Effects Of Exogenous Imported Organic Fertilizers With Different Degrees Of Maturity On Carbon Effect And Properties Of Salinized Soil

Soil organic carbon content is the core index of soil fertility.The application of organic fertilizer is an important measure to increase soil organic carbon content,improve soil fertility and improve salinized soil.However,in agricultural production,it has always been considered that only fully decomposed organic fertilizer should be applied into soil,but fully decomposed organic fertilizer has a long fermentation cycle,serious loss of nutrient and carbon,and reduced fertilizer efficiency after application in soil,affecting crop growth.The carbon source and physicochemical properties of organic fertilizer at different stages of maturation are different,and individual application constituted different organic fertilizer cultivation measures.However,the mechanism of sequestration and influence of these fertilization measures on organic carbon remains unclear.Therefore,it is of great practical significance to carry out relevant research on the fermentation control of organic fertilizer and rational fertilizer cultivation.Therefore,this study prepared undecomposed organic fertilizer,high temperature organic fertilizer,cooling temperature organic fertilizer and decomposed organic fertilizer by self-heating aerobic compost,and conducted simulated fertilizer cultivation experiment on salinized soil after finding out its basic physical and chemical properties.Systematically studied the effects of different degrees of maturation of organic fertilizer and different amounts of fertilizer application on organic carbon retention.The response mechanism of different organic fertilizer inputs to carbon fixation in salinized soil was investigated from the aspects of physical and chemical properties,organic carbon timing changes,carbon components,organic carbon mineralization,aggregate distribution and stability,soil microbial community structure and diversity.The main findings are as follows:1.The self-heating aerobic compost lasted for 43 days.Organic matter decomposed with the composting process and the organic carbon content and C/N of the reactor were gradually reduced.The content of p H,total nitrogen,total phosphorus,total potassium,available phosphorus,available potassium were increased.The percentage of available phosphorus and available potassium of organic fertilizer in total phosphorus and total potassium was the highest in the cooling period.With the composting process,the conductivity first decreased and then increased,and the order from large to small was organic fertilizer in decomposed stage>cooling temperature stage>undecomposed stage>high temperature stage.The relative contents of hemicellulose and cellulose decreased with the composting process and the relative content of lignin increased.In the changes of humic acid content,the contents of total humic acid and free humic acid decreased gradually with the composting process,and the humic acid conversion rate was the highest in the cooling period.Among the changes of humus composition,fulvic acid content decreased significantly with the composting process,humic acid content first increased and then decreased,and humic acid content was the highest in the cooling period.In the infrared spectrum structure,organic fertilizer compost was a process of aliphatic reduction,small molecular sugars and aromatic structure enhancement.The higher content of hemicellulose in compost may be the main reason for the decrease of organic carbon content.2.Four kinds of organic fertilizers with different degrees of maturation could improve soil organic carbon content and carbon sequestration efficiency,but with the increase of fertilizer dosage,soil carbon sequestration efficiency increased first and then decreased.Compared with unfertilized soil,decomposed organic fertilizer increased the amount of available phosphorus,available potassium,total nitrogen,total salt and alkalinity of soil most significantly.And the cooling period organic fertilizer increased the total phosphorus,total potassium and cellulase activities most significantly.Undecomposed organic fertilizer significantly reduced soil p H and conductivity.The application of organic fertilizer in the cooling period was the best to improve the organic carbon content and carbon sequestration efficiency of salinized soil,and the least to improve the salinization degree of soil.Total salt content,alkalization degree and urease were the main factors inhibiting the increase of soil organic carbon content.3.The contents of easily oxidized organic carbon（EOC）,microbial biomass carbon（MBC）,dissolved organic carbon（DOC）,particulate organic carbon（POC）,mineral bound organic carbon（MOC）and soil carbon pool stability index were all increased by different degrees of organic fertilizer.The EOC/SOC,DOC/SOC and MBC/SOC of undecomposed organic fertilizer and high temperature organic fertilizer were relatively high,that could significantly increase soil carbon pool activity,carbon pool activity index and carbon efficiency,that could promoted organic carbon mineralization rates and cumulative CO₂ emissions.and that’s bad for carbon storage.Decomposed organic fertilizer mainly increased the content of MOC,significantly reduced the activity of soil carbon pool and increased the carbon pool index,thereby reducing the cumulative emissions of soil CO₂,and had a good effect of carbon sequestration and emission reduction.In the cooling period,organic fertilizer had the lowest reduction rate of active organic carbon content and the highest persistence with the continuous fertilization time,and had relatively good effects on the content of active and inert carbon components in soil,which could increase both the activity of carbon pool and the index of carbon pool,and had the best effect on improving the management index of carbon pool and improving the quality of organic carbon pool.With the increase of fertilizer dosage,the contents of EOC,DOC,MBC,POC and MOC could be increased,but the ratio of EOC/SOC,DOC/SOC,MBC/SOC,POC/SOC could be decreased,and the ratio of MOC/SOC could be increased.The increase of active carbon components could promote the rate of organic carbon mineralization and the cumulative CO₂ emission.Therefore,overfertilization mainly increased the carbon pool index,but had no significant effect on the soil carbon pool management index.The contents of EOC and DOC are the key factors affecting the soil organic carbon storage and the stability of soil carbon pool.4.Compared with CK,the contents of large aggregates（>0.25mm）were significantly increased by 6.01%,6.50%and 8.87%,while the contents of micro-aggregates（<0.25mm）were significantly decreased by 9.88%,10.69%and14.60%,under the treatment of undecomposed organic fertilizer,high temperature organic fertilizer and cooling temperature organic fertilizer.The stability of aggregates was significantly enhanced,and the soil carbon sequeeration capacity was improved by increasing the organic carbon content in aggregates.Organic fertilizer had no positive effect on the formation and stability of macroaggregates,but it could inc rease the accumulation of organic carbon by promoting the distribution of organic carbon in macroaggregates 0.5-1mm,0.25-0.5mm and microaggregates<0.25mm.Under different organic fertilizer application,high fertilizer rate had no significant effect on the organic carbon content of>2mm aggregates,and mainly increased the organic carbon content of0.5-1mm and 0.25-0.5mm aggregates,and fixed the organic carbon in the fine and large aggregates.5.The microbial community of uncultivated and salinized soil was dominated by bacteria.Under different levels of organic fertilizer application,the dominant bacterial groups were Proteobacteria,Firmicutes,Actinobacteriota,Bacteroidota,Chloroflexi and Gemmatimonadota,and the dominant phylum of fungi is Ascomycota,and at the order level,the dominant bacteria were Glomerellales,unclassified＿c＿Sordariomycetes,Hypocreales,Sordariales,and Microascales.The application of organic fertilizer with different degrees of maturation had no significant effect on the soil microbial community structure,and had different degrees of influence on the relative abundance,diversity and abundance of dominant bacteria.The application of decomposed organic fertilizer can significantly reduce the shannon index and richness Chao1 index of soil bacterial diversity.The alpha diversity index of fungal in soil with four different degrees of organic fertilizer decreased significantly.Functional prediction showed that there was no significant difference in the abundance of potentially pathogenic bacteria in the application of organic fertilizer with different degrees of maturation.The cooling organic fertilizer treatment was helpful to increase oxidation stress tolerance bacteria and saprophytic trophic fungi.RDA analysis showed that organic carbon,total nitrogen,catalase,urease andβ-glucosidase in salinized soil all decreased the Shannon index of bacterial and Shannon index and Chao1 index of fungi.Bacterial abundance was inhibited by EC and MOC content.Single application of organic fertilizer indirectly regulated the composition and diversity of microbial community by affecting the carbon components and physical and chemical properties of salinized soil,and then affected soil fertility and carbon storage.In conclusion,organic fertilizer with different degrees of maturation could increase soil organic carbon content.Composting time affected the nutrient content and material composition of organic fertilizer.The properties,application amount and culture time of organic fertilizer in salinized soil affected the holding effect of organic carbon.The content of humic acid of organic fertilizer was higher and the p H was moderate during the cooling period,which significantly improved soil active carbon pool,carbon pool management index and aggregate stability.From the perspective of organic carbon retention and economy,proper addition of organic fertilizer in cooling period could improve the carbon sequestration effect of salinized soil better.