Effects Of Different Spent Mushroom Substrate(SMS)Combined With Chemical Fertilizer On Soil Nutrients,Heavy Metals And Microbial Community In Maize-Wheat Rotation

With large annual yield and high organic matter content,spent mushroom substrate(SMS)has great potential to replace part of chemical fertilizer in agricultural production.However,there are few reports on the effects of different SMS combined with chemical fertilizer on soil nutrient and heavy metal pollution.Therefore,under the field experiment of maize-wheat rotation,this study studied the effects of three different SMS combined with chemical fertilizer on soil nutrients,heavy metals and microbial communitiy,and explored the rational application scheme of SMS,so as to provide basis for the efficient and safe utilization of SMS in Chengdu plain.The experiment set up eight treatments,including no fertilizer(CK),chemical fertilizer(CF),Enoki mushroom residue instead of 25 %N(EMR1),Enoki mushroom residue instead of 50 %N(EMR2),Agaricus bisporus residue instead of 25 %N(ABR1),Agaricus bisporus residue instead of 50 %N(ABR2),Auricularia auricula residue instead of 25 %N(AAR1)and Auricularia auricula residue instead of 50 %N(AAR2).The experiment was carried out for two consecutive years to achieve nitrogen balance with fertilizer supplement.The changes of soil nutrients,the total amount and morphological changes of heavy metals(Cd,Pb,As),and the community structure of soil bacteria and fungi were studied in the soil at the maturity stage of maize and wheat in the second year.The main research results are as follows:(1)The soil organic matter content and the availability of nitrogen,phosphorus and potassium could be improved by the treatment of SMS combined with chemical fertilizer,among which AAR1 and AAR2 had the best effect.AAR1 treatment had the best effect on soil organic matter content,which increased by 13.30 % and 19.86 % in maize and wheat seasons,respectively.Compared with CF treatment,SMS combined with chemical fertilizer did not significantly increase the contents of TN,TP and TK in soil,but it could increase the contents of soil available nutrients(AN,AP and AK).Among them,AAR1 and AAR2 had the best effect on the improvement of soil available nutrients,which increased AN by 2.84 ～9.87 %,AP by 10.61 ～ 19.09 % and AK by 8.69 ～ 14.44 % in maize and wheat seasons.(2)The content of heavy metals Cd,Pb and As introduced into the soil was effectively reduced and the proportion of Cd,Pb and As residues was increased.The residue content of As is the main form,accounting for 74.80 ～ 78.75 % of the total.Pb morphology is mainly reducible state and residual state.However,the proportion of residual Cd is low,accounting for 13.95 ～ 35.99 % of the total,indicating that the content of available Cd in soil is high,and the pollution risk is high.Compared with the residue state of Cd treated by CF(13.95 ～ 17.68 %),the residue state proportion of heavy metals could be increased by SMS combined with chemical fertilizer,among which the ABR1 and ABR2 was the best,the residue proportion of Cd treated by ABR1 and ABR2 was 29.19 ～ 32.03 %,32.01 ～ 35.99 %,respectively.(3)The bacterial community structure in soil could be changed by the treatment of SMS combined with chemical fertilizer,and α-diversity of soil bacterial community could be significantly increased in wheat season,especially EMR2 treatment.In the maize season,α-diversity of bacterial community was significantly different among different treatments.Actinobacteria,Proteobacteria and Acidobacteriota were the dominant bacterial communities in both maize and wheat seasons.Soil Cd,Cd-a,Pb-b,Pb-c,As-c and Cd-d were the main soil environmental factors affecting the bacterial community in maize season,while the bacterial community in wheat season was significantly affected by OM,TN,TK,AN,AP,AK and Cd.(4)The SMS combined with chemical fertilizer could change the structure of soil fungal community,and ABR2 treatment significantly increased the α-diversity of the fungal community in the wheat season.There was no significant difference in α-diversity among treatments during wheat season.Ascomycota and Mortierellaomycota were the dominant phylum in the fungal community in both maize and wheat seasons.Soil AK,Cd,Pb,Cd-a,As-a,Pb-b,Pb-c,As-c and Cd-d were the main soil environmental factors affecting the fungal community in maize season,while the fungal community in wheat season was mainly affected by Cd-c and As-c.In conclusion,SMS combined with chemical fertilizer can effectively improve the availability of soil nutrients,fix soil heavy metals,reduce the mobility of soil heavy metals,and improve the diversity of soil microbial community.However,the effects of different SMS application treatments vary greatly.In terms of production suggestions,considering soil fertility,Auricularia auricula residue with better effectiveness in improving soil nutrient content and availability should be selected.In order to reduce the availability of heavy metals in soil,Agaricus bisporus residue with better effect of reducing the mobility of heavy metals in soil should be selected.In terms of the substitution proportion of SMS,25 % of nitrogen should be substituted by SMS.