Effects Of Sulfur/polymer Coated Urea On Wheat Agronomic Benefits And Soil Microbial Community

The filling stage is a vital stage for wheat（Triticum Aestivum L.）yield formation.At this stage,leaf senescence can be delayed and photosynthesis promoted under sufficient nitrogen supply.Urea,as a high nitrogen fertilizer,can provide nutrients for wheat growth,but its nutrients are easy to volatilize,leaching and lose,which resulted lacking fertilizer and premature aging in the middle and late stages of crop growth,thus reducing efficiency.Controlled release urea（CRUs）,including polymer-coated urea（PCU）,sulfur-coated urea（SCU）,and polymer/sulfur dual layer-coated urea（PSCU）,is designed to release N into the soil solution at rates which closely match the N demands of crop,thus increasing crop yield and nitrogen use efficiency,which is one of the means to reduce agricultural production costs and improve comprehensive benefits.Therefore,investigating the effects of mainstream controlled-release urea products on soil nutrient supply and microorganism community at wheat filling stage is great significance for improving the mechanism of increasing yield and efficiency and accelerating its popularization and application in wheat.In this study,the effects of 3 kinds of CRUs on the ecological function of soil environmental factors in 2021 were studied under wheat-maize rotation for 12 years and 24seasons,with the application of urea as control for comparison.Meanwhile,the change characteristics of soil microbial functional communities were revealed by using High-throughput sequencing technology.Besides,the coupling relationship between soil nutrient supply,functional microorganisms and wheat yield was determined by structural equation modeling.The main results were showed that:（1）Soil acidity and nutrient content at filling stage were significantly affected by the long-term application of sulfur/polymer-coated urea.Compared with urea treatment（U）,soil exchangeable Ca²⁺and Mg²⁺contents were significantly decreased,but the contents of soil hydrolytic acidity,exchangeable acidity and exchangeable hydrogen were significantly increased in sulfur-coated urea（SCU）,and polymer/sulfur dual layer-coated urea（PSCU）,which resulted in the decrease of soil p H value.On the other hand,the loss of soil exchangeable Ca²⁺was decreased to alleviate soil acidification in the polymer-coated urea（PCU）treatment.In addition,3 kinds of CRUs were better than common urea in improving soil fertility,in which the contents of soil matter organic and total nitrogen were significantly enhanced by 3.1%～5.0%and 13.4%～20.1%,respectively.At the same time,the average yield and net income were significantly increased by 12.4%～22.8%and 22.8%～39.2%in the CRUs treatments,respectively.（2）Soil carbon,nitrogen and sulfur cycling enzyme activities were significantly enhanced by the long-term application of sulfur/polymer-coated urea,thereby promoting soil nutrient cycling.Compared with U,soil cellulase activity was significantly increased in all CRUs treatments.The activities of hemicellulose andβ-galactosidase were not significantly different in PCU,but were significantly higher in SCU and PSCU.For the N cycling-related enzymes,the activities of hydroxylamine oxidoreductase,urease,andβ-acetylglucosaminidase were significantly increased by 14.6%～16.8%,6.6%～32.1%and 4.8%～13.0%in all CRUs treatments,respectively.Besides,the activities of nitrate reductase and nitrite reductase were enhanced in all CRUs treatments,which promoted the transformation of soil nitrogen.In addition,the activities of S cycling-related arylsulfatase,sulfite reductase and sulfite dehydrogenases were significantly higher by 2.5%～3.7%,12.3%～19.4%and 10.6%～14.9%in all CRU treatments.The activity of thiosulfate reductase in SCU and PSCU was significantly higher by 4.1%and 18.6%,respectively.（3）Soil microbial community composition was significantly changed by the application 3kinds of CRUs.According to the results of principal coordinate analysis,the bacterial and fungal community structures in SCU and PSCU were similar but were significantly separated from the other nitrogen treatments,which indicated that the microbial community composition could be affected by sulfur.In addition,FAPROTAX prediction results indicated some functional groups abundances involved in carbon,nitrogen,and sulfur,such as methanol oxidation,cellulolysis,methylotrophy,nitrogen fixation,dark oxidation of sulfur compounds,and dark thiosulfate oxidation,were significantly increased by the application of SCU and PSCU.Meanwhile,the abundances of anoxygenic photoautotrophy and anoxygenic photoautotrophy S oxidizing were significantly increased by the application of PCU,compared with other treatment.In the fungal community structures,FUNGuild results showed that the abundances of animal pathogen and plant pathogen were significantly decreased under the application of CRUs,which indicated that CRUs restrained the growth of pathogen,and then reduced the risk of soil-borne disease.（4）The microbial co-occurrence relationship was significantly affected under the long-term application of sulfur/polymer-coated urea.The results of microbial co-occurrence network showed that the relative abundance of beneficial microorganisms of bacterial and fungal ecological cluster 1 was significantly increased in CRUs than in U.At the same time,the relative abundance of pathogenic microorganisms of bacterial and fungal ecological cluster 2 was decreased in CRUs,compared with U.The random forest prediction model demonstrated that the relative abundance of fungal modules 2,and the relative abundance of bacterial modules 1and 2 were the most important predictors of wheat yield.Finally,structural equation modeling revealed that soil ammonium nitrogen indirectly stimulated the growth of plant growth-promoting microorganisms in the module 1 of bacterial co-occurrence network and inhibited the activity of plant pathogenic microorganisms by promoting soil matter organic accumulation,which provided an adaptive environment for wheat growth,thus increasing yield and income.In conclusion,the long-term CRUs application can promote soil nutrient conversion and stimulate the growth of beneficial microorganisms by improving soil carbon,nitrogen,and sulfur cycling enzyme activities,which provide a suitable environment for wheat roots nutrient uptake.In addition,the soil nutrient conversion efficiency and growth promotion ability of beneficial microorganisms in SCU and PSCU were better than in PCU.