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Carbon stable isotope techniques were extensively employed to trace the dynamics of soil organic carbon (SOC) across a land-use change involving a shift to vegetation with different photosynthetic pathways. Based on the isotopic mass balance equation, relative contributions of new versus old SOC, and SOC turnover rate in corn fields were evaluated world-wide. However, most previous research had not analyzed corn debris left in the field, instead using an average corn plant δ 13C value or a measured value to calculate the proportion of corn-derived SOC, either of which could bias results. This paper carried out a detailed analysis of isotopic fractionation in corn plants and deduced the maximum possible bias of SOC dynamics study. The results show approximately 3‰ isotopic fractionation from top to bottom of the corn leaf. The 13C enrichment sequence in corn plant was tassel > stalk or cob > root > leaves. Individual parts accounting for the total dry mass of corn returned distinct values. Consequently, the average δ 13C value of corn does not represent the actual isotopic composition of corn debris. Furthermore, we deduced that the greater the fractionation in corn plant, the greater the possible bias. To alleviate bias of SOC dynamics study, we suggest two measures: analyze isotopic compositions and proportions of each part of the corn and determine which parts of the corn plant are left in the field and incorporated into SOC.

Corrosion mechanism of automotive mufflers was investigated by SEM (scanning electron microscope) and XRD (X-ray diffractomer) analysis. 409L and newly developed 439M steels were evaluated in terms of condensate corrosion tests for 5 periods, 10 periods and 20 periods separately. The relative lifetimes of 409L and 439M steels were predicted according to the extreme value analysis method and pitting corrosion models. Modelling studies demonstrated that the predicted relative lifetime of 439M ferrite stainless steel is 6. 8 times that of 409L steels. The extreme value analysis method was also successfully used in the road test. The estimated maximum corrosion depth of the 439M muffler is 0. 55 mm.

The properties of soils derived from carbonate rock, red residua, and sand-shale in Guizhou province, China are essentially different. However, the effects of parent material and anthropogenic activities on the concentration of trace elements when the soils are converted into paddy soils are unknown. A total of 319 paddy topsoil samples (0–20 cm) were collected in a typical region to determine their relative contribution to the concentrations of trace elements in the soil. The results indicated that the contents of trace elements were far beyond the uncultivated soil background and the input of organic fertilizers was presumably responsible for accumulation of trace elements. In addition, principal component analysis showed that the first component included Cd, Cr, and As, which strongly associated with anthropogenic activities. Pb and Hg formed the second component, which related to both parent materials and anthropogenic input. Furthermore, the Cr and Hg contents in paddy soil derived from carbonate rock have higher values than other types of soils partly because of the high background values as well as slightly alkaline condition. In the paddy soil derived from red residua, high physical clay content accounted for enrichment of Pb.

For establishing rational farming mechanism, it is essential to know the relative contribution of different geological background and anthropogenic activities to trace elements in agricultural soil. In this paper, 282 surface soil samples were collected based on the different geological background. Five harmful trace elements (As, Cd, Cr, Hg and Pb) were analyzed. The results indicated most of trace elements contents were far beyond the threshold of uncultivated soil background, which indicate anthropogenic input strongly influenced on trace elements in agricultural soil. In addition, correlation analysis showed trace element contents exhibited high relationships with soil pH, C/N and physical clay (

There is considerable discussion and uncertainty in the literature regarding the importance of fresh litter versus older soil organic matter as sources of soil dissolved organic carbon (DOC) in forest floor. In this study, the differences of organic carbon concentration and stable isotope composition were analyzed under different background conditions to identify the origins of DOC in forest soil. The data show that there is no significant difference in SOC content between these collected soil samples (P > 0.05), but the litter-rich surface soils have relatively higher DOC concentration than the litter-lacking (P