沼液中HCO^(-)_(3)对土壤CO_(2)释放的影响

Effects of HCO^(-)_(3)in the biogas slurry on CO_(2)release from soils

【目的】揭示沼液施用过程中HCO^(-)_(3)对土壤CO_(2)释放的影响机制。【方法】分别向土壤添加沼液原液(BS)、原液去除HCO^(-)_(3)(BS⁃B)、去离子水加HCO^(-)_(3)(W+B)和去离子水(W)后,对土壤进行30 d的培养,观测土壤CO_(2)释放特征。【结果】BS处理下,土壤CO_(2)释放速率从2 h时的36.6 mg/(kg·h)快速降至30 d时的2.7 mg/(kg·h),BS⁃B处理CO_(2)释放速率从最高时的9.3 mg/(kg·h)(第1天)降至1.9 mg/(kg·h)(第30天),前者显著高于后者。30 d内,BS处理下土壤CO_(2)累计释放193.0 g/kg,BS⁃B处理下仅为97.8 g/kg。由此可见,沼液中的HCO^(-)_(3)显著促进了土壤CO_(2)的释放。相比较而言,W+B处理下土壤CO_(2)释放速率从最高时的12.0 mg/(kg·h)降至15 d时的0.6 mg/(kg·h),培养期内土壤CO_(2)累计释放54.5 g/kg;W处理下土壤CO_(2)释放速率在培养期内的变化为0.2~1.6 mg/(kg·h),CO_(2)累计释放34.4 g/kg。培养期内,BS处理下土壤CO_(2)释放量是BS⁃B与W+B两处理之和的1.6倍。HCO^(-)_(3)对土壤CO_(2)释放的贡献主要发生在上覆水层,且以HCO^(-)_(3)水解及NH+4氧化贡献的H+与HCO^(-)_(3)的相互作用为主要途径。【结论】施用沼液后,大量HCO^(-)_(3)的添加是引起土壤CO_(2)释放加快且释放量增加的主要原因之一,土壤CO_(2)释放的增加并非HCO^(-)_(3)本身与除HCO^(-)_(3)之外沼液其他组分贡献的加和,二者存在显著的协同作用。

【Objective】The biogas slurry is rich not only in NH^(+)_(4),but also in HCO^(-)_(3).This study aimed to reveal the impact of HCO^(-)_(3)on the release of CO_(2).【Mothed】when the biogas slurry was applied in farmlands,by arranging and adding four types of culture mediums,namely,the original biogas slurry,original liquid for removing HCO^(-)_(3),deionized water plus HCO^(-)_(3)and deionization water,designated as BS,BS⁃B,W+B and W treatments,respectively,to the paddy soil for a 30⁃day cultivation experiment.【Result】The soil CO_(2)release rates were observed.The results indicated that under the BS treatment,the soil CO_(2)release rates decreased rapidly from 36.6 mg/(kg·h)at 2 h to 2.7 mg/(kg·h)at 30 d,and those for the BS⁃B treatment decreased from the highest 9.3 mg/(kg·h)at 1 d to 1.9 mg/(kg·h)at 30 d.The CO_(2)release rates in the BS treatment were significantly higher than those in the BS⁃B.Within 30 d,the cumulative CO_(2)emission under the BS was 193.0 g/kg,while that in BS⁃B was only 97.8 g/kg.It was evident that the presence of HCO^(-)_(3)in the biogas slurry significantly increased the release of CO_(2)from the soil.In comparison,the CO_(2)release rate under the W+B treatment decreased from the highest value of 12.0 mg/(kg·h)to 0.6 mg/(kg·h)at 15 d,with a cumulative CO_(2)emission of 54.5 g/kg during the culture period.The CO_(2)release rate under W treatment varied from 0.2 to 1.6 mg/(kg·h)during the culture period,and the cumulative CO_(2)emission was only 34.4 g/kg.It is evident that the CO_(2)emission under the BS treatment was 1.6 times higher than that under BS⁃B and W+B treatments together.Further analysis indicated that the contribution of HCO^(-)_(3)to the CO_(2)release in the paddy soils mainly occurred in the overlying water layer,which was dominated by HCO^(-)_(3)hydrolysis and the reaction between HCO^(-)_(3)and H^(+) from NH^(+)_(4) oxidation.【Conclusion】With biogas slurry applying,the addition of a large amount of HCO^(-)_(3)was one of the main reasons for the acceleration and increase of soil CO_(2)release,which was not just a simple sum of contributions from HCO^(-)_(3)and the other components of the biogas slurry,and there was a significant synergistic effect between the two.