Effects Of Combined Application Of Chemical Fertilizer And Biochar On Rice Yield And Soil Fertility

To investigate the effect of chemical fertilizer with biochar on rice yield and soil fertility,The experiments were conducted in 2021-2022 at the long-term positioning experimental site in gongdao town,hanjiang district,yangzhou city.The main local rice variety,nanjing3908,was used as the experimental rice variety,and the experimental chemical fertilizer were urea,calcium superphosphate,potassium chloride and rice straw biochar.The experiment was conducted in a randomized group design with three replications and six treatments:(1)no chemical fertilizer(blank),(2)chemical fertilizer alone(270 kg/ha N;75 kg/ha P2O5;150 kg/ha K2O),(3)biochar alone(12 t/ha),(4)chemical fertilizer with low amount of biochar(3 t/ha),(5)chemical fertilizer with medium amount of biochar(12 t/ha),(6)chemical fertilizer with high amount of biochar(15 t/ha).By measuring soil physical and chemical properties,soil enzyme activity,soil organic carbon fraction and rice yield in 0-5cm and 5-20cm soil layers,we clarified the effects of chemical fertilizer with biochar on rice yield and soil fertility.The main results of the experiment are as follows:1.Effect of chemical fertilizer with biochar on rice yield and soil physicochemical properties(1)Compared with chemical fertilizer alone,chemical fertilizer with different amounts of biochar increased rice yield by 3.14%～8.54%(2021)and 12.36%～18.32%(2022),with the highest rice yield with medium amount of biochar application.The increase in rice yield became larger with the increase of biochar application year.(2)Two kinds of soil layers,compared with chemical fertilizer alone,chemical fertilizer with different amounts of biochar improved soil acidification and increased TOC,OM,TN,AN,C/N,AP,AK.In 0-5 cm soil layer,a rise of 41.00%-98.08%,38.94%～91.17%,4.42%～20.88%,4.71%～12.66%,35.04%～63.15%,8.93%～65.56%,6.33%～19.00%(2021)and 37.97%～75.19%,30.66%～66.96%,3.10%～14.34%,0.14%～7.23%,and 31.84%～58.35%,8.72%～60.32%,8.07%～15.48%(2022)respectively;In 5-20 cm soil layer,a rise of 20.58%～55.36%,18.82%～42.83%,12.35%～33.33%,16.35%～30.35%,15.67%～22.64%,and 6.61%～46.03%,9.00%～11.88%(2021)and 19.24%～74.53%,17.39%～64.21%,10.77%～25.13%,0.57%～7.25%,4.03%～46.69%,5.58%～32.22%,8.74%～14.63%(2022)respectively.Compared with biochar alone,chemical fertilizer with different amounts of biochar lowered soil pH,increased AN,AP,and AK.Chemical fertilizer with low amount of biochar reduced C/N,and with medium amount of biochar increased TOC,OM and TN.(3)With the exception of soil pH,the remaining soil physicochemical indicators were greater in the 0-5 cm soil layer than in the 5-20 cm soil layer among all treatments.2.Effect of chemical fertilizer with biochar on soil enzyme activity.(1)Two kinds of soil layers,compared with chemical fertilizer alone,chemical fertilizer with different amounts of biochar reduced soil β-glucosidase activity.Chemical fertilizer with medium and high amounts of biochar increased soil invertase and urease activity.Compared with biochar alone,chemical fertilizer with different amounts of biochar increased soil urease activity;with medium and high amounts of biochar increased soil invertase activity;with low and medium amounts of biochar increased β-glucosidase activity activity.(2)In 2021,soil invertase,β-glucosidase and urease activities were greater in the 0-5 cm soil layer than in the 5-20 cm soil layer in all treatments,and the differences were not significant in 2022.Soil β-glucosidase activity was greater in the 0-5 cm soil layer than in the 5-20 cm soil layer in all treatments.3.Effect of chemical fertilizer with biochar on soil organic carbon fraction(1)In the 0-5 cm soil layer,compared with chemical fertilizer alone,chemical fertilizer with different amounts of biochar increased soil DOC,POC,MOC,ROC and CPMI,a rise of 0.84%～12.35%,88.03%～114.54%,26.45%～63.42%,29.79%～42.50%,and 22.50%～30.62%respectively.Compared with biochar alone,chemical fertilizer with different amounts of biochar increased soil MOC,ROC and CPMI,but decreased POC,and DOC did not increase significantly.In the 5-20 cm soil layer,compared with fertilizer alone,chemical fertilizer with different amounts of biochar significantly increased DOC,POC MOC,a rise of 29.66%～44.72%,190.75%～432.06%and 13.87%～57.18%,respectively;chemical fertilizer with medium and high amounts of biochar significantly increased ROC and CPMI,a rise of 27.80%,12.47%,and 39.25%,32.30%,respectively.Compared with biochar alone,chemical fertilizer with medium amount of biochar had no significant effect on DOC,MOC,and chemical fertilizer with high amount of biochar significantly increased ROC and CPMI.Two kinds of soil layers,chemical fertilizer with biochar reduced soil MB C compared with chemical fertilizer or biochar alone.(2)MBC,POC,MOC,and ROC all showed greater changes in 0-5 cm soil layer than 5-20 cm soil layer under chemical fertilizer with biochar treatment,but the changes in DOC content were reversed.In conclusion,chemical fertilizer with biochar improved rice yield and soil fertility to a certain extent,and chemical fertilizer with medium amount of biochar was the optimal application scheme to improve rice yield and soil fertility.