Effect Of Humic Acid Fertilization On Soil CO₂ Flux And Its Relative Factors In Wheat-maize Rotation System

Humic acid fertilizer plays an active role in increaseing crop growth and yield,improving soil physical and chemical properties,regulating soil carbon balance and so on,but the sources and active methods of humic acid are essential for the efficiency of humic acid fertilizer.Three application levels of humic acid fertilizers derived from weathered coal with oxydic and alkali activation,in cluding Blank nitrogen?N?free fertilization,CK:conventional N fertilization,OHA1:conventional N fertilization+500kg·hm^-2 humic acid fertilizer derived from oxydic activation,OHA2:conventional N fertilization+1000kg·hm^-2 humic acid fertilizer derived from oxydic activation,OHA3:conventional N fertilization+1500kg·hm^-2humic acid fertilizer derived from oxydic activation,AHA1:conventional N fertilization+500kg·hm^-2 humic acid fertilizer derived from alkali activation,AHA2:conventional N fertilization+1000kg·hm^-2 humic acid fertilizer derived from alkali activation,AHA3:conventional N fertilization+1500kg·hm^-2 humic acid fertilizer derived from alkali activation,were carried out in wheat-maize rotation ecosystem with cinnamon soil in Tai'an,Shandong Province during 2018-2019.The effects of eight treatment on soil CO₂ flux,basic physical and chemical properties,biological characteristics,soil organic carbon and some of its active components were investgated to to elucidate the response mechanism of soil CO₂flux to the type and amount of humic acid fertilizer in wheat-maize rotation system.The purpose of this study wasThe main results are as follows:?1?Compared with CK,the cumulative flux of CO₂ in humic acid treatment increased significantly in 2018 and 2019,among which CO₂ cumulative flux of AHA2 was the highest in 2018 wheat season,over 26.68%higher than blank,that of OHA3 was the highest in 2019wheat season,and AHA2 was the second,over 18.52%and 15.83%higher than blank.The cumulative CO₂ fluxes in maize season were the highest observed in AHA2,which were over14.09%and 9.69%higher than blank in 2018 and 2019 respectively.According to the stepwise regression analysis,the content of soil available potassium in wheat season was the direct factor of soil CO₂ accumulation flux,while the aboveground biomass in maize season was the direct factor of soil CO₂ accumulation flux.?2?Compared with CK,humic acid application reduced soil bulk density.In 2019,soil bulk density of OHA3 and AHA3 in wheat season decreased by 5.54%and 5.32%compared with CK,while that of AHA2 and AHA3 in maize season decreased 8.56%and 8.33%compared with CK.In the maize season of 2019,OHA2 significantly increased the average weight diameter of soil aggregates compared with CK.Compared with CK,some physical and chemical indexes?pH,EC,total nitrogen,available nutrients?in soil treated with humic acid fertilizer were improved to some extent.In 2018,the total nitrogen content of AHA3 was the highest in wheat season and maize season,and in 2019,the total nitrogen content of AHA2 was the highest in wheat season and maize season,with a significant increase of 22.42%and 22.39%compared with CK.Application of humic acid fertilizer effectively alleviated the rapid decline trend of soil available nutrients in wheat jointing stage and maize bellmouth stage.At the jointing stage of wheat and the bellmouth stage of maize in two years,the content of nitrate nitrogen,ammonium nitrogen,available potassium and available phosphorus in all treatment with humic acid fertilizer was significantly higher than CK.?3?Application of humic acid fertilizer increased soil organic carbon and its active components,soil microbial biomass carbon and nitrogen content.In 2019,the content of organic carbon in humic acid fertilizer treatment of wheat and maize was significantly higher than CK,and the increase range was 16.59%²6.33%,10.88%²2.87%respectively,and the content of AHA2 was the highest.In the wheat season,OHA3 and AHA1,in the maize season,OHA3,AHA1,AHA2 and AHA3,the soil dissolved organic carbon content was significantly higher than CK in 2019.In 2019,the content of soil easily oxidized organic carbon in OHA2and AHA2 increased by 37.19%and 58.43%compared with CK.In 2019,soil microbial biomass carbon content of OHA2,OHA3 and AHA3 increased significantly compared with CK.?4?The application of humic acid fertilizer significantly increased the aboveground biomass and yield of wheat and maize.In 2018,except for OHA2 and AHA1,wheat yield of other humic acid fertilizer treatment increased significantly compared with CK;maize yield of other humic acid fertilizer treatment increased significantly compared with CK except for AHA1.In 2019,maize yield of treated with humic acid fertilizer increased significantly compared with CK.For two consecutive years,the biomass and yield of wheat season and maize season were the highest in AHA2.In 2018,the biomass of wheat season and maize season were 14.15t·hm^-2 and 18.79t·hm^-2,respectively,which were 14.07t·hm^-2 and17.96t·hm^-2 in 2019.The yield of wheat in 2018 and 2019 was 7.44t·hm^-2 and 7.20t·hm^-2respectively,while that of maize in 2018 and 2019 was 9.78t·hm^-2 and 9.28t·hm^-2respectively.In conclusion,the application of humic acid fertilizer can effectively improve the soil physical and chemical properties under the wheat-maize rotation system in the cinnamon soil and enhance the soil fertility.In the perspective of ecological agriculture,middle dosage alkali activated humic acid fertilizer is the best fertilizer model based on the economic benefits such as comprehensive yield.The experimental results provide theoretical guidance and data support for the application and promotion of humic acid fertilizer,as well as the improvement of land productivity and the protection of ecological environment in the cinnamon area.