Effects Of Ameliorant Application On Greenhouse Gas Emissions From Camellia Oleifera Plantation Soil Under Nitrogen Fertilization

Camellia oleifera Abel.is one of the world's four main woody edible oil crops with a wide cultivation area in subtropical China.In this region,hydrothermal condition was excellent,but the soil fertility was poor.Although intensive management with fertilization has been used to increase the yield of C.oleifera,input of intensive nitrogen(N)fertilizer increased the risk of soil acidification and soil greenhouse gas(GHG)emissions,constraining sustainable development of C.oleifera industry.Therefore,choosing appropriate soil ameliorants for mitigating soil acidification and GHG emissions and increasing yield is beneficial to the edible oil and ecological environment security of China.Recently,application of biochar,nitrification inhibitors,or urease inhibitors provided a new way to solve above problems.In this study,effects of ameliorant application on greenhouse gas emissions from Camellia oleifera plantation soil under nitrogen fertilizationwere conducted in fields and labs.Two short-term in situ studies showed that(1)both C.oleifera fruit shell-derived biochar and dicyandiamide(DCD,a nitrification inhibitor)application reduced soil nitrous oxide(N₂O)emission rates under ammonium nitrate(NH₄NO₃)fertilization.NH₄NO₃ fertilization increased the yield of C.oleifera seed,but a three-fold increase of cumulative soil N₂O emissions was also observed following NH₄NO₃fertilization.No significant effects were observed by biochar application on the yield of C.oleifera seed under NH₄NO₃ fertilization,but DCD application decreased the yield of C.oleifera seed under NH₄NO₃ fertilization.(2)C.oleifera fruit shell-derived biochar application reduced the increase of average soil N₂O emission rates induced by organic manure(quail manure)fertilization.The main results of incubation studies were as follows:(1)Biochar(control,spent mushroom substrate(MS)-derived biochar and C.oleifera fruit shell(FS)-derived biochar),water content(60%,120%,240%or 360%water holding capacity(WHC))and organic manure(control or chicken manure)interactively affected cumulative soil methane(CH₄)and N₂O emissions and the copy number of Aamo A,Bamo A,nir K,nir S and nos Z genes.Organic manure fertilization increased the risk of CH₄ and N₂O emissions.Flooding treatment(240%and 360%WHC)increased cumulative soil CH₄emissions under MS biochar application and this effect was amplified by organic manure fertilization.Both FS and MS biochar application significantly increased the copy number of nir K genes under 60%WHC and organic manure fertilization,in turn,the copy number of nir S genes was decreased.MS biochar application increased the copy number of nos Z genes under 120%WHC and organic manure fertilization.(2)Combined application of C.oleifera fruit shell-derived biochar and DCD further reduced average soil net nitrification rates under urea or NH₄NO₃ fertilization(for urea treatment,decreased from 1.1 to 0.3 mg kg^-1 day^-1).Biochar application increased average soil N₂O emission rates(for urea treatment,increased from 0.03 to 0.08 ng N₂O g^-1 h^-1)and their temperature sensitivity.DCD application reduced average soil N₂O emission rates with greater reductions under urea fertilization.(3)Butylthiophosphotriamine(NBPT,a urease inhibitor)application reduced cumulative soil N₂O emissions under urea fertilization,but C.oleifera fruit shell-derived biochar application increased cumulative soil N₂O emissions under urea fertilization.Cumulative soil N₂O emissions after urea fertilization increased but then decreased with the addition rates of NBPT(0%,0.08%,0.16%,0.24%,0.32%)under different the addition rates of biochar(0,2.5%or 5%).Positive correlation was observed between soil N₂O emission rates and soil net nitrification rates.Soil N₂O emission rates and soil net nitrification rates showed a same dynamics with an increase at an earlier phase and a decrease at a later phase.(4)Feedstock particle size(C.oleifera fruit shell with three particle size fractions 0.5-2,2-5,and 5-10 mm)and pyrolysis temperature(300,450,and 600°C)interactively affected soil N₂O and carbon dioxide(CO₂)emission rates.Dissolved organic carbon in C.oleifera fruit shell-derived biochar increased with particle size when pyrolyzed at 300°C,but decreased with pyrolysis temperature.Compared with 300°C pyrolysis temperature treatment,lower soil N₂O emission rates were observed in 450 and 600°C pyrolysis temperature treatments under NH₄NO₃ fertilization.The lowest soil N₂O and CO₂ emission rates in 0.5-2 mm shell-derived biochar compared with 2-5 mm and 5-10 mm shell-derived biochar when pyrolyzed at 300°C.Additionally,the lowest net nitrification rates in 0.5-2 mm shell-derived biochar compared with 2-5 mm and 5-10 mm shell-derived biochar when pyrolyzed at 600°C.In conclusion:intensive managed C.oleifera plantationsis showed a high potential in mitigation of soil GHG emissions.In order to sustainable development of C.oleifera plantationsis,the types of N fertilizers should be considered when choosing soil ameliorants.Both feedstock type and feedstock particle size of biochar and soil water condition were important factors in soil ameliorant.Although biochar application can improve soil p H,combined application of biochar and nitrification inhibitors was suggested in mitigation of soil GHG emissions under N fertilization.Urease inhibitors rather than biochar were suggested in mitigation of soil GHG emission under urea fertilization.