| Xinjiang is a typical saline-alkali soil distribution area in China,and the degree of saline-alkali soil is increasing year by year,which seriously restricts the sustainable development of agriculture.The improvement of saline-alkali soil by green manure is mainly through soil fertilization,improving soil microbial structure and environment,and reducing saline-alkali ion content,so as to achieve the effect of improving saline-alkali soil.Rape,as a new type of green manure,is rich in various nutrients,with wide adaptability,strong stress resistance,large biomass and strong adaptability to salt and alkali,which can effectively reduce the salt content in saline-alkali land.In this paper,the effects of rape green manure returning for 1 year,2 years and no returning on organic nitrogen components,nitrogen invertase activity and bacterial community structure in saline-alkali soil were studied and analyzed in the newly reclaimed moderate saline-alkali wasteland in northern Xinjiang.The main results are as follows:1.Rape green manure returning could increase the contents of total nitrogen,nitrate nitrogen and ammonium nitrogen in saline-alkali soil,and increased with the increase of returning years.R1 treatment increased by 13.39%-18.76%,20.11%-69.84% and 10.96%-18.64%,compared with R0 treatment,and R2 treatment increased by 40.25%-50.93%,30.64%-97.97% and 24.55%-29.69% compared with R0 treatment.The contents of total nitrogen,nitrate nitrogen and ammonium nitrogen in 0 ? 60 cm soil layer gradually decreased with the deepening of soil depth.2.Rape green manure returning increased the content of organic nitrogen components in saline-alkali soil,and the content of each component in R2 treatment was higher than that in R1 and R0 treatment.Under different treatments,rape green manure returning significantly increased the contents of THAN and NHN in saline-alkali soil,and R1 treatment increased by 2.81%-8.12% and 48.7%-64.25% compared with R0 treatment,and R2 treatment increased by 34.16%-43.22% and 64.6%-83.55% compared with R0 treatment.With the increase of returning years,the content of organic nitrogen components increased.Compared with R0,AAN,ASN,AN and HUN increased by 1.67%-3.34%,6.21%-14.39%,2.88%-14.83%and 3.21%-15.05%% under R1 treatment and 37.61%-40.88%,63.87%-71.74% and 3.58%-47.05% and29.88%-47.74% under R2 treatment.The increased organic nitrogen components in soil are mainly concentrated in ASN and NHN.At the same time,soil organic nitrogen components in 0?60cm soil layer under different treatments from high to low is as follows: AAN > AN > NHN > HUN > ASN.3.With the increase of returning years in 0?60cm soil layer,the activities of urease and nitrite reductase in saline-alkali soil increased by rape green manure returning.Among them,the increase was the most obvious under R2 treatment,which increased by 98.12%-137.3% and 45.94%-96.14%,respectively.There was a significant difference between R1 and R0 treatments.Under T2 treatment,protease and nitrate reductase increased significantly from 0 to 40 cm,increasing by 20.52%-63.78% and 16.87%-32.04%,respectively.With the deepening of soil depth,the activity of soil nitrogen invertase gradually decreased.4.Rape green manure returning changed the amount of OTU in saline-alkali soil,but there was no obvious difference in OTU abundance between different treatments and different soil layers.In Alpha diversity index,Ace index,Chao index and Shannon index increased in 20?40cm soil layer with the increase of returning years.Compared with R0,R1 and R2 treatments increased by 5.11% and 8.79%,4.57% and 8.62%,2.28% and 4.38% respectively,but the increase was not obvious.The Simpsom index of R2 treatment decreased significantly by 78.79% at 40 ? 60 cm,and the diversity performance was the best.The abundance of bacterial microorganisms in the 0-40 cm soil layer of R2 treatment was the highest(488and 444 OTUs unique),and the abundance of bacterial microorganisms in the 40-60 cm soil layer of R1 was the highest(356 OTUs unique).At the same time,5 dominant fungi(Chloroflexi,Acidobacteria,Actinobacteria,Proteobacteria and Gemmatimona Detes)and 3 dominant fungi(Alphaproteobacteria,Gammaproteobacteria and Actinobacteria)increased in different soil layers under the treatment of returning green manure to the field.Conclusion: Rape green manure returning increased the content of inorganic nitrogen in moderately saline-alkali soil,increased the ratio of NHN and ASN in organic nitrogen,and decreased the ratio of HUN and AN.Rape green manure returning can improve the availability of nitrogen in saline-alkali soil,promote the accumulation and transformation of nitrogen in soil,and improve the nitrogen supply capacity of soil by improving the activity of soil nitrogen invertase and the richness and diversity of soil bacteria. |
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