Characteristics Of Organic Cementing Material And Its Effect On ¹⁵NUE Under Structural Change Of Black Soil

The soil structure has been seriously harmed as a result of unreasonable land usage.The absorption and utilization of nutrients by crops is directly influenced by the quality of the soil structure,which has an impact on crop yields.Increasing the efficiency of fertilizer usage,reducing soil damage,and lowering the negative impact of land use on the environment are all major concerns facing agriculture around the world.Chinese black soil quality and crop nutrient utilization have declined.Improving soil structure is the key to improving the quality of black soil and the utilization of crop nutrients.Soil cementing substances is the main factor to effect the structure of black soil.How to define the difference in soil structure,as well as the difference between the cementing substances and the utilization of nutrients under different black soil structures,remains to be explored.Because direct preparation and identification of soil structure is very difficult,we created three research access points to study the black soil structure under different changed ways :（1）The soil treated with different application amounts of biochar represents the different soil structures as a background for research;（2）Use dry sieving treatment,and conduct research on the background of artificially creating different soil structure with different sieving treatments;（3）Use three different land use methods（bare field,conventional tillage,natural growth）as a background for research.Three groups of different soil structure background tests were organized using the above three research access points,and the¹⁵N tracer method was used to investigate the difference in the influence of the black soil structure and ¹⁵N utilization efficiency.Explore and establish the relationship among the soil structure,cementing substances,¹⁵N utilization efficiency.Provide a theoretical foundation for enhancing soil structure to boost nitrogen fertilizer utilization efficiency.In this study,the physical properties of soil（compactness,bulk density,water content,aggregate）,soil cementing substances（soil organic carbon,humic acid,hummin,polysaccharide,and glomalin-related soil protein）,the absorption of ¹⁵N fertilizer by maize,soil nitrogen（total nitrogen,alkali-hydrolyzed nitrogen）,and retention and loss of ¹⁵N fertilizer in soil were measured by three groups of experiments（different application amounts of biochar,soil screening treatment,and different land use methods）.The research results were as follows:（1）The application of biochar can significantly improve the physical properties of the soil and increase the soil’s ability to maintain and supply fertilizer.The application of biochar can significantly reduce soil compactness and soil bulk density.As the amount of application increases,the soil bulk density decreases.The application of biochar can significantly increase the soil moisture content in the first year,and P24(application rate 24 t ha^-1)is the best treatment.With the increase of planting years,the soil moisture content will have a downward trend,the physical structure difference between different application rates will be reduced,and the improvement effect of biochar on soil physical properties will be reduced;Adding biochar to the soil improves the ¹⁵N absorption and utilization efficiency of corn,and the ¹⁵N absorption capacity of corn leaves and grains is enhanced,which significantly increases the pigment content of corn plant leaves,promotes the growth of corn roots,and improves corn yield.The soil total nitrogen,alkali hydrolyzable nitrogen content,and ¹⁵N retention potential have all been significantly improved.However,when the application rate of biochar is high(48 t ha^-1),the positive effects of ¹⁵N utilization rate of corn and ¹⁵N retention rate of soil will be weakened;The application of biochar significantly changes the content of cementing substances in the soil,and polysaccharides,SOC,HA,and HM will increase with the increase of the amount of biochar.At the same as the degree of condensation,thermal stability,and aromaticity of soil HA and HM are enhanced,and the molecular structure tends to be stable.However,the application of biochar limit the production of GRSP.With the increase of planting years,the difference in the cementing substances contents among the various biochar treatments decreased.（2）The large-grain sieving C treatment（2-10 mm）and middle-grain sieving B treatment（0.5-2 mm）can significantly reduce soil compactness and bulk density,and increase soil moisture content.The soil compactness and bulk density of the small-grain sieving A treatment（<0.5 mm）increased,while the moisture content decreased significantly;as the planting year increased,the difference between all treatments decreased;Sieving treatments B and C increased the ¹⁵N absorption and utilization efficiency of maize,and the absorption capacity of leaves and grains increased.Screening treatment A hindered the absorption and utilization of nitrogen by corn and reduced the utilization rate of¹⁵N fertilizer.Treatments B and C increased the leaf pigment content of maize leaves,promoted the growth of roots,and increased the yield,while treatment A was the opposite.Sieving treatments B and C can significantly increase the total nitrogen and alkaline nitrogen content of the soil.Within the range of the whole soil layer（0-40 cm）,the retention rate of ¹⁵N fertilizer decreases with the increase of the sieving size.The size trend of all treatments is A>CK>B>C,the adsorption and retention of ¹⁵N by HM of all treatments is stronger than that of HA,and the adsorption and retention of ¹⁵N by HA and HM are consistent with the retention law of ¹⁵N in the whole soil layer.The sieving treatments significantly changed the cementing substances contents in the soil.As the sieving size increased,the cementing substances contents increased（GRSP,polysaccharides,SOC,HA,HM）,and the oxidation degree of soil HA and HM increased.Aliphaticity is enhanced,condensation degree and thermal stability are reduced,and aromaticity is weakened.The cementing substances content of soil treated with the small-grain sieving A treatment was lower than that of CK（unsieved）treatment,and the molecular structure of HA and HM was more stable than that of CK treatment.（3）Among the different soil types of land use,natural growth treatment（NG）can significantly reduce soil compactness and bulk density,and increase soil moisture;while bare land treatment（BF）has the highest soil compactness and bulk density and the lowest moisture content;As the planting year increases,all treatment differences decrease;NG treatment increased the ¹⁵N absorption and utilization efficiency of maize,and leaves and grains had the highest absorption capacity of ¹⁵N;BF treatment hindered maize’s absorption and utilization of nitrogen,and ¹⁵N fertilizer utilization was reduced.NG treatment increased the pigment content of leaves,promoted the growth of root and increased yield,followed by conventional tillage（CT）treatment,and BF treatment was the lowest.NG treatment can significantly increase soil total nitrogen and alkaline nitrogen content,soil ¹⁵N retention rate is the highest,BF treatment soil ¹⁵N fertilizer retention rate is the lowest;The soil cementing substances content under different land use methods were also different.All cementing substances contents（SOC,HA,HM,polysaccharides and GRSP）were in the order of NG>CT>BF;BF-treated soil HA and HM molecular oxidation degree,The degree of condensation is the highest,the aromaticity is the strongest,the molecular structure was the most stable,the CT treatment was the second,and the NG treatment was the weakest.In summary,P24 treatment,C（2-10 mm）sieving treatment,and NG treatment are the best in our three studies to promote corn growth,increase corn ¹⁵N utilization,soil ¹⁵N retention,soil cementing substances and soil structure.