The Effects Of Biochar On Crop Growth,soil Fertility And Nutrients Use Efficiency Under Rapeseed-rice Rotation System

In the last 50 years,the farming practices of intensive use of inorganic fertilizers and chemicals are alarming for the depletion of soil fertility and sustainable agriculture.In addition,various adverse effects of these chemical fertilizers also negatively affect the environment,human population,and crop production.Therefore,it is crucial to adopt such environment-friendly fertilization strategies to reduce chemical fertilizers inputs,maintain high yield and ensure sustainable agriculture in the future.Previous studies have suggested various management strategies for chemical fertilizers,such as slow-release fertilizers,optimal levels of chemical fertilizers,and side-deep placement;however,these techniques are not economical due to high labor costs and lack of technology.In comparison,integrated field management and fertilization techniques such as crop rotation and biochar integration with chemical fertilizers seem more sustainable due to their positive role on the soil ecosystem,alleviating abiotic stresses,improving fertilizer and water use efficiency,and increasing crop production.Therefore,in current studies,the integral effects of biochar with inorganic fertilizers and crop rotation on soil and plant enzymatic activities,plant physiological traits,antioxidants,nutrients uptake by plants,yield contents,and post-harvest soil physiochemical properties were evaluated in greenhouse and field experiments.These investigations could propose a basis for sustainable cultivation of rice and rapeseed under integral application of biochar and inorganic fertilizer and crop rotation for higher and sustainable crop yields.The main results are summarized below.1.Effects of different nitrogen and biochar levels on seedlings growth and soil conditions in potted single-season rapeseedFirstly,a pot experiment was conducted to examine the integral effects of biochar and nitrogen over soil fertility,rapeseed seedling growth,and nitrogen utilization efficiency under the application of four nitrogen levels(0,75,225,and 450 kg ha^-1)and four biochar levels(0,5,10,and 15 t ha^-1).The results of this study showed that the integral application of biochar at 15 t ha^-1 and nitrogen at 450 kg ha^-1at 45 days after sowing（DAS）and 60 days after sowing（DAS）compensated the amount of nitrogen and increased total nitrogen accumulation（TNA）（93%and 62%）,leaf biomass（60%and33%）,stem biomass（20%and 22%）and photosynthesis（20%and 17%）at 45 DAS and60 DAS,respectively as compared to a single application of nitrogen.However,under the conditions of no nitrogen or 75 kg ha^-1 nitrogen application,the application of biochar to promote the growth of rapeseed plants was limited due to the less nitrogen supply.In contrast,the application of nitrogen at 450 kg ha^-1 and biochar at 5 or 10 t ha^-1showed that the growth of early seedlings was adversely affected due to high nitrogen concentration in soil.The present study’s findings imply that within the appropriate nitrogen application range of 225-450 kg ha^-1,the interaction of biochar and nitrogen might have an economical approach towards better utilization of nitrogen and sustainable crop production.2.Effects of different water conditions and biochar amounts on soil nutrients utilization,plant physiology,growth and yield in potted single-season rapeseedAnother pot experiment was carried out to evaluate the effect of biochar on photosynthesis,antioxidants activities,osmolytes contents,growth,and yield of rapeseed under drought stress.Rapeseed plants at the flowering stage were subjected to two moisture conditions,no stress（NS）and drought stress（DS）,along with four biochar treatments(B0:0,B15:15,B30:30,and B60:60 t ha^-1).The results showed that drought stress negatively affected rapeseed growth due to the over-production of hydrogen peroxide（H₂O₂）by increasing 45%,malondialdehyde（MDA）21%,and electrolyte leakage（EL%）40%in（B0+DS）treatment as compared to control（B0+NS）.However,the addition of biochar at 30 t ha^-1 alleviated the hostile effects of drought stress in rapeseed to reduce the contents of MDA,H₂O₂,EL by increasing the activities of superoxide dismutase（SOD）by 63%,peroxidase（POD）48%,and catalase（CAT）62%compared to stress-controlled treatment（B0+DS）.The amendment of biochar at 30 t ha^-1significantly increased rapeseed total biomass by 56%and 23%,pods plant^-1 by 26%and32%,seed weight plant^-1 by 56%and 208%,and 1000 grain weight by 15%and 21%,in well-watered conditions and drought conditions respectively as compared to control treatments of both water conditions.3.Integrated effects of different nitrogen and biochar levels on soil fertility,nitrogen use efficiency,plant physiology and yield in three seasons potted rapeseed-rice rotationA pot study of three seasons（two seasons rapeseed and one season rice）was conducted to investigate the long term effect of different biochar application levels(0,15,30,and 60 t ha^-1)applied once at the start of the experiment in combination with nitrogen fertilizer levels applied in each season,(0,75,225,and 450 kg ha^-1)for rapeseed and(0,150,300,and 450 kg ha^-1)for rice,on soil properties,rapeseed and rice growth,and nitrogen use efficiency.In the first season of rapeseed,biochar application significantly increased SOC by 359%in treatment B60+N225,NO₃^-by 198%in B30+N450,NH₄⁺by134%in B60+N450 and nitrogen use efficiency（NUE）by 40%in B15+N225.In the second season under the rice cultivation,SOC significantly increased by 417%in B60+N0,NO₃^-by 172%in B60+N450,NH₄⁺by 139%in B30+N450 and NUE by 59%in B30+N300.Similarly,in third season under rapeseed cultivation,SOC elevated by 308%in B60+N450,NO₃^-by 139%in B30+N450,NH₄⁺by 159%in B30+N450 and NUE by40%in B15+N225 treatment.The addition of high nitrogen B0+N450 compared to B0+N225 significantly reduced rapeseed plant height up to 3%and 5%,pods plant^-1 7%and 6%,and grain yield plant^-1 8%and 17%respectively during the first and second year.However,the ameliorative role of biochar at 30 t ha^-1 coupled with nitrogen at 450 kg ha^-1increased the rapeseed plant height up to 11%and 18%,pods plant^-1 39%and 32%and grain yield plant^-1 54%and 64%respectively during the first and second year.Compared to B0+N450,the combination of B30+N450 significantly increased the activities of nitrate reductase NR by 26%and 29%,nitrite reductase NIR 28%and 23%,glutamate synthase GS 97%and 89%,and glutamine synthetase GOGAT 28%and 87%in the first year and NR by 28%,and 33%,NIR 34%and 30%,GS 77%and 86%,GOGAT 74%and71%in the second year respectively at seedling stage（SS）and flowering stage（FS）of rapeseed.The results showed that a single application of 450 kg N ha^-1（N450）adversely affected the rice physiological and yield traits by destroying rice leaf ultrastructure and reducing the stomatal length by 13%,stomatal width 3%and density 12%,plant height5%,dry biomass plant^-1 4%,spike weight plant^-1 8%,and grain weight plant^-1 9%compared to N300 unless it was treated in combination with biochar.Compared to a single application of N450(450 kg N ha^-1),combined application of biochar and nitrogen（B30+N450）could elevate rice plant nitrogen content by 13%,plant height 30%,above-ground dry biomass plant^-1 136%,spike weight plant^-1 34%,and grain weight plant^-1 36%.4.Effects of different amounts of biochar on soil physiochemical properties and plant growth under field cultivations of three years（six seasons）under rice-rapeseed rotationA three-year field trial of rice-rape rotation was conducted to evaluate the long-term effects of biochar(0,3,9,15,30,and 60 t ha^-1)coupled with compound fertilizer NPK（15-15-15）at the（N:P:K ratio in rice and rapeseed were 1:0.8:0.8 and 1:0.5:0.5respectively）.The results showed that amendment of biochar at 60 t ha^-1 during rice cultivation seasons caused significant increases in contents of soil total nitrogen（TN）by16%,20%,and 22%,total phosphorus（TP）by 69%,72%,and 67%,and available potassium（AK）by 88%,190%and 88%in 2018,2019 and 2020 respectively as compared to control treatment.Similarly,the incorporation of biochar at 60 t ha^-1 also caused variable changes in soil macronutrients by increasing soil TN by 17%,19%,and23%TP by 60%,63%,and 67%,and AK by 96%,95%,and 97%respectively in three consistent years during rapeseed cultivation.The findings revealed that compared to control,plots treated with biochar at 30 t ha^-1 increased the activity of urease up to 52%and 39%and invertase by 15%and 32%,while biochar 60 t ha^-1 increased the activity of soil catalase by 34%and 32%and alkaline phosphatase by 35%and 41%respectively under rice and rapeseed cultivation in the last two years of the study.The results of the study showed that coupling of biochar 15 t ha^-1 with compound fertilizer significantly improved the grain yield of rice by 12%and rapeseed by 22%in the first year and biochar amendment at 30 t ha^-1 improved rice yield up to 14%and 22%and rapeseed up to18%and 21%in the last two years.However,60 t ha^-1 biochar was ineffective and reduced the nutrients uptake and yield throughout the study.The soil conditions,growth,and yield of rice and rapeseed were improved in control plots with no biochar in the last two years,indicating crop rotation’s positive effect.Altogether,our findings suggest that crop rotation under the combined application of biochar and chemical fertilizer is a promising approach to ensure soil fertility and crop productivity on a long-term sustainable basis.In summary,under the condition of rice-rape rotation,the use of biochar 15-30 t ha-1is beneficial to nutrient utilization and plant growth within 1-3 years,while the application of 60 t ha-1 in the initial stage will have a negative impact on crop nutrient absorption due to high carbon content;however,after three years the plant growth will improve as compared to control.Therefore,the integrated application of biochar and inorganic fertilizers had sustainable positive effects on soil conditions,nutrients uptake and utilization,and yield contents of rice and rapeseed.Furthermore,biochar addition significantly alleviated the adverse effects of drought stress and high nitrogen application by improving leaf ultrastructural and physiological traits.Moreover,biochar at 15 t ha^-1can also offset the deficiency of lower nitrogen as B15+N225 resulted in the highest NUE of 29%in both years.Altogether,our findings suggest that biochar integration with chemical fertilizer could be an efficient approach for soil fertility improvement and higher crop yields on a long-term sustainable basis.