreases of soil pH, but its effects on CO₂ emission from soils with different inorganic carbon contents remain unclear. An closed-jar incubation experiment was conducted to examine the effects of N fertilizer and nitrification inhibitor (DCD) on soil pH and CO₂ emissions from three soil types with different contents of soil inorganic carbon (SIC), including paddy soil (PS), lime concretion black soil (CS), and eum-orthic anthrosols (AS). There were three treatments for each soil type, including control (N₀), 0.2 g·kg^-1 N fertilizer (N_0.2), and its combination with DCD (N_0.2+DCD). Soil pH, contents of mineral N (NH₄⁺, NO₃^-), and CO₂ emissions were measured. The results showed that N fertilizer addition significantly reduced soil pH and increased soil CO₂ cumulative emissions in each type of soil. Compared to control, the CO₂ cumulative emissions after 49 days incubation from the three soil types were enhanced by 39.4%, 23.4%, and 71.8% for PS, CS, AS soils, respectively. The soil pH of N_0.2+DCD for three soil types were significantly higher than N_0.2 after 49 days incubation, indicating that DCD application inhibited soil nitrification process. There were no significant differences in the mean CO₂ cumulative emissions of PS and CS soils between N_0.2 and N_0.2+DCD treatments; however, N_0.2+DCD treatment significantly reduced cumulative CO₂ emissions from AS soil by 12.5%. Soil inorganic carbon can effectively buffer soil acidification caused by N fertilizer addition. The CO₂ emission in calcareous soil following N addition is not only derived from the mineralization of soil organic carbon, but also from the dissolution of inorganic carbon. Given the large differences in soil inorganic carbon content in different regions of China, the problem of soil acidification and soil inorganic carbon pool consumption caused by long-term large amount of N fertilizer inputs deserve more attention.