Physicochemical properties, total and DTPA （diethylenetriaminepentaacetic acid）-extractable Cu, Zn, Pb and Cd contents, microbial biomass carbon （C） content and the organic C mineralization rate of the soils in a ...Physicochemical properties, total and DTPA （diethylenetriaminepentaacetic acid）-extractable Cu, Zn, Pb and Cd contents, microbial biomass carbon （C） content and the organic C mineralization rate of the soils in a long-term trace metal-contaminated paddy region of Guangdong, China were determined to assess the sensitivity of microbial indices to moderately metal-contaminated paddy soils. The mean contents of total Cu, Zn, Pb and Cd were 251, 250, 171, and 2.4 mg kg^-1 respectively. DTPA-extractable metals were correlated positively and significantly with total metals, CEC, and organic C （except for DTPA-extractable Cd）, while they were negatively and highly significantly correlated with pH, totall Fe and Mn. Metal stress resulted in relatively low ratios of microbial biomass C to organic C and in remarkable inhibition of the microbial metabolic quotient and C mineralization rate, which eventually led to increases in soil organic C and C/N. Moreover, microbial respiratory activity showed a stronger correlation to DTPA-extractable metals than to total metal content. Likewise, in the acid paddy soils some “linked” microbial activity indices, such as metabolic quotient and ratios of basal respiration to organic C, especially during initial incubation, were found to be more sensitive indicators of soil trace metal contamination than microbial biomass C or basal respiration alone.展开更多
The soils in the South China Sea Islands (SCSI) were divided into three types, namely, phospho-calc soils,skeletisols and coastic solonchaks, which were derived from bio-clastic and strongly calcareous sediments. Inco...The soils in the South China Sea Islands (SCSI) were divided into three types, namely, phospho-calc soils,skeletisols and coastic solonchaks, which were derived from bio-clastic and strongly calcareous sediments. Incomparison with their parent materials, the phospho-calc soils have higher contents of P, Zn, Cu, Ba, and Cd,which tend to increase gradually with time, and lower contents of Mg, Ca, Sr, B, V, Pb, and Mo, which tendto decrease by degrees with time. The above-mentioned constitnents in skeletisols and coastic solonchaks aresimilar to those in their parent materials except for P and Na. The factors atfecting element distribution aremainly special bioclimate and parent material, meanwhile, resulting in the remarkable iulluence on elementdistribution through soil-forming time.展开更多
The land fallow policy was adopted by central and local governments to encourage the abandonment of water-intensive crops, such as winter wheat, in groundwater over-exploited areas. At the same time, since the 1990s, ...The land fallow policy was adopted by central and local governments to encourage the abandonment of water-intensive crops, such as winter wheat, in groundwater over-exploited areas. At the same time, since the 1990s, many households in the North China Plain （NCP） have chosen to replace the winter wheat and summer maize double-cropping system with the spring maize single-cropping system. Therefore, it is crucial to identify target land parcels for winter wheat abandonment and to design reasonable and proper standards for ecological compensation prior to the implementation of the land fallow policy in the NCP. In this study, multi-level Iogit models were used with household survey data in order to detect determinants across land parcel, household and village levels on household cropping system decisions; the opportunity costs for winter wheat abandonment were also calculated using cost-benefit analysis. The results show that： （1） land quality and irrigation condition at parcel level are two essential elements influencing household cropping system decisions. Nearly 70% of the total area of poor land and more than 90% of the total area of unirrigated land has suffered winter wheat abandonment. Target land parcels for the land fallow policy should be those that are irrigated and of high quality. （2） There were no significant differences between net profits from spring maize and summer maize under similar farming conditions, and the opportunity cost for winter wheat abandonment should be equal to the net profit of winter wheat. （3） The primary purpose of the land fallow policy is to induce groundwater recovery and restoration as a preliminary stage. A higher level of 350 yuan/mu is recommended as subsidy for ecological compensation at this stage. Later, the primary purpose of the policy should be a transition to a balance between exploitation and supplementation of water resources, and a lower level of 280 yuan/mu is recommended as a subsidy at this stage.展开更多
基金Project supported by the France-China. Advanced Research Programme, France (No. PRA E03-03) and Natural ScienceFoundation of Guangdong Province (No. 032255).
文摘Physicochemical properties, total and DTPA （diethylenetriaminepentaacetic acid）-extractable Cu, Zn, Pb and Cd contents, microbial biomass carbon （C） content and the organic C mineralization rate of the soils in a long-term trace metal-contaminated paddy region of Guangdong, China were determined to assess the sensitivity of microbial indices to moderately metal-contaminated paddy soils. The mean contents of total Cu, Zn, Pb and Cd were 251, 250, 171, and 2.4 mg kg^-1 respectively. DTPA-extractable metals were correlated positively and significantly with total metals, CEC, and organic C （except for DTPA-extractable Cd）, while they were negatively and highly significantly correlated with pH, totall Fe and Mn. Metal stress resulted in relatively low ratios of microbial biomass C to organic C and in remarkable inhibition of the microbial metabolic quotient and C mineralization rate, which eventually led to increases in soil organic C and C/N. Moreover, microbial respiratory activity showed a stronger correlation to DTPA-extractable metals than to total metal content. Likewise, in the acid paddy soils some “linked” microbial activity indices, such as metabolic quotient and ratios of basal respiration to organic C, especially during initial incubation, were found to be more sensitive indicators of soil trace metal contamination than microbial biomass C or basal respiration alone.
文摘The soils in the South China Sea Islands (SCSI) were divided into three types, namely, phospho-calc soils,skeletisols and coastic solonchaks, which were derived from bio-clastic and strongly calcareous sediments. Incomparison with their parent materials, the phospho-calc soils have higher contents of P, Zn, Cu, Ba, and Cd,which tend to increase gradually with time, and lower contents of Mg, Ca, Sr, B, V, Pb, and Mo, which tendto decrease by degrees with time. The above-mentioned constitnents in skeletisols and coastic solonchaks aresimilar to those in their parent materials except for P and Na. The factors atfecting element distribution aremainly special bioclimate and parent material, meanwhile, resulting in the remarkable iulluence on elementdistribution through soil-forming time.
基金National Natural Science Foundation of China,No.41571095,No.41271119
文摘The land fallow policy was adopted by central and local governments to encourage the abandonment of water-intensive crops, such as winter wheat, in groundwater over-exploited areas. At the same time, since the 1990s, many households in the North China Plain （NCP） have chosen to replace the winter wheat and summer maize double-cropping system with the spring maize single-cropping system. Therefore, it is crucial to identify target land parcels for winter wheat abandonment and to design reasonable and proper standards for ecological compensation prior to the implementation of the land fallow policy in the NCP. In this study, multi-level Iogit models were used with household survey data in order to detect determinants across land parcel, household and village levels on household cropping system decisions; the opportunity costs for winter wheat abandonment were also calculated using cost-benefit analysis. The results show that： （1） land quality and irrigation condition at parcel level are two essential elements influencing household cropping system decisions. Nearly 70% of the total area of poor land and more than 90% of the total area of unirrigated land has suffered winter wheat abandonment. Target land parcels for the land fallow policy should be those that are irrigated and of high quality. （2） There were no significant differences between net profits from spring maize and summer maize under similar farming conditions, and the opportunity cost for winter wheat abandonment should be equal to the net profit of winter wheat. （3） The primary purpose of the land fallow policy is to induce groundwater recovery and restoration as a preliminary stage. A higher level of 350 yuan/mu is recommended as subsidy for ecological compensation at this stage. Later, the primary purpose of the policy should be a transition to a balance between exploitation and supplementation of water resources, and a lower level of 280 yuan/mu is recommended as a subsidy at this stage.
