| Corn is the main grain crop in China,and as of 2018,the total corn output in China was70% of the total grain output.Straw as a main by-product of corn has a huge output.With the promotion of environmental protection concepts and national policies,the return of straw to the field has gradually emerged.As a new application technology,straw returning to the field is of great significance to the change of the ecological environment.With the development of modern agriculture,more and more different ways of returning straw to the field have emerged,which have also had a certain impact on the corn industry.There are many types of diseases that occur during the growth of corn.Among them,corn spot disease(Exserohilum turcicum)and corn sheath blight(Rhizoctonia solani Kühn)are the main diseases of corn.They are widespread and widely distributed,and they cause serious harm to the corn industry.The change of the method of returning straw to the field has led to changes in the law of disease occurrence.Therefore,it is of great significance to carry out research on the epidemic impact and mechanism of the method of returning straw to the field.In this paper,the occurrence mechanisms of corn sheath blight and corn leaf spot were studied under different straw returning methods.No-till mulch,pine and palladium mixing,straw crushing and deep turning,and conventional models against corn sheath blight were monitored through field disease investigation.And the rule of occurrence of spot disease,by measuring the physical and chemical properties and enzyme activity of the soil plough layer,revealing the changes of the soil environment;using high-throughput sequencing method to determine the soil fungal community,combined with soil environmental factors for correlation analysis.This study lays a theoretical foundation for revealing the biological mechanism of returning straw to the field and its impact on the occurrence of diseases,which is of great significance for the sustainable development and utilization of farmland soil resources.The main findings are as follows:1.The epidemic pattern of corn returning to corn sheath blight and leaf spot disease was clarified.Based on the principle of plant disease epidemiology and the method of random sampling investigation,the occurrence rules of corn sheath blight and spot diseasewere studied,the epidemic curve was drawn,the epidemic model of disease was constructed,and the epidemic period of disease was derived.The results show that the straw returning method has a significant effect on the occurrence of diseases.As for the degree of disease occurrence,corn leaf spot disease and sheath blight disease of corn stalk crushing and deep turning were the lightest,and the no-tillage and mulching disease occurred the most.Throughout the growing season of corn,the method of returning straw to the field has a significant effect on the occurrence of corn sheath blight in various periods,while the occurrence of maize leaf spot disease is only significant during the exponential growth period,and is not significant in other periods.Using SPSS 22.0 software to simulate the time epidemic curve of corn sheath blight in the field,it is found that the Logistic model can better simulate the epidemic curves of corn sheath blight and spot disease.Through Logistic model simulation,the epidemic period of the disease is dynamically predicted with the time change of the disease index.The change rule of maize spot disease during the epidemic period is the same as that of sheath blight.2.The change law of soil returning method to soil physical and chemical properties was clarified.Through systematic monitoring of soil physical and chemical properties,it was found that the method of returning straw to the field had a significant effect on it.With the increase of time,the soil p H increased,and the p H value of no-till mulch was the largest,and it stabilized after reaching the maximum on August 15,with the maximum value being 6.53.The EC value showed a downward trend as a whole,and the depth of crushing and deep turning decreased to a large extent,and the law of presenting was no-tillage mulching>pine-palladium mixing> crushing and deep turning> conventional mode.The porosity of the soil increased significantly,the depth of straw crushing increased by 7.2%,the mixing of pine rakes increased by 4.1%,and the level of no-till cover increased by 2.1%.Compared with the conventional model,soil bulk density straw crushing and deep turning are reduced by 13%,pine rake mixing is reduced by 11%,and no-till cover is reduced by 7%.In the no-tillage mulch layer,available potassium increased by 27.1%,available phosphorus increased by51.4%,and alkali-decomposed nitrogen increased by 39.4%.The available potassium in the plough layer of the loose rake mixed soil increased by 11.3%,the available phosphorusincreased by 24.3%,and the alkaline nitrogen content decreased slightly by 20%.Straw crushing and deep-turning the plough layer reduced available potassium by 5.9%,available phosphorus by 46.8%,and alkali-decomposed nitrogen by 31.1%.There was no significant difference in conventional models.Compared with other treatments,the average soil temperature under no-tillage treatment is higher than other treatments in the same soil layer.Through analysis of the correlation with the disease,it is found that the soil temperature and humidity are significantly related.3.The change law of soil enzyme activity after returning straw to the field was clarified.Studies on soil urease,alkaline phosphatase,catalase and invertase activities in the topsoil of the soil after the straw was returned to the field showed that the effect of straw return on the soil enzyme activity was significantly different.The methods of returning straw to the field all promote the activities of soil urease,invertase,alkaline phosphatase and catalase.The soil alkaline phosphatase activity showed the regular pattern of 0 days after sowing,and the regular pattern <straw crushing and deep turning <pine-palladium mixing<no-tillage mulch.With the increase of time,the law presented at 120 days after sowing was straw crushing and deep turning <conventional mode <pine-palladium mixing <no-tillage mulch.The change of soil urease activity in the whole growing season showed the rule of pine-palladium mixing> crushing and deep turning> no-till cover> conventional mode.Compared with other treatments,the soil invertase activity of conventional model was 40.0%higher than that of other treatments,33.0% increase of pine rake mixing,and 23.1% increase of no-till cover.The soil catalase enzyme activity reached its maximum value on July 15 th.Compared with the conventional model enzyme activity,the other methods of returning farmland increased by 37.2% in no-tillage mulching,the straw deep crushing increased by31.2%,and pine-palladium mixing increased by 18.8%.For different soil layers,as the depth of the soil layer increases,soil enzyme activity decreases.Correlation analysis revealed significant correlation between catalase and disease occurrence.4 The change law of soil fungal community under the way of returning straw to the field was explored.The high-throughput sequencing method was used to study the effect of returning straw to the soil on the fungal structure of the topsoil.The results showed that thesaprophytic fungi in the soil after no-tillage mulching,straw crushing and deep turning,and pine rake mixing treatment increased significantly.As time increases,the soil fungal abundance increases.At 0d sowing,the structure of each treatment group was significantly different.The richness and diversity of the bacteria group were the highest after the straw was crushed.A total of 15 genera were classified at the genera level.Among them,Guehomyces cold-tolerant yeast genus accounted for 67% of the entire community,Solicoccozyma spp.10%,and unknown genus Unclassified 12%.Guehomyce accounted for the largest proportion of pine-palladium mixing,and the smallest proportion of crushing and deep turning.At 45 days after sowing,the richness of straw-collapsed deep-turned colonies was the highest.With the increase of the time of returning to the field,the structure of the soil flora changed.Eight new species were added.Fusarium and Humicola accounted for 40%.At 90 days after sowing,the maximum colony abundance of each treatment was the normal mode,and the overall colony abundance and diversity increased.Compared with the 45 th day,the community structure of the genus of bacteria increased by 6 genus,of which Epicocum spp.Accounted for 70% of the newly added genus.CCA analysis showed that the three groups of no-tillage mulch,pine rake mixing and straw crushing and deep turning were far away from the spatial distribution of fungal microorganisms and available nutrients and other phenolic acid treatments,which were mainly related to no-till mulching and straw turning and deep turning It is far away from the conventional model and pine rake mixing.The soil structure is very different between the treatments.The change of the soil structure changes the fungal structure.According to soil fungal phylogeny and Heatmap analysis results,it can be seen that pine rake mixing and straw crushing and deep turning fungal communities have certain similarities. |
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