The Effects Of Fertilization And Cadmium Addition On Greenhouse Gases Emissions From Soils Planted With Forage Soybean

Greenhouse gases(GHGs;carbon dioxide,CO2,nitrous oxide,N2O and methane CH4)emissions from soils have attracted considerable researcher's attention in recent years.Both forage soybean growth and GHG emissions from soils are generally affected by fertilizer application and cadmium(Cd)contamination.However,the research of GHG emissions on different fertilizations from Cd contaminated soil planted with forage soybean is severely lacking.Therefore,in order to choose appropriate fertilization of forage soybean,a greenhouse lysimeter experiment was conducted to explore the effects of fertilizer application(control(CK),chemical fertilizer(N),organic manure(M),chemical fertilizer in combination with organic manure(NM))on GHG emissions from different Cd-contaminated soils(0,10 and 20 mg Cd kg-1)with equal nitrogen addition.The main results are as follows:1)The maximum fluxes of N2O normally occurred within 3 days after chemical fertilizer input.The orders of N2O concentrations along soil profile were 50 cm>30 cm>10 cm at all treatments.Cumulative N2O emissions from soils were significantly affected by fertilization.The highest cumulative N2O emissions were measured in the NM treatments at all Cd levels,except for the N treatment that showed the highest value at 20 mg Cd kg-1 treatments.Additionally,cumulative N2O emissions of M treatments were lower than those of other fertilizer treatments at all Cd levels.2)CO2 concentrations significantly increased with increasing soil depth at all treatments,and the orders were 50 cm>30 cm>10 cm.Fertilization had significant effects on cumulative CO2 emissions from soils at all Cd levels.The highest cumulative CO2 emissions were measured in the M treatments at all Cd levels,following by NM and N treatments.3)CH4 concentrations didn't significantly varied with increasing soil depth at all treatments.Fertilization had no significant effect on cumulative CH4 emissions from soils planted with forage soybean at all Cd levels.In addition,the CH4 consumptions were observed in N,M and NM treatments at all Cd levels,while the cumulative CH4 emissions showed no significant difference among the fertilizer treatments at all Cd levels.4)Compared with N treatments,the soil nitrate nitrogen and total dissolve nitrogen content were significantly decreased by M application at all Cd levels,which might be one of the reasons for the lower cumulative N2O emissions from organic fertilizer treatments.Meanwhile,M application significantly promoted forage soybean growth,reduced the Cd uptake throughout all Cd addition treatments,and might absorb more nitrogen element from soils than other fertilizer treatments with equal nitrogen addition at same Cd level,which might be another reason for the lower cumulative N2O emissions from organic fertilizer treatments.In addition,the soil nitrate nitrogen and total dissolve nitrogen content were increased by NM application compared with M treatments at all Cd levels.And the microbial biomass carbon and nitrogen content at layer(0-20 cm)were improved by NM application in comparison to N treatments.The change in soil microbial community structure might be a plausible explanation of the higher cumulative N2O emissions from NM treatments.These results indicated that organic fertilizer application in soil planted with forage soybean not only increased shoot biomass with equal nitrogen addition,but also decreased the cumulative N2O emissions from soils and reduced the Cd content and concentration in plants.Therefore,organic fertilizer application would be a more suitable practice to improve forage soybean biomass and mitigate N2O emissions from Cd-contaminated soil.