准确预测未采样区域SOC密度,是研究SOC演变趋势和探索土壤固碳作用对缓解全球气候变化的基础。采用泛克里格法(Universal Kriging,UK)和土壤类型法(pedological professional knowledge-based method,PKB),分别对长兴县水稻土有机碳密度进行了预测,其中,UK直接以长兴水稻土剖面资料为源数据、PKB以长兴水稻土剖面数据和长兴1∶5万数字土壤图为源数据进行预测。根据平均绝对误差(MAE)及均方根误差(RMSE)大小,评价了两种方法在县域尺度土壤有机碳密度空间预测效果。结果表明:UK的MAE(31.2)、RMSE(52.5)均大于PKB的MAE(24.7)、RMSE(43.1),说明PKB法的预测效果较好,UK法相对较差。研究表明,对土壤类型、土壤母质,以及剖面点位置等信息的综合考虑能使PKB法更好地表达土壤属性的空间特征,也更适于县域尺度土壤有机碳密度的空间预测。
The agricultural soil carbon pool plays an important role in mitigating greenhouse gas emission ana unaerstanamg the son orgamc carbon-climate-soil texture relationship is of great significance for estimating cropland soil carbon pool responses to climate change. Using data from 900 soil profiles, obtained from the Second National Soil Survey of China, we investigated the soil organic carbon （SOC） depth distribution in relation to climate and soil texture under various climate regimes of the cold northeast region （NER） and the warmer Huang-Huai-Hai region （HHHR） of China. The results demonstrated that the SOC content was higher in NER than in HHHR. For both regions, the SOC content at all soil depths had significant negative relationships with mean annual temperature （MAT）, but was related to mean annual precipitation （MAP） just at the surface 0-20 cm. The climate effect on SOC content was more pronounced in NER than in HHHR. Regional differences in the effect of soil texture on SOC content were not found. However, the dominant texture factors were different. The effect of sand content on SOC was more pronounced than that of clay content in NER. Conversely, the effect of clay on SOC was more pronounced than sand in HHHR. Climate and soil texture jointly explained the greatest SOC variability of 49.0% （0-20 cm） and 33.5% （20-30 cm） in NER and HHHR, respectively. Moreover, regional differences occurred in the importance of climate vs. soil texture in explaining SOC variability. In NER, the SOC content of the shallow layers （0-30 cm） was mainly determined by climate factor, specifically MAT, but the SOC content of the deeper soil layers （30-100 cm） was more affected by texture factor, specifically sand content. In HHHR, all the SOC variability in all soil layers was predominantly best explained by clay content. Therefore, when temperature was colder, the climate effect became stronger and this trend was restricted by soil depth. The regional differences and soil depth influence un
WANG Mei-YanSHI Xue-ZhengYU Dong-ShengXU Sheng-XiangTAN Man-ZhiSUN Wei-XiaZHAO Yong-Cun
Changes in soil organic carbon (SOC) in agricultural soils influence soil quality and greenhouse gas concentrations in the atmosphere. Dry farmland covers more than 70% of the whole cropland area in China and plays an important role in mitigating carbon dioxide (CO2) emissions. In this study, 4109 dry farmland soil polygons were extracted using spatial overlay analysis of the soil layer (1:500000) and the land use layer (1:500000) to support Century model simulations of SOC dynamics for dry farmland in Anhui Province, East China from 1980 to 2008. Considering two field-validation sites, the Century model performed relatively well in modeling SOC dynamics for dry farmland in the province. The simulated results showed that the area-weighted mean soil organic carbon density (SOCD) of dry farmland increased from 18.77 Mg C ha1 in 1980 to 23.99 Mg C ha1 in 2008 with an average sequestration rate of 0.18 Mg C ha1 year?1. Approximately 94.9% of the total dry farmland area sequestered carbon while 5.1% had carbon lost. Over the past 29 years, the net SOC gain in dry farmland soils of the province was 19.37 Tg, with an average sequestration rate of 0.67 Tg C year1. Augmentation of SOC was primarily due to increased consumption of nitrogen fertilizer and farmyard manure. Moreover, SOC dynamics were highly differentiated among dry farmland soil groups. The integration of the Century model with a fine-scale soil database approach could be conveniently utilized as a tool for the accurate simulation of SOC dynamics at the regional scale.
WANG Shi-HangSHI Xue-ZhengZHAO Yong-CunD. C. WEINDORFYU Dong-ShengXU Sheng-XiangTAN Man-ZhiSUN Wei-Xia
Organochlorinated compounds are ubiquitous contaminants in the environment, especially in industrial sites. The objective of the work was to investigate whether a vegetable field near an industrial site is safe for vegetable production. The residues of chlorobenzenes （CBs）, hexachlorocyclohexanes （HCHs） and dichlorodiphenyltrichloroethanes （DDTs） in a vegetable field which was near a chemical plant in China were characterized. Point estimate quotient was used for ecological risk assessment of the investigated site. The results showed that all CBs except monochlorobenzene （MCB） were detected in soils. The total concentrations of ∑ CBs ranged from 71.06 to 716.57 ng/g, with a mean concentration of 434.93 ng/g. The main components of CBs in soil samples were dichlorobenzenes （DCBs）, trichlorobenzenes （TCBs） and tetrachlorobenzenes （TeCBs）, while for single congeners, 1,2,4-TCB had the highest concentration, which ranged from 13.21 to 210.35 ng/g with a mean concentration of 111.89 ng/g. Residues of hexachlorobenzene （HCB） in soil samples ranged from 0.9 to 11.79 ng/g, significantly lower than ∑ DCB, ∑ TCB and ∑ TeCB. Concentrations of ∑ HCHs and ∑ DDTs in soils ranged from 11.32 to 55.24 ng/g and from 195.63 to 465.58 ng/g, respectively, of which the main components were α-HCH and p,p＇-dichlorodiphenyldichloroethylene （p,p＇-DDE）. Ecological risk assessment for the investigated site showed that the most potential risks were from TCBs and TeCBs, based on the hazard quotients. The higher residues of CBs and DDTs compared to the target values and the higher than 1 hazard quotients indicated that this area is not safe for vegetable production and thus soil remediation is needed.
Yang SongFang WangYongrong BianYinping ZhangXin Jiang
