| Biocharapplication is considered as a potential way for sequestering carbon insoil,mitigatinggreenhouse gas emissions and improving soil quality. However, the actual effect ofbiochar amendment is attributed to several factors, such as the source and property of biochar, soil type,crops and fertilizer management. To date, there are still some uncertainties regarding the long-termresponses of soil carbon pools and crop yields to biochar amendment while the relevant study is limited.In this study, we investigated the effect of consecutivebiochar application for5years on soil carbonsequestration and grain yields in a high-yield farmland of north China. Soil respiration (RS) and soillabile organic carbon dynamics were monitored throughout the maize and wheat season(6/2012-6/2013). In addition, crop root respiration dynamics (6/2013-10/2013) and crop yields(2011-2013) were measured. The field experiment was established in2007, located inHuantaiAgroecosystem Experimental Station of China Agricultural University, Shandong province,where the winter wheat (Triticumaestivum L.: early October to mid-June) and summer maize (Zea maysL.: late June to late September) rotations are the typical cropping system.The experiment was carriedout with four treatments in randomly arranged plots. Three replications were conducted per treatment,four experiment treatments including: a control plot without biochar addition (CK), biocharincorporation at4.5t ha-1yr-1(BC4.5), biochar incorporationat9.0t ha-1yr-1(BC9.0), and incorporatedwheat straw (SR).Rswas determined using the Li-8100A (Li-Cor Company, USA) apparatus, soil temperature andmoisture at5cm depth were measured simultaneously. The soil microbial biomass carbon(MBC)contentwas measured by fumigation-extraction method, and the soil readily oxidized carbon (ROC)content was measured by dilute KMnO4oxidation method. Meanwhile, the soil hot-water extractablecarbon (HWC) content was measured by hot water (80°C)extraction method, and the soil black carbon(BC) content was measured by potassium dichromate oxidation method. The main results are asfollows:(1) The obvious diurnal and seasonal variations in Rs under all treatments were observed.Compared with the changes in Rs according to the summer maize season, the coefficient of variation(CV) was higher (48.4%~53.4%)than that of winter wheat season (with CV value ranging from65.1%to74.8%). There was no significant difference inthe values of CV between treatments. Overall, the soilrespiration cumulative emission of CK, BC4.5, BC9.0and SR was26.64,27.63,27.80,33.11t CO12ha-during the study period. Compared with CK, BC4.5and BC9.0had no significant effect on soilrespiration cumulative emission of winter wheat and summer maize（P>0.05）; SR significantlyincreased soil respiration cumulative emission of winter wheat（P<0.05）. BC4.5, BC9.0and SR had nosignificant effect oncrop root respiration cumulative emission of summer maize and the proportion ofmaize root respiration cumulative emission to soil respiration cumulative emission（P>0.05）.Rs rate presented a significant exponential relationship with soil temperature（P>0.05）.Q10insummer maize season(3.64-4.20) was higher than winter wheat season（2.60-3.17）for alltreatments. There was no significant difference between the treatments（P>0.05）during summer maizeseason, and the Q10for SR was significantly higher than other treatments in winter wheat season（P<0.05）.Extremely negative correlation was observed between soil moisture and RS（P<0.01）.(2) Compared with CK,the biochar treatments (BC4.5and BC9.0) significantly increased soil MBC and ROC contents（P<0.05), whereas had no significant effect on HWC content. SR significantlyincreased contents of MBC, ROC and HWC（P<0.05) relative to other three treatments. In addition, soilMBC, ROC and HWC contents showed large seasonal variations, where the CV for MBC (35.3-46.0%)was higher than that of ROC (27.4-24.9%) and HWC (17.8-29.2%). Among the BC4.5, BC9.0and SRtreatments, there was no significant effect on season fluctuation for MBC, but less fluctuation for ROCwas observed. On the other hand, SR increased season fluctuation for soil HWC significantly（P<0.05）,but the season fluctuation of soil HWC between BC4.5and BC9.0treatments was not significant.Additionally, biochar amendments significantly increased BC and soil organic carbon concentrations,the effect was enhanced with biochar application rate increased. Compared with CK, the content of BCwas increased by180%under BC4.5and337%under BC9.0, and the content of SOC was increased by19.7%under BC4.5and60.7%under BC9.0.(3) There was no significant difference in practical yieldorthe ear number of wheat and maizeamong different treatments. However, both the maize grain number per ear (6/2012-10/2012) and thewheat thousand seed weight (10/2012-6/2013) under BC9.0and SRwerehigher than that of CKtreatment.In summary, this study concluded that biochar did notsignificantly influence crop yields after5years consecutiveapplication. Under the high and stable crop yield condition, biochar applicationsignificantly increased soil organic carbonand black carbon content, but the effect on the soil respirationcumulative emission was not significant. Our study indicates that consecutive biochar application couldsignificantly increase soil carbon sequestration. |
PDF Full Text Request