Effects Of Microbial Fertilizers And Different Forages On Soil Quality In Coastal Saline Soils

Nutrient deficiencies and salinity stress greatly limit the productivity of coastal saline lands in the Yellow River Delta.Microbial fertilizer is considered as potential bioamendments to address global soil security issues such as fertility loss,acidification and salinization.In this study,microbial fertilizers,Alfalfa(Medicago sativa),Sweet sorghum(Sorghum bicolor’Dochna’)and Mexican corn(Purus frumentum)were used as test materials in a two-factor completely randomized trial with fertilizer application rates(no fertilizer,low fertilizer,medium fertilizer and high fertilizer)and three grass species in the coastal saline lands of the Yellow River Delta.The effects of microbial fertilizers and different forage combinations on soil physical and chemical properties,soil enzyme activities and other soil indicators in coastal saline soils were investigated by a combination of indoor quantitative analysis and field experiments,and the effects of fertilization and forage on soil microbial community diversity,composition and structure were studied by soil high-throughput sequencing technology.Finally,the soil quality was comprehensively evaluated by using the Soil Quality Index(SQI).The main research findings are as follows:(1)Microbial fertilizer and forages improved the chemical properties of coastal saline soils significantly.Fertilizer application and forage will help to reduce soil p H and EC.The best p H reduction effect of fertilizer application is not unique to different forages;Alfalfa and Sweet sorghum reduce soil p H best at high fertilizer application rates,and Mexican corn reduces soil p H best at medium fertilizer application rates;Alfalfa,Sweet sorghum and Mexican corn all reduce soil EC best at medium fertilizer application rates.Microbial fertilizer application alone increased soil organic carbon,Available N,Available P,and Available K,and all increased with fertilizer application.Soil organic carbon tended to increase and then decrease with increasing fertilizer application after planting forage grasses.Alfalfa had the most significant increase in soil Available N compared to the other two forages.The trend of increase in soil Available P after planting Mexican corn was consistent with fertilizer application alone,both increasing with fertilizer application;Alfalfa and Sweet sorghum had the highest soil Available P content at medium fertilizer application rates.The trend of soil Available K content was basically the same as that of Available P.(2)Microbial fertilizer application alone enhanced soil catalase,sucrase and urease activities and showed an increasing trend with increasing fertilizer application,indicating a positive interaction between microbial fertilizer and soil enzyme activities.The soil microbial enzyme activities did not increase continuously with the increase of fertilizer application after planting different forages,but the optimal application rate appeared and there were differences in the optimal application rates for different forages.(3)Microbial fertilizer and forages can affect microbial communities to different degrees.Soil bacterial Shannon index differed in Alfalfa at different fertilizer application rates,and the soil bacterial diversity index Shannon index was significantly lower at medium and high fertilizer application rates compared with other treatments;Shannon index of bacterial diversity was significantly lower in Mexican corn at medium fertilizer application rates compared with other treatments.The effect of fertilizer application and forage on the soil bacterial Chao1 index was not significant.There were significant differences in soil fungal community diversity between different fertilizer applications for the same forage;there were also significant differences in soil fungal community diversity between different forages under the same fertilizer application.The dominant bacterial phylum of coastal saline soil mainly included Acidobacteriota,Proteobacteria,Actinobacteriota;the dominant fungal groups included Ascomycota,Zygomycota,Basidiomycota,Glomeromycota.Fertilization and grazing significantly increased the relative abundance of dominant microorganisms,but the effects varied.Fertilization and planting forage altered the similarity of bacterial and fungal microbial communities.The factors affecting the soil bacterial community structure in the coastal saline wasteland of the Yellow River Delta were mainly p H,AP,S＿SC,S＿CAT,AK,S＿UE and AN.The factors affecting the soil fungal community structure were mainly p H,SWC,EC,S＿CAT,AP and S＿SC.(4)Microbial fertilizer and forages will affect the soil quality level in coastal saline land,and according to the comprehensive evaluation score of soil quality,it is found that the treatments with higher comprehensive soil quality index are G4JM>G5JM>G4JH>G5JH.The comprehensive scores among the four fertilizer treatments are ranked from high to low:JM>JH>JN>JL,indicating that the improvement of comprehensive soil quality by microbial fertilizer does not increase continuously with the increase of fertilizer application.The effect of fertilizer application on the overall soil quality level was better with medium fertilizer application than with high fertilizer application,low fertilizer application and no fertilizer application;the overall scores among the three forage treatments were ranked from high to low:G4>G5>G1,indicating that the soil quality level was higher under Sweet sorghum and Mexican corn compared to Alfalfa.In addition,the soil quality level of Sweet sorghum and Mexican corn was higher under medium fertilizer application(0.24 kg/m~2)than under high fertilizer application(0.36 kg/m~2).The experiment showed that microbial fertilizer and forages are feasible solutions for restoring saline soils and improving land productivity in the coastal Yellow River Delta,moreover,the addition of microbial fertilizer should be maintained at optimal levels and this study will help to design the best microbial fertilizer application strategy for improving soil quality and land productivity for growing different forages in coastal saline soils.