Study On The Characteristics Of Biochar Coated Urea And Its Application Effect In Black Soil

Common fertilizers have problems such as easy nutrient leaching,low fertilizer utilization,and severe resource loss.In addition,lost nutrients enter the environment,increasing the burden on the environment,and causing food security risks and environmental pollution.To solve this problem,slow and controlled release fertilizers have emerged,and have received widespread attention from relevant researchers.Using biochar as a slow-release material and taking advantage of its special physical and chemical properties such as porosity and large specific surface area,combining biochar with ordinary fertilizers can not only delay the release rate of nitrogen,but also reduce the loss of soil nutrients,thereby reducing environmental pollution.In this paper,four kinds of biochar coated urea（CU1,CU2,CU3,CU4）were prepared using corn straw biochar as coating material and rosin anhydrous ethanol solution of different concentrations as binder.The nitrogen release laws and environmental factors were investigated through static water culture test,micro diffusion test,and soil column leaching test.Thermogravimetric analysis（TG）,X-ray powder diffraction（XRD）The structure of biochar coated urea was analyzed and characterized by Fourier transform infrared spectroscopy（FTIR）and scanning electron microscopy（SEM）.Pot experiments were conducted to study the agronomic and environmental effects of biochar coated urea in black soil.The results showed that:（1）Four types of biochar coated urea CU1,CU2,CU3,and CU4 were prepared,with biochar coating amounts of 3.4%,4.8%,7.8%,and 8.6%,respectively.In the hydrostatic culture experiment,the nitrogen accumulation and release rates of the four biochar coated urea decreased by 2.3%to 11.5%compared to ordinary urea.In the soil column leaching test,the cumulative release rates of four biochar coated urea in chernozem soil decreased by 5.5%to17.0%compared to ordinary urea;The cumulative release rate in windblown sand soil decreased by 4%to 20%;The cumulative release rate in black soil decreased by 1.9%to 15.7%.In the agar diffusion test,the diffusion diameter of four biochar coated urea was reduced by 5.03 mm to11.92 mm compared to ordinary urea.This indicates that biochar coated urea has a good slow release effect compared to ordinary urea,and with the increase of the coating amount,the slow release performance of biochar coated urea is better.（2）TG analysis shows that:The thermal stability of the four types of biochar coated urea was improved compared to ordinary urea,but the thermal stability decreased as the amount of biochar coated urea increased.XRD analysis results indicate that:The higher the intensity of characteristic peaks in CU3 and CU4,the greater their crystal cell parameters and crystal plane spacing.FTIR Analysis shows that:The infrared spectrum of urea coated with biochar varies with the ratio of membrane materials at different concentrations,with CU4having the highest transmittance.SEM observation found that:The surface of the four biochar coated urea is covered with a layer of blocky or granular substances,among which the surfaces of CU1,CU2,and CU3 are stacked and rough,while the surface of CU4 is relatively smooth and the blocky or granular substances are relatively uniform.This indicates that under the action of biochar and adhesive,the surface of urea particles is covered with biochar.Among them,the biochar treated with CU4 has the most uniform coverage,forming a barrier that prevents water molecules from entering the interior of the biochar coated urea,So as to achieve the corresponding slow release effect.（3）All three environmental factors have an impact on nutrient release from coated urea,and field water capacity is the most influential of the three environmental factors on nutrient release from biochar coated urea.When the field water capacity increased from 20%to 80%,the nitrogen accumulation and release rate of biochar coated urea also increased gradually;Temperature has a significant impact on nutrient release from biochar coated urea.When the culture temperature rises from 20℃to 35℃,the cumulative nitrogen release rate of biochar coated urea increases;Increasing or decreasing soil p H will affect the cumulative nitrogen release rate of biochar coated urea.（4）Compared with conventional urea,the plant height of Chinese cabbage increased by0.23%to 8.8%with four biochar coated urea;The yield of pakchoi increased by 7.3%,12.0%,19.2%,and 28.8%,respectively,in the order of CU4>CU3>CU2>CU1;The nitrate content of pakchoi decreased by 26.1%,15.8%,7.3%,and 2.2%,respectively;The SPAD value of pakchoi increased by 5.4%to 27.7%with four kinds of biochar coated urea;The soluble sugar content of pakchoi increased by 6.3%～51.0%;The vitamin C content of pakchoi increased by 1.8%to30.9%;The nitrogen utilization efficiency of the four biochar coated urea increased by 4.0%to17.5%;The nitrification inhibition rates of the four biochar coated urea were 0.18%,0.71%,1.75%,and 2.7%,respectively,and the apparent nitrification inhibition rates decreased by 1.6%to 4%compared to the treatment U;At the same time,four kinds of biochar coated urea can improve soil urease and catalase activities in different growth stages of Chinese cabbage,among which,the urease activity increased by 2.2%to 42.9%,catalase increased by 3.3%to 21.1%,and sucrase activity increased by 8.4%to 56.7%at 45 days of harvest of Chinese cabbage.Biochar coated urea CU1,CU2,CU3,and CU4 can significantly reduce the cumulative emissions of N₂O,CO₂,and CH₄.Compared with ordinary urea U,the cumulative emissions of N₂O have significantly decreased by 18.7%,28.5%,41.3%,and 46.3%,while the cumulative emissions of CO₂ have significantly decreased by 48.5%,52.1%,54.2%,and 58.8%,and the cumulative emissions of CH₄ have significantly decreased by 8.8%,17.9%,21.7%,and 24.6%.In summary,biochar coated urea can improve the yield and quality of pakchoi,while also improving soil urease and catalase activities,reducing greenhouse gas emissions,with CU4being the best.