Speciation Transformation Of Selenium From Different Sources In Mushroom Bran Compost And Its Availability In Soil

Applying selenium fertilizer to non-selenium-enriched soil and improving selenium activity in natural selenium-enriched soil can indirectly and effectively increase selenium content in plants.However,compared with inorganic selenium fertilizer,organic selenium fertilizer has higher crop and environmental safety.The waste bran of selenium-enriched edible mushrooms contains a large amount of selenium,and it is rich in nutrients,which is a highly potential material for making selenium-enriched organic fertilizer.Meanwhile,it is also a method to make selenium-enriched organic fertilizer by applying exogenous inorganic selenium to non-selenium-enriched mushroom bran through composting process.However,the speciation transformation of selenium from different sources during composting and its differences remain to be explored.Therefore,in this study,selenium-enriched and non-selenium-enriched mushroom bran produced by the cultivation of selenium-enriched Pleurotus eryngii were taken as the research objects,and the transformation of selenium content and forms of selenium-enriched mushroom bran and two kinds of exogenous selenium-enriched mushroom bran(obtained by applying exogenous inorganic sodium selenite and sodium selenite to the non-selenium-enriched mushroom bran)during composting was explored,and the effectiveness of selenium in organic selenium fertilizer produced by composting of mushroom bran containing different sources of selenium were evaluated.At the same time,the organic fertilizer of mushroom bran was applied to non-selenium-enriched soil with different physical and chemical properties,and the non-selenium-enriched mushroom bran was applied to natural selenium-enriched soil to explore the changes of soil selenium speciation distribution and availability.The main results were as follows:1.Selenium-enriched mushroom bran and two kinds of exogenous selenium mushroom bran can be composted into selenium-enriched organic fertilizer which meets the requirements of composting products.Due to the “concentration effect”,the selenium concentration of all three kinds of selenium-riched brans increased at the end of composting.After the end of sodium selenite-mushroom bran compost(Se(Ⅳ)-SMS),sodium selenite-mushroom bran compost(Se(Ⅵ)-SMS)and natural selenium-enriched mushroom bran compost(Se-SMS),the total selenium concentration increased by 30.77%,25.76% and27.26%,respectively.Judging from the changes of temperature,p H,GI,DOC contents and DOM structure and composition,the indexes of the final composted products met the requirements of composting maturity and bio-harmlessness,and all three seleniums increased the degree of compost humification to different degrees.2.The transformation of selenium speciations during composting is related to the sources and species of selenium.In the composting process,selenium in the three kinds of selenium-containing mushroom bran mainly exists in residual selenium and organic combined state.The proportion of available selenium(SOL-Se and EXC-Se)in Se(Ⅳ)-SMS is higher than that in Se(Ⅳ)-SMS and Se(Ⅵ)-SMS.The proportion of available selenium in Se(Ⅳ)-SMS and Se(Ⅵ)-SMS compost increased first and then decreased with composting time,while the proportion of available selenium in Se-SMS treatment decreased gradually.After composting,the proportion of available selenium in sodium selenite-mushroom bran compost increased by 17.75%,while the proportion of available selenium in sodium selenitemushroom bran compost and natural selenium-enriched mushroom bran compost decreased by 46.44% and 63.83% respectively.The proportion of OM-Se in the three kinds of selenium-containing mushroom bran decreased first and then increased,and the change trend of the proportion of selenium forms in OM-Se was basically the same,that is,the proportion of HA-Se increased,while the proportion of Hy-Se and FA-Se decreased.In addition,the proportion of residual selenium(RES-Se)in the three kinds of selenium-containing fungus chaff during composting showed an increasing trend,and the proportion of Se-SMS treatment was the highest.It shows that compost can promote the transformation of selenium in fungus chaff to a more stable form,and the selenium in selenium-enriched fungus chaff compost is less effective than that in exogenous selenium fungus chaff compost.3.The change of selenium speciation distribution in Yangling Lou soil and Hunan krasnozem was influenced by the types of organic fertilizer and soil types.The application of non-Se-enriched mushroom bran compost reduced the proportion of SOL-Se(0.41～3.78%)and EXC-Se(1.42～5.65%)in Lou soil.Applying two kinds of exogenous selenium compost(Se(Ⅳ)-SMS and Se(Ⅵ)-SMS)significantly reduced the proportion of SOL-Se and EXC-Se in Lou soil,and increased the proportion of OM-Se.However,the proportion of SOL-Se and OM-Se in red soil was increased,and the proportion of EXC-Se was decreased.Regardless of the soil type,the application of Se-enriched mushroom bran compost(Se-SMS)significantly reduced the proportion of available Se in the two tested soils and increased the proportion of OM-Se.It has no concern with soil type and compost type of mushroom bran,and the application of selenium-containing mushroom bran compost significantly increases the proportion of HA-Se in OM-Se.And with the increase of composting time,the proportion of HA-Se increased first and then decreased,while Hy-Se and FA-Se gradually transformed into more stable HA-Se and HON-Se.From the change of MF value of soil selenium,it can be seen that the application of selenium-enriched mushroom bran compost reduces the availability of selenium in Lou soil and red soil to varying degrees.Selenium speciation in mushroom bran organic fertilizer and soil physical and chemical properties(p H,EC and DOC content)are all factors affecting the transformation of soil selenium speciation.4.The changes of selenium speciation distribution in natural selenium-enriched soil were related to soil properties and pretreatment methods of applied bran.Compared with the control treatment,non-selenium-enriched mushroom bran treated by composting(C-SK-SMS)and natural stacking(S-CK-SMS)increased the proportion of SOL-Se(0.30-3.85%)and OM-Se(2.01～25.04%)in Yichun soil,and decreased the proportion of EXC-Se(0.33-7.52%)in Yichun soil.But it only slightly increased the proportion of SOL-Se in Ziyang yellow brown soil(0.14～0.42%)and decreased the proportion of EXC-Se(0.12～1.43%).Judging from the change of soil selenium MF value,the application of C-CK-SMS treatment improved the availability of selenium in Yichun red soil(and the effect was better with low application amount),while the effect of S-CK-SMS treatment was opposite.Regardless of the soil type,the application of non-selenium-enriched mushroom bran with different pretreatment significantly increased the proportion of HA-Se in soil OM-Se(4.15～51.08%),and its proportion was positively correlated with the application amount of mushroom bran.And the application of C-CK-SMS treatment is higher than that of S-CK-SMS treatment,which is related to the large amount of humus produced during composting.The distribution and availability of selenium in natural selenium-enriched soil are related to the physical and chemical properties of selenium in selenium-enriched soil,such as its occurrence form,p H value,DOC content and soil organic matter content.In conclusing,Se-enriched mushroom bran and two kinds of exogenous selenium-containing mushroom bran can be made into Se-enriched organic fertilizer which meets the requirements of composting products,and the transformation of Se forms during composting is related to the source and type of Se.The application of selenium-enriched mushroom bran compost reduced the availability of selenium in Shaanxi Lou soil and Hunan krasnozem to varying degrees.The effect of applying non-selenium-enriched mushroom bran on the distribution and availability of selenium in natural selenium-enriched soil is related to soil physical and chemical properties and pretreatment methods of mushroom bran.Therefore,all factors should be considered comprehensively in the practical application of selenium bioaugmentation.