| In order to investigate soil carbon and nitrogen dynamics during wheat and maize plantparts and straw biochar decomposition in soil, two incubation experiments were carried out toinvestigate the dynamics of soil labile carbon and nitrogen during decomposition of cropresidues (straw, root, stem and leaf). moreover, It was also investigated the effect of combinedadditions of wheat and maize straw with its biochar on soil total organic C, total N and activesoil organic C and N fractions in soil, and the sensitivity of labile soil carbon fractions forevaluating changes in soil organic matter, meanwhile, the soil coarse and fine particulateorganic carbon contents. The important results are as follows:1. In order to investigate labile carbon and nitrogen dynamics during maize plant partsdecomposition in straw-amended soil, an incubation experiment was carried out to study thedecomposition characteristics of an equal amount of maize residues (straw, root, stem and leaf)in straw-amended and unamended soils, the former soil was incorporated with straw and rootresidues together, the latter (control soil) with root residues only, obtained from aseven-season of summer maize and winter wheat continuous rotation system on GuanzhongPlain, Shaanxi province, China. Periodic measurement of soil microbial biomass carbon andnitrogen (SMBC, SMBN), dissolved organic carbon (DOC), mineral nitrogen was performedregularly over the62-day incubation. The results showed that soil labile carbon and nitrogenchanged rapidly in the first7days. Contents of SMBC and SMBN for the straw wassignificantly (P<0.05) higher than for the root, leaf addition was greater than obtained forstem addition during the first28d and14d, afterwards followed the opposite pattern, strawlied in between leaf and stem addition. The contents of DOC and mineral nitrogen slowed inthe order, leaf> straw> stem> root. At the end of the incubation, SMBC and mineralnitrogen contents increased significantly, DOC almost unchanged and SMBN declined acrossall residue treatments. Compared to the non-amended soil, straw-amended soil had nosignificant effect on decomposition of fresh residues, and the differences in soil labile Nbetween two soils were more significant than soil labile C. It is concluded that soil labile Cand N dynamics were influenced primarily by the content of chemical compositions such as Cand N of the added residues of the different organs. A same amount of straw is morefavorable for replenishing soil C and N compared to root after incorporated into soil, and the soil labile N was more sensitive than C to straw-amended soil.2. An80-day incubation study was carried out to investigate the effect of combinedadditions of wheat and maize straw with its biochar on soil total organic C, total N and activesoil organic C and N fractions in soil, and the sensitivity of labile soil carbon fractions forevaluating changes in soil organic matter. The results found that the cumulative mineralizationrate was18.3%when combined application of straw and biochar, which fall in between2.71%and45.0%with the single application. Soil total organic C, microbial biomass C,dissolved organic C and particulate organic C were averagely increased by22.9%,184%,23.6%and43.4%when addition of straw and biochar, in accordance with10.4%,102.6%,49.0%and7.4%under straw amendment as compared to control. Addition of straw togetherwith biochar increased soil mineral N and particulate organic N by5.8%and26.7%, whilereduced microbial biomass N by67.7%in comparison with only straw addition. Response oflabile soil carbon fractions were greatest found for biochar-amended soil, and microbialbiomass C, particulate organic C and mineralized carbon were the indicators most sensitive tochanges in SOM. It was suggested that combined application of straw with biochar more infavour of improving soil potential fertility and maintaining the season of fertilizer efficiencyby overcoming higher or lower mineralization rate while harmonizing advantages undersingle application. Soil microbial biomass C, particulate organic C and mineralized carboncan be used as sensitive indicators for detecting changes in SOM.3. Crop residues (fine straw and root) with straw biochar of the two main crops (wheatand maize) were used in a laboratory decomposition experiment. The objective were to assessthe decomposition dynamics of individual plant residues of varying quality and to examinethe effects of combined addition of straw and root with biochar on soil coarse and fineparticulate organic carbon contents. Residue-amended soil with the high soil cumulativeorganic carbon content and mineralization rate, residues with biochar combined inhabited themineralization of residue carbon. Compared to the control, addition of biochar aloneaveragely increased the soil organic carbon by35.5%, which was higher than12.6%and21.8%when residue amended individually or with biochar together. Fine particulate organiccarbon content and proportion were4.21~6.82g/kg and25.6%~33.4%greater than thecorresponding of corse particulate organic carbon1.08~1.51g/kg and6.43%~7.47%. Theobsvered value of particulate organic carbon content and proportion were all higher than thepredicted value. FPOC was the more sensitive indicator than CPOC and SOC. It wassuggested that fine and corse particulate organic C can be used as sensitive indicators fordetecting changes in soil organic matter. |
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