| The West foot of Daxing’an Mountains is the main distribution area of black land in Northeast China and also the main grain producing area in Inner Mongolia.Because of continuous cultivation,farmland can’t be recuperated and cultivated,and soil quality is decreasing year by year,which is manifested in thin black soil layer,decrease of soil organic matter,decrease of water storage and water conservation capacity,etc.It is great significance to carry out the research on the rotation system of fallow farming in black land,which is great significance to protect and improve the farmland land power,promote the sustainable use of farmland and stable grain production.The study was conducted on the influence of fallow on the physical properties,enzyme activity,microbial biomass,carbon and nitrogen,bacteria and fungi community structure of farmland under the condition of wheat rape rotation by field experiment and laboratory test analysis.The results showed that during the rest period(fallow farmland)and after the rest of the cultivation,the soil was abandoned the change law of physical and microbial characteristics of black soil in(after fallow)in,the variation characteristics of crop yield,economic benefit and land use efficiency after fallow are analyzed.The biological mechanism and the production effect mechanism of stable yield and efficiency increase of the black soil fertility are clarified under rotation conditions.It provides a theory for establishing a reasonable farming system at the West foot of Daxing’an Mountains basis.The results are as follows1.Fallow improved the pore structure of soil and was beneficial to the water accumulation in the following fieldFallow combined with straw ploughing reduced soil bulk density,and made the soil bulk density of 0-40 cm soil layer in the later stubble field significantly lower than that in the conventional rotation field.Fallow increased soil porosity.Fallow after wheat increased soil porosity more than fallow after rape,and increased soil porosity more in the year with more precipitation.Because of the decrease of soil bulk density and the increase of soil porosity,the soil water storage of fallow field was increased.Compared with cultivated crop fields,fallow increased soil water content by 23.4～65.4 mm during fallow period,and the increase of water storage in 2016 with less precipitation was higher.There was no significant difference in soil water storage between fallow field and conventional rotation field before sowing,but it laid a good foundation for soil water accumulation in the following field.2.The enzyme activity of soil in the field of fallow and after fallow was improved,and the effect after the rest was obviousThe activities of catalase,sucrase,urease and phosphatase in 0-60 cm soil layer of fallow field were increased by 12.88%～133.02%compared with conventional rotation field.The activities of catalase,sucrase and urease in 0-40 cm soil layer were increased by 0.63%～17.88%,3.44%～79.45%and 2.13%～48.98%.In terms of time,the flowering stage was the high value stage of soil enzyme activity,and the soil enzyme activity of fallow field was significantly higher than that of conventional rotation field.Fallow has a strong promoting effect on soil enzyme activity,and the effect after fallow is obvious.3.Fallow increased soil microbial biomass,and the contribution rate of microbial biomass and enzyme activity to explain soil fertility changes was higherIn the vertical space of soil layer,the microbial biomass carbon content of 0-60 cm soil layer can be increased by the rest of wheat stubble,the microbial carbon content of 0-40 cm soil layer is increased in the rest of rape stubble,and 0-60 for wheat and rape stubble.In terms of time,the content of microbial biomass C and N in flowering stage was the highest,and the content of microbial biomass C and N in fallow stubble field was 11.02%～54.51%and 12.77%～36.06%higher than that in conventional rotation field,respectively.According to the sequence of the rest,the stubble and the rotation,the correlation between microbial biomass and enzyme activity and water storage was negative and positive,from not significant to significant or extremely significant.Soil water storage is not the main factor limiting the soil quality of the rest and after fallow fields.The main indexes of soil quality in three farmland are microbial biomass carbon,microbial biomass nitrogen,catalase,urease and phosphatase activity.The comprehensive analysis shows that the quality of the soil in the rest field is the highest,followed by the stubble field after the rest,and the lowest is the rotation field,and the effect after the rest is obvious.4.The rest of the cultivation improved the community structure of bacteria and fungi.and improved the abundance of beneficial microorganismsCompared with conventional rotation field,the number of soil bacteria and fungi(OTU)and B/F were increased,and the soil changed to high fertility bacterial soil.The structure of bacteria and fungi in the gate level was not changed obviously in the rest tillage,but RB41 and Candidatus were increased at the level of bacterial genera.The relative abundance of beneficial bacteria,such as Solibacter,Gemmatimonas and massilia,increased the relative abundance of probiotics such as Microdomium and Funeliformis at the level of fungi.The abundance of Sphingomonas.Gailla.Rubrobacler.Microlunatus,Blastococcus,Bradyrizbium and other bacterial genera in the soil after fallow was negatively correlated with the bulk density,but the fallow had no significant effect on the diversity of bacteria and fungi community.5.The effect of fallow on the yield and efficiency of the crops after stubble is obvious,and the land use efficiency is restored quicklyThe yield components of the later crop were improved by rest tillage,and the length of wheat ear,the number of grains per ear,the effective number of effective pod per plant and the number of per corner grain of rape were increased.The yield of wheat in the first crop after fallow was 32.46%to 43.23%higher than that of conventional rotation,and 40.39%to 69.66%after the rest.According to the analysis of rotation time series effect,although the effect of no crop planting during the rest period reduces the land utilization rate,the effect of crop yield increase can reach more than 5 years under the effect of the effect of fallow cultivation.Taking 5-6 years as a rotation cycle,the land equivalent ratio can be equal to that of conventional rotation.At the same time,the yield of each crop and the yield equivalent ratio of rotation were increased by the rest of the cropland.The economic benefit of crop production can be increased by more than 3 years by rest of farming.The rotation benefit equivalent can be basically equivalent to that of conventional rotation,taking 3-5 years as a rotation cycle.In conclusion,this study revealed the law of the effects of fallow on soil physical properties,enzyme activities,microbial biomass and microbial community characteristics under the conventional rotation mode,clarified the key indicators indicating the improvement of black soil fertility,clarified the mechanism of stable yield and efficiency of the stubble field after fallow,and clarified the biological mechanism of fallow on improving soil fertility.It provides a theoretical basis for establishing a reasonable farming system in the west of Daxing’an Mountains in Inner Mongolia. |
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