Soil Quality Change In Alfalfa Different Stand Age And Different Rotation In Jianghuai Area

Alfalfa?Medicago sativa L.?is high quality forage widely planted in the world.It has a special intraspecific allelopathy-autotoxicity.The growth of alfalfa for many years will lead to the accumulation of soil autotoxic substances,leading to the deterioration of soil environment,decreasing yield and quality of alfalfa;even affect the growth of subsequent plants.With the continuous development of dairy industry in China,the demand for high-quality forage is increasing.The area and scope of alfalfa planting in China are increasing,and the trend of industrialization and scale is gradually formed.At the same time,the problems of soil-borne diseases,self-poisoning effects and continuous cropping are becoming more and more serious.However,for alfalfa production in the Jianghuai area,there is a lack of relevant experience,and the environment of high temperature and humidity is more likely to cause diseases,pests and continuous cropping obstacles,which seriously restricts and affects alfalfa production in the region.In this study,the soil physicochemical and biological properties of alfalfa continuous cropping,different rotation patterns and different cultivars of photosensitive Sorghum-sudangrass hybrid were studied,in order to study the effects of different rotation crops on soil quality,soil fertility and alfalfa yield in Jianghuai area.Through the above research,the results were as follows:?1?It has been demonstrated that long-term continuous cropping will result in a significant decline on pasture yield,the annual dry matter yield was 18.63±0.30 t·hectare^-1.The pH value of the root soil of 3 and 5 years old alfalfa was significantly lower than that of 0 year and 1 year old alfalfa?P<0.05?.The total nitrogen content of the root soil of 3 years old alfalfa was significantly higher than that of other ages.The available phosphorus content of the three soil layers increased with age?P<0.05?.The soil organic matter in three soil layers was significantly higher than that of alfalfa in other ages?P<0.05?;the content of soil available potassium in three soil layers decreased significantly with the increase of age?P<0.05?,and the soil chemical elements had the effect of epimerization;the order of soil bulk density in different growth ages of alfalfa was 5 yr>3 yr>0yr>1 yr,and the soil bulk density increased with the increase of soil layers.?2?In different soil layers,with the deepening of soil layer,the activity of soil sucrase gradually decreased,and the sucrase activity in the root soil of 0 yr was significantly lower than that in the root soil of alfalfa?P>0.05?;in each soil layer,the sequence of soil peroxidase was 3 yr>0yr>5yr>1 yr?P<0.05?;The soil alkaline phosphatase reached the maximum at the age of 3yr,and then decreased at the age of 5yr.The soil urease activity of Alfalfa at the age of 3yr was significantly higher than that of alfalfa at other ages?P<0.05?.Pearson correlation coefficient of alfalfa age with alfalfa yield and soil physical and chemical properties showed that alfalfa age was positively correlated with available P,negatively correlated with available K,and alfalfa annual yield with soil organic matter.Alkaline phosphatase and urease showed significant positive correlation?P<0.01?,and total nitrogen,available potassium and catalase showed significant positive correlation?P<0.05?.?3?We investigated the soil microbial community composition across alfalfa?Medicago sativa L.?fields at different stand ages,by using Illumina MiSeq analysis of bacterial 16S and fungal 18S ribosomal RNA?rRNA?,we found that bacterial richness and diversity notably decreased in 3 yr and 5 yr fields while fungal richness and diversity increased in 3 yr and 5 yr,the bacterial OTUs was 1 yr>0yr>3yr>5yr and fungal OTUs was 1 yr>0yr>5yr>3 yr.The relative abundance of bacterial and fungal in alfalfa soils had different variation with increasing of the stand age,and the further correlation analysis revealed that several bacterial and fungal relative abundances were closely associated with the alfalfa yield change.Our results also showed that pH,AK,AP were the main influencing factors of soil bacterial community diversity,pH,OM,TN were the influencing factors.Overall,it is concluded that the increase of alfalfa stand ages significantly altered soil microbial community structures;the organic matter,urease activity,soil fungal diversity and relative abundances of Candidate division-WS6,Spirochaetae,Basidiomycota,Chytridiomycota and unclassified_dEukaryota were associated with alfalfa yield.?4?We studied the biological characteristics,nutrient composition changes and yield from four Sorghum-sudangrass hybrid cultivars:Big Kahuna?DK?,BJ0603?GDC?,Pa Kahuna?PK?and Monster?HN?.The results showed that except Monster?HN?,the other three cultivars could not complete reproductive growth in Jianghuai area;Grey correlation analysis showed that plant height and leaf weight were the most closely related traits determining fresh grass yield;The fresh grass yield of BJ0603?GDC?was significantly higher than other cultivars,the standard grass yield and dry matter yield of Pa Kahuna?PK?and BJ0603 was significantly higher than that of Monster?HN?and Big Kahuna?DK?;The standardized grass yield and the dry matter production under one cut were higher than those under two cuts,while the fresh grass production under two cuts was significantly higher.The acid detergent fiber?ADF?and neutral detergent fiber?NDF?gradually increased with the growth period;the crude protein?CP?content reached the highest value at the booting stage,crude ash content?ASH?gradually decreased with the growth period increasing.The contents of acid detergent fiber?ADF?,neutral detergent fiber?NDF?,crude protein?CP?and crude ash?ASH?in stems were different among cultivars.In summary,in the spring planting photosensitive Sorghum×Sudangrass in Jianghuai area,all cultivars performed well and it was fit for 1 cut.The cutting is the best at booting stage in Monster?HN?and BJ0603?GDC?while Pa Kahuna?PK?and Big Kahuna?DK?should be little earlier.?5?To investigate the effects of different cultivars of photosensitive Sorghum-sudangrass hybrid on soil microecological environment in Jianghuai area,four Sorghum Sudangrass hybrid cultivars were selected in this study:Monster?HN?,Big Kahuna?DK?,BJ0603?GDC?and Pa Kahuna?PK?.Traditional methods was used to determine the physical and chemical properties of soil in different soil layers,and enzyme activities were determined by kits in rhizosphere soil,the diversity of bacterial community in rhizosphere soil was analyzed by Illumina MiSeq analysis.Results showed that the soil physical and chemical properties were significantly different?P<0.05?in soil of four cultivars;The Illumina Miseq analysis indicated that bacterial diversities were different in soil of different cultivars,The soil bacterial diversities of PK was higher than that of the other three cultivars;The redundancy analyses?RDA?analysis indicated that the soil total nitrogen?TN?and soil organic matter?OM?were the most important factors to characterized the soil bacterial community composition and the soil pH?pH?and soil organic matter?OM?were the most important factors to characterized the soil fungal community composition.In summary,the cultivars of HN,PK,DK and GDC in Jiang-huai area showed cultivar differences in soil nutrient,bulk density,enzyme activity and bacterial community structure diversity,so different planting management schemes could be formulated according to the characteristics of different cultivars.?6?To reveal effects of different crop rotations on alfalfa yield and soil quality in Jiang-huai area,four years of continuous monoculture alfalfa then replanted one year as the control?CK?was compared to the crop rotation:T₁?3 years of alfalfa-maize-alfalfa?and T₂(3 years of alfalfa-sorghum-alfalfa.Traditional methods was used to determine the alfalfa yield and physical and chemical properties of soil in different soil layers,enzyme activities were determined by kits in rhizosphere soil,and the diversity of bacterial community in rhizosphere soil was analyzed by Illumina MiSeq analysis.The results showed that incorporation of maize and sorghum into the rotation significantly improved the alfalfa yield.Specifically,alfalfa yield was 1.27 and 1.13 times higher than that in treatment of continuous alfalfa?CK?.Sorghum rotation?T₂?significantly increased soil pH and organic matter?OM??P<0.05?,total nitrogen content in rotation maize?T₁?significantly increased?P<0.05?,and available potassium content in soil significantly increased in treatments of rotation maize and sorghum?P<0.05?.Soil bulk density was reduced,and treatment of sorghum rotation was more significant.Compared with alfalfa continuous cropping,Catalase and Urease activities in rotations of maize and sorghum soil were significantly higher than those in alfalfa continuous cropping soil?P<0.05?.The Illumina Miseq analysis indicated that the diversity of soil bacterial community showed that treated with T₁ and T₂ were significantly higher than CK,OTU was 1.25 and 1.39 times and fungal community showed that treated with T₁ and T₂ were significantly higher than CK,OTU was 1.20 and 1.36 times higher than that in treatment of continuous alfalfa.Shannon,Chao,and Sobs diversity indices in treatment of T₂ were significantly higher than CK?P<0.05?.The relative abundance of Protecbacteria and Firmicutes in continuous cropping soil was significantly higher than that in rotation soil,while the relative abundance of Chloroflexi?Planctomycetes and Glomeromycota in rotation soil were significantly higher than that in continuous cropping soil.It was concluded that rotation improved soil fertility and soil enzyme activities,stabilized bacterial and fungal community structure and thus increased the alfalfa yield.Generally,stand age affects alfalfa yield and soil quality,alfalfa yield is the highest at the age of 3 in Jianghuai area,and alfalfa soil quality decreases with the increasing of alfalfa age.Establishing rotation mechanism is conducive to improving alfalfa yield and soil quality.After alfalfa stubble,Sorghum-sudangrass hybrid cultivars have different responses in production performance,yield,quality and root soil quality,and the right choice is appropriate can not only improve the yield but also restore the soil quality.It is suggested that the 3-year-old alfalfa rotation should be selected in Jianghuai area.The rotation of Sorghum-sudangrass hybrid can restore the soil capacity,improve the soil quality,and the corn is good at improving the alfalfa yield.After the alfalfa stubble,PK has a better ability to restore the soil quality.Therefore,the appropriate cultivation measures can not only improve the soil quality but also improve yield and quality.