Effects And Mechanism Of Biochar Combined With Chemical Fertilizer On Plant Growth And Nitrogen Utilization In Rice

The management of nitrogen has now been identified as an imperative dimension for handling the global climate change and soil biology.Biochar(BC)is considered to be a climate change mitigation tool that can enhance N uptake and utilization in N-fertilized crops.However,there is limited information on changes cause by nitrogen(N)fertilizers and biochar(BC)application in soil carbon and nitrogen availability in paddy soil.By monitoring fertilizer nitrogen dynamics,a first comprehensive,pot cultivation experiment in early and late seasons during2019 was conducted to elucidate how different nitrogen fertilizer(¹⁵N-urea,¹⁵N-ammonium nitrate,and ¹⁵N-ammonium sulfate)with and without biochar alter the ability of paddy soil to store and cycle these nutrients.The experiment included six treatments:T1(¹⁵N-urea 315 kg N ha^-1),T2(¹⁵N-urea 315 kg N ha^-1+biochar 30 t ha^-1),T3(¹⁵N-ammonium nitrate 315 kg N ha^-1),T4(¹⁵N-ammonium nitrate 315 kg N ha^-1+biochar 30 t ha^-1),T5(¹⁵N-ammonium sulfate 315 kg N ha^-1)and T6(¹⁵N-ammonium sulfate 315 kg N ha^-1+biochar 30 t ha^-1)and the findings were divided in to three parts,i.e.,(1)To study the changes caused in carbon and nitrogen pools,microbial and enzymatic activities as a result of biochar addition,(2)To investigate the fate and efficacy of different N source applied with and without biochar and(3)To find out the effect of biochar application with nitrogen fertilizers on different morpho-physiological traits,leaf nitrogen concentration and nitrogen metabolism enzymes.Results documented(1)illustrated that all N fertilizers sources applied with biochar significantly increased soil organic carbon(SOC)content by an average48.44%and 50.63%,soil total nitrogen(Nt)by 4.56%and 4.94%,reduction in total nitrogen leaching by 42.63%and 76.16%,while dissolved organic carbon leaching(DOC)augmented by 39.87%and 38.38%than non-applied treatments in early and late season,respectively.Similarly,BC applied with N fertilizers,facilitated soil N transformation and the net concentration of NH₄⁺–N and NO₃^-–N were relatively higher than non-charred treatments.Moreover,in both early and late seasons,soil urease enzyme activity increased by an average 13.52%and13.55%,?-glucosidase by 15.99%and 19.27%however,catalase activity decreased by 14.58%and 12.38%,correspondingly.(2)Tracing fate of fertilizers revealed that ¹⁵N leaching was significantly reduced by 75.69%and 110.32%in BC vs.non-BC treatments across growth stages in the early and late seasons.The rate of leaching was lower for urea than for ammonium nitrate and ammonium sulfate.Furthermore,the addition of BC resulted in 55.58%and 41.33%higher soil ¹⁵N concentrations in the early and late season,respectively,indicating that BC increased N adsorption.N uptake by roots,stems,leaves,panicles,and grains averaged 52.39%,37.14%,40.86%,36.37%,and 29.94%higher in BC-amended pots than in BC-free pots in both seasons.There were significant differences(P<0.05)among N sources in terms of fertilizer N loss,residual N,and N uptake,and performance was ranked in the order urea>ammonium sulfate>ammonium nitrate.Results shown(3),that biochar integrated with N fertilizers significantly enhanced soil chemical properties compared with N fertilizers alone(P<0.05).Correlation analysis showed that rice root morphological traits were strongly related to soil chemical properties,and higher root growth was measured in the biochar treatments.The net leaf photosynthetic rate averaged 9.34%higher,chlorophyll(Chl)a concentration 12.91%higher,and Chl b concentration 10.05%higher in the biochar treatments than in the biochar-free treatments across the seasons.Notably,leaf ¹⁵N concentration was 23.19%higher in the biochar treatments in both seasons.These results illustrated the strong linkage between N concentration and the activities of N metabolism enzymes such as NR,GS,and GOGAT,all of which were higher in the biochar treatments.On the basis of results compiled from pot experiment 2019 in terms of fertilizers utilization and retention(urea>ammonium sulfate>ammonium nitrate with single dose of biochar).The field trials were conducted in early and late season of 2020 to evaluate the effect of high and low dose urea application with and without different rates of biochar on selected soil chemical properties,enzymatic activity,abundance of ammonia oxidizing bacteria(AOB),archaea(AOA),nitrite oxidizing bacteria(NOB),plant nitrogen uptake and grain yield.The treatments combination were(T1)N1B0(135 kg N ha^-1+0 t BC ha^-1),(T2)N1B1(135 kg N ha^-1+10 t BC ha^-1),(T3)N1B2(135 kg N ha^-1+20 t BC ha^-1),(T4)N1B3(135 kg N ha^-1+30 t BC ha^-1),(T5)N2B0(180 kg N ha^-1+0 t BC ha^-1),(T6)N2B1(180 kg N ha^-1+10 t BC ha^-1),(T7)N2B2(180 kg N ha^-1+20 t BC ha^-1),and(T8)N2B3(180 kg N ha^-1+30 t BC ha^-1).The findings recorded during field trials are as following;(1)The pH,the soil organic carbon(SOC)content,the total nitrogen(Nt)content,and mineral nitrogen content(NH₄⁺–N and NO₃^-–N),in the biochar-amended soil were higher compared to the control soil.The soil in the BC 20 t ha^-1(10.54 mg kg^-1)and BC 30 t ha^-1(10.25 mg kg^-1)treatments was characterized by the highest content of NO₃^––N,whereas the lowest nitrate nitrogen content was found in the only N fertilizer treatments N1BC0(8.95 mg kg^-1)and N2BC0(9.39mg kg^-1),across the seasons.(2)Biochar application combined with N fertilizer increased soil enzymatic activity.Phenol oxidase and dehydrogenase activity increased with increasing biochar rate.As far as urease,catalase and chitinase activity is concerned,a similar relationship was not recorded.In this case,the soil amended with biochar urease activity was found higher by an average 25.28%,phenol oxidase activity by14.13%,dehydrogenase activity by 67.76%,chitinase activity by 22.26%,whereas soil catalase activity was lower by 15.06%than soil applied with sole urea treatments.(3)Moreover,results illustrated that AOB abundance was significantly affected with biochar application,however no significant difference was recorded in case of AOA,and NOB abundance.The abundance of AOB was higher by an average 48%in biochar applied treatments compared with only non-applied treatments.(4)Additionally,the accumulation of nitrogen and grain yield was significantly higher in biochar applied treatments,and maximum uptake of nitrogen by stem,leaves and panicles in both early and late seasons were occurred in treatments applied with BC 20 and 30 t ha^-1.The nitrogen concentration in stem,leaves and panicles was higher by an average 24.46%,20.47%and 19.08%in biochar applied treatments than only N fertilizer application,respectively.The results of field trials revealed that biochar addition at the rate 20 or 30 t ha^-1 with low dose urea(135 kg N ha^-1)can be utilized in improving the soil nutrient status,soil biological functions,plant N uptake and rice grain yield.