The Distribution Of Soil Microorganism And Evaluation Of Soil Fertility In Different Mixed Forests Of Dalbergia Odorifera

The effect of soil weathering and eluviation in tropical regions was strong,the regions'soil nutrients loss seriously,and soil fertility was poor.Because Dalbergia odorifera is a kind of precious leguminous plant in tropical regions,so building the mixed forests of Dalbergia odorifera can increase national wealth,also can improve poor soil in tropical regions,and improve soil fertility and forestland productivity.This paper studied the soil fertilities of Dalbergia odorifera in different mixed forests.The mixed forest of Dalbergia odorifera + Santalum album,and mixed forest of Dalbergia odorifera + Homalium hainanense,and mixed forest of Dalbergia odorifera + Spathodea campanulata,and mixed forest of Dalbergia odorifera +Aquilaria sinensis,and mixed forest of Dalbergia odorifera + Dalbergia oliveri and pure forest of Dalbergia odorifera were selected for the analysis and comparision of soil microorganisms,enzyme activities and physical,chemical properties.And the correlation between soil microorganisms and enzyme acitivity indicators,and the correlation between soil physical and chemical indicators,and the correlation between soil microorganism,enzyme activity indicators and physical,chemical indicators were analyzed.Soil fertilities of these mixed forest and pure forest were assessed with principal component analysis.This can provide a scientific and theoretical basis to building afforestation patterns and soil fertility evaluation system of Dalbergia odorifera plantation.The results were showed as the followings:(1)The ecological distribution of soil microorganisms and soil enzymes in different types of mixed forests of Dalbergia odoriferaThe three types of soil microbial quantities in all mixed forests showed that the bacterias>actinomycetes>fungis.In all mixed forests,soil bacteria quantities of Dalbergia odorifera + Santalum album were the most,which were up to 26.43×104cfu/g.However soil actinomycete quantities and fungi quantities of Dalbergia odorifera + Homalium hainanense were the most,which respectively reached 17.30×103cfu/g,5.22x103cfu/g.For total soil microbial quantities of all mixed forests,Dalbergia odorifera + Santalum album were the most,which were up to 284.45×103cfu/g,Dalbergia odorifera + Spathodea campanulata were the least,which were up to 177.69x103cfu/g.The soil microorganism population quantities of mixed forests were significantly higher than the pure forest.The soil microorganism population quantities of mixed forests followed an order of Dalbergia odorifera ?Santalum album>Dalbergia odorifera + Dalbergia oliveri>Dalbergia odorifera +Homalium hainanense>Dalbergia odorifera + Aquilaria sinensis>Dalbergia odorifera + Spathodea campanulata.The research on soil enzyme activities showed that four kinds of soil enzyme activities in each mixed forests were higher than pure forest.soil catalase activities of Dalbergia odorifera + Aquilaria sinensis were the largest,which were up to 1.29ml/g;soil acid phosphatase activeties of Dalbergia odorifera + Santalum album were the largest,which were up to 1.19mg/g.But soil urease and invertase activities of Dalbergia odorifera + Homalium hainanense were the largest,which respectively reached 0.21mg/g,15.38mg/g,it was significantly higher than other forests,which respectively were pure forest'6.17,8.54 times.(2)The rearch on soil physical and chemical properties in different types of mixed forests of Dalbergia odoriferaWith the increase of soil depth,soil water content and total soil porosity decreased,but soil buld density increased.The abilities of water-retainment and improving soil structure of five kinds of mixed forests were inmproved.Every soil physical indicators of Dalbergia odorifera + Santalum album was the best.It was compared with the pure forest,which soil water content increased by 51.65%,soil bulk density reduced by 11.24%,and the total porosity increased by 28.95%.The research on soil chemical properties showed that soil pH increased with soil depth increasing.Soil pH of all mixed forests belong to acidity at around 4.50.Soil organic matter,total nitrogen,total phosphorus,total potassium,available nitrogen,available phosphorus and available potassium contents of all mixed forests decreased with soil depth increasing.The contents of every chemical properties of five mixed forests were higher than the pure forests.Organic matter,total nitrogen,total phosphorus,available nitrogen and available phosphorus contents of Dalbergia odorifera + Santalum album were the highest,the above five nutrient indicators of Dalbergia odorifera + Santalum album were compared with the pure forest,respectively increased by 58.80%,42.71%,40.00%,13.99%,209.46%.Total potassium and available potassium contents of Dalbergia odorifera + Dalbergia oliveri were highest,which were compared with the pure forest,respectively increased by 204.17%,125.52%.(3)The analysis of correlation beween every indicators and evaluation of soil fertility in different types of mixed forests of Dalbergia odoriferaThe relationship between soil microorganism and enzyme activity indicators were closed,which presented strongly significant or significant positive correlation,and the relationship of soil microorganism,enzyme activity and soil nutrients indicators also reached significant or strongly significant positive correlation.The first principal component mainly reflected the bacteria,actinomyces,fungi,acid phosphatase,water content,total porosity,pH value,organic matter,total nitrogen,total phosphorus,available nitrogen and available phosphorus,the variance contribution rate was the largest,which reached 54.244%,so these twelve indicators played an important role in comprehensive evaluation of soil fertility.Because the second and third principal components mainly reflected the urease,sucrase,bulk density,catalase,total potassium and available potassium,the variance contribution rate was the lesser,so these six indicators became reference factors of comprehensive evaluation of soil fertility.The Integrative scores of soil fertility level were used to evaluate the soil fertility.The soil fertilities of every mixed forests followed an order of Dalbergia odorifera + Santalum album>Dalbergia odorifera + Homalium hainanense>Dalbergia odorifera + Dalbergia oliveri>Dalbergia odorifera +Aquilaria sinensis>Dalbergia odorifera + Spathodea campanulata.And the soil fertilities of every mixed forests were higher than the pure forest.So the mixed forest of Dalbergia odorifera + Santalum album was the most suitable mixed mode that can effectively improve the soil fertility,this mixed mode was worth of promoting.