翻压紫云英对稻田土壤还原物质变化特征及温室气体排放的影响

采用室内培养试验监测紫云英翻压后土壤还原物质和温室气体的动态变化,旨在为紫云英还田造成水稻僵苗及带来的环境效应提供理论依据。结果表明,翻压紫云英显著增加土壤还原性物质总量、活性还原性物质含量、Fe²⁺和Mn²⁺含量,显著降低土壤氧化还原电位(Eh)。与对照(CK)相比,翻压紫云英15000(M₁)、30000(M₂)、45000 kg·hm^-2(M₃)处理土壤还原性物质总量平均值分别增加0.34、0.80、1.16 cmol·kg^-1,土壤活性还原性物质含量平均值分别增加0.14、0.35、0.52 cmol·kg^-1,Fe²⁺含量平均值分别增加87.91、182.91、280.61 mg·kg^-1,Mn²⁺含量平均值分别增加10.12、12.77、15.73 mg·kg^-1,Eh平均值分别降低32.88、47.98、57.26 mV。还原性物质均在培养近15 d时达到高峰,M₃处理Fe²⁺含量最高超过400 mg·kg^-1,已达到水稻幼苗中毒浓度。翻压紫云英显著增加CO₂、CH₄排放,降低N₂O排放,增加了全球增温潜势(GWP)。与CK相比,M₁、M₂、M₃的CO₂排放速率平均值分别增加7.67、12.48、20.54 mg·kg^-1·d^-1,CO₂累计排放量分别增加171.63、293.42、498.45 mg·kg^-1,CH₄排放速率平均值分别增加0.04、0.09、0.21 mg·kg^-1·d^-1,CH₄累计排放量分别增加0.36、0.69、1.77 mg·kg^-1,N₂O排放速率平均值分别降低0.46、0.64、0.72 μg·kg^-1·d^-1,N₂O累计排放量分别降低10.00、13.02、14.36 μg·kg^-1,M₁、M₂、M₃的GWP平均值分别是CK的1.59、2.04、2.91倍。CO₂、N₂O排放主要集中在培养前期,CH₄排放主要集中在培养后期。还原性物质含量与CO₂、CH₄的排放呈显著正相关,与N₂O排放呈显著负相关。综上,翻压紫云英增加还原性物质含量,促使CO₂、CH₄排放,抑制N₂O排放,增加GWP。实践中翻压紫云英可增加水稻产量,探索适宜紫云英翻压量确保单位水稻产量下的GWP不增加实现增产和环境效应的双赢具有重要实践意义,但这需要通过盆栽和大田试验验证。

Effects of incorporating Chinese milk vetch on reductive material characteristics and greenhouse gas emissions in paddy soil

A 28?day laboratory incubation experiment was conducted to explore the environmental impacts of incorporating Chinese milk vetch into paddy soil. Chinese milk vetch was incorporated into soil at rates of 0 (CK), 15000, 30000, and 45000 kg?ha (M1, M2, and M3, respectively), and the dynamic changes in reducing substances and greenhouse gas emissions in paddy soil were monitored. Incorporation of Chinese milk vetch significantly increased the total soil reducing substances, active reductive material, and the concentrations of iron and manganese ions (Fe2+ and Mn2+) in paddy soil, but decreased the soil redox potential (Eh). Compared with CK, the M1, M2, M3 treatments increased total soil reducing substances by 0.34, 0.80, 1.16 cmol?kg-1, respectively; increased the active reductive material content by 0.14, 0.35, and 0.52 cmol?kg-1, respectively; increased the average Fe2+ content by 87.91, 182.91, and 280.61 mg?kg-1, respectively; increased the average Mn2+ content by 10.12, 12.77, and 15.73 mg?kg-1, respectively, and decreased the average Eh by 32.88, 47.98, and 57.26 mV, respectively. The total reducing substances content peaked after 0.5 months of incubation. The Fe2+ content in the M3 treatment increased to >400 mg?kg-1, which may result in poisoning of rice seedlings. Incorporation of Chinese milk vetch significantly increased CO2 and CH4 emissions, but decreased N2O emissions, and ultimately increased the global warming potential. Compared with CK, the M1, M2, M3 treatments increased the average CO2 emission rate by 7.67, 12.48, and 20.54 mg?kg-1?d-1, respectively; increased the average accumulative emission of CO2 by 171.63, 293.42, and 498.45 mg?kg-1, respectively; increased the average CH4 emission rate by 0.04, 0.09, and 0.21 mg?kg-1?d-1, respectively; increased the average accumulative emission of CH4 by 0.36, 0.69, and 1.77 mg?kg-1, respectively; decreased the average N2O emission rate by 0.46, 0.64, and 0.72 μg?kg-1?d-1, respectively; and decreased the average accumulative emission of N2O by 10.00, 13.02, and 14.36 μg?kg-1, respectively. The global warming potential of the M1, M2, and M3 treatment was 1.59?times, 2.04?times, and 2.93?times higher, respectively, than that of CK. The CO2 and N2O emissions were mainly concentrated in the earlier period of incubation, while CH4 emissions were concentrated in the later period of incubation. The reducing substances content was positively correlated with CO2 and CH4 emissions, but negative correlated with N2O emissions. The results showed that incorporating Chinese milk vetch significantly increased the reducing substances content, enhanced CO2 and CH4 emissions, and decreased N2O emissions. Importantly, Chinese milk vetch incorporation increased the rice yield. Therefore, there is potential value in incorporating Chinese milk vetch into soil to maintain rice yield, but it should be incorporated at appropriate rates to reduce environmental impacts. Appropriate incorporation rates should be verified through pot and field experiments.