| Soil salinization is one of the environmental factors that restrict agricultural production.This study has proposed a new technique to restrain soil evaporation,retain moisture and control salinization thus helping to improve the saline soils and increase sunflower yield through burying a straw layer at a depth of 40 cm combing with plastic film mulch.Deep burial of straw breaks the original balance of the soil system and will inevitably have a significant impact on the organic carbon(SOC)and total nitrogen(TN)of the soil profile.However,there is currently a lack of research on this aspect,especially the mechanism of carbon and nitrogen distribution in the soil layer near the straw barrier and the deep soil is still unclear.Therefore,this article had taken the saline-alkali land in the Hetao irrigation area as the research object,and set up different straw interlayer treatments(CK:0t·hm-2,SL6:6 t·hm-2,SL12:12 t·hm-2,SL18:18 t·hm-2).In order to reveal the influence mechanism of straw interlayer on the change of carbon and nitrogen in saline alkali soil in Hetao irrigation area,the changes of SOC,TN and their related factors(water and salt factors,microbial community structure,enzyme activity)were studied.The main progress was as follows:(1)The effects of different amounts of straw interlayer on the SOC and TN of saline-alkali soil profile were clarified.Different amounts of straw interlayer treatments were increased SOC(15.79%-23.47%),TN content(8.64%-12.59%)and soil C:N ratio insoil profile of 2015-2018,especially in 20-40 and 40-60 cm soil layers.Among them,the increase of SL12 was the most significant,and the difference between treatments decreased significantly with the increase of the burying time of the straw interlayer.At the same time,the straw barrier can reduce the surface accumulation of SOC and TN,reduce the stratification ratio,and improve the uniformity of carbon and nitrogen distribution in the soil profile.(2)The relationship between SOC,TN and soil water and salt was revealed,and it was cleared that the distribution of water and salt before sowing has a significant effect on the long-term change of SOC.According to the distribution of soil water and salt in four years.Before sowing,the soil water content of SL6,SL12 and SL18 increased by 1.68-8.61%than that of CK,and the soil salt content of SL6,SL12 and SL18 decreased by 2.85-46.96%than that of CK.After harvest,different straw interlayer treatments(SL6,SL12 and SL18)reduced the content of water and salt in 0-40 cm soil layer.The results of salt concentration in the soil solution during 2015-2018 showed that buried the straw interlayer can reduce the salt solution concentration in the 0-40 cm soil layers before sowing and after harvest.The greater the amount of straw interlayer,the stronger the effect of water retention and salt suppression.However,with the increased of the straw interlayer buried period,the effect on controlling soil water and salt was weakening.The correlation results showed that both SOC and TN were significantly positively correlated with soil water content before sowing,and significantly negatively correlated with soil salinity and salt solution concentration.And with the increase of straw buried years,the SOC content of each soil layer was mainly affected by the water and salt content before sowing.(3)The physical-biological mechanism of the distribution characteristics of SOC and TN in the soil layer near the barrier layers(35-40 and 40-45 cm)and deep layers(45-75 cm)after 6 years was revealed.Compare with CK,different straw interlayer treatments significantly increased the SOC and TN content in the particles,significantly increased the distribution ratio of POM-C and POM-N;different straw interlayer treatments significantly reduced the TN content in the mineral bound state,but the SOC content in the mineral bound state only increased significantly under SL18.Compared with CK,SL12 and SL18 significantly increased the amount of PLFA,bacteria,fungi,actinomycetes,eukaryotic microorganisms,G+and G-in the 35-40 cm,40-45 cm soil layer,and also significantly increased enzyme activity in the 35-75 cm soil.The RDA results showed that,POM-C was an important factor affecting soil microbes,and MAOM-N was an important factor affecting soil enzyme activities in the 35-40 cm and 40-45 cm soil layers.The results of VPA showed that SOC was mainly affected by the interaction between microorganisms,enzyme activity and SOC components,while TN was mainly affected by the interaction between microorganisms,enzyme activity.In conclusion,deep burial of straw layer changed the distribution of SOC and TN in soil profile,which was closely related to the contents of soil water and salt.When the amount of straw was 12t·hm-2,soil carbon and nitrogen could be significantly increased.SOC in deep layers were mainly affected by microorganisms,enzyme activities,SOC components and the three together,while TN was mainly affected by microorganisms,enzyme activities and both. |
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