[Remediation Effect and Mechanism of Biochar in Combination with Nitrogen Fertilizer on Cd-contaminated Paddy Soil].

Cadmium (Cd) heavy metal pollution has posed serious threats to soil health and the safe production utilization of agricultural products. A pot experiment was conducted to study the effects of biochar (BC) and nitrogen fertilizer with three levels, namely 2.6 g·pot-1 (N1), 3.5 g·pot-1 (N2), 4.4 g·pot-1 (N3) biochar combined with nitrogen fertilizer (BCN1, BCN2, and BCN3), on soil Cd fractions, Cd enrichment, the transport of rice, and soil enzyme activity, as well as the changes in microbial community composition and complex interactions between microorganisms through high-throughput sequencing. The results showed that biochar combined with nitrogen fertilizer led to the transformation of Cd from the exchangeable state to the residue state, and the proportion of the exchangeable state was significantly reduced by 6.2%-14.7%; by contrast, the proportion of the residue state increased by 18.6%-26.4% relative to that in CK. In addition, singular treatments of nitrogen fertilizer enhanced the accumulation capacities of Cd in roots, which increased by 22%-33.5% compared with that in CK. By contrast, the BC and BCN treatments reduced Cd accumulation in roots and the transfer capacity from stems to rice husks and husk to rice. Furthermore, the BCN treatments promoted soil enzyme activities (urease, acid phosphatase, invertase, and catalase). MiSeq sequencing showed that BCN treatments increased the abundance of the main species of soil bacterial microbes (such as Acidobacteriales, Solibacterales, Pedosphaerales, and Nitrospirales). Moreover, co-occurrence network analysis showed that the complexity of the soil bacterial network was enhanced under the N, BC, and BCN treatments. Overall, biochar combined with nitrogen fertilizer reduced soil Cd availability, inhibited the capacity of Cd accumulation and the transport of rice, and improved the soil eco-environmental quality. Thus, using BCN could be a feasible practice for the remediation of Cd-polluted agricultural soil.

[Technological Classification of Cadmium Quality in the Rice Producing Areas of South China].

Classifying the quality of agricultural products is an important means of managing the arable land quality and guaranteeing the quality and safety of agricultural products. This work is planned to be completed in 2020. However, there is still no perfect method or technology for classifying the quality of arable lands. The species sensitivity distribution (SSD) has become commonly used for determining ecological safety thresholds since it takes into account differences in species sensitivity, the physical and chemical properties of soils, biological availability, and sources of pollutants. However, it has not yet been applied to the classification of arable land quality. Therefore, based on the routine monitoring data of rice production areas in southern China from the Agro-environmental Monitoring Center of China, this study proposes the use of species sensitivity distributions to classify the environmental quality of cadmium in rice production areas. The scientific rationale of this method was also discussed in order to provide an important reference for the construction and improvement of the classification system for arable land quality in China. The results showed that the pH, soil organic matter, and cation exchange capacity of the physical and chemical properties of soils significantly affected the enrichment of cadmium in rice, and this relationship was used to establish the cadmium transfer equation in the soil-rice system. It was found that there were obvious differences in the cadmium enrichment abilities of different rice varieties, which were mainly caused by the differences in their genotypes. According to the species sensitivity distributions, soil cadmium thresholds were obtained, which yielded a priority protection class of less than 0.26 mg·kg-1 and strict control class of greater than 1.67 mg·kg-1, between which are the safe use classes. The results were verified through independent datasets, and it was found that the application of species sensitivity distributions to classify the environmental quality of cadmium in rice producing areas reflected good scientific rationale and operability. This study may provide a foundation for the construction and improvement of the arable land quality classification system in China.

[Adsorption of Cd2+ on biochar from aqueous solution].

Biomass-based materials such as biochar have a good performance in heavy metal adsorption. The adsorption of Cd2+ on biochar converted from cotton straw was studied. Adsorption isotherm, kinetics and effect factors such as temperature, pH and ionic strength were investigated. The adsorption of Cd2+ on biochar can be fitted by the Freundlich isotherm better than the Langmuir isotherm. The maximum adsorption amounts of Cd2+ at different temperatures were 9.738 mg x g(-1) (288.15 K), 10.14 mg x g(-1) (298.15 K), 10.40 mg x g(-1) (308.15 K) and 10.71 mg x g(-1) (318.15 K), respectively. The free energies AG(theta) were from -8.346 kJ x mol(-1) to -10.276 kJ x mol(-1) at different temperatures, indicating that the adsorption of Cd2+ onto biochar is spontaneous and is an endothermic process. The adsorption process can reach equilibrium within 40 minutes and can be fitted by the pseudo second order kinetic model. pH showed a significant effect on the adsorption of Cd2+ on biochar in the range of 2-8. The adsorption amount of Cd2+ on biochar shows a reducing trend with the increasing ionic strength.