水溶性磷肥在施入土壤后容易被固定,通常当季磷肥利用率仅为 10%～25%.磷肥的持续大量施用,使得磷在耕地中积累的环境风险持续升高.基于此,本文结合国内外研究现状,综述了土壤磷素累积的现状及危害,总结了土壤磷素的分级形态、固定机制和高效利用技术.在此基础上,对今后的研究工作进行了展望,以期为农业可持续发展提供理论依据和实践方法.

水稻是一种富集重金属能力极强的农作物之一.随着现代工业的不断发展,我国大米镉污染问题日益严重.本文结合现有研究,研判了大米镉污染现状及危害,总结了影响镉大米生物有效性的关键因素和大米镉污染控制技术,以期为农业可持续发展提供理论依据.

Cadmium (Cd) pollution and phosphorus (P) leaching in paddy soils has raised the global concern. In this study, two kinds of the low grade phosphate rocks activated by the sodium lignosulfonate (SL) and humic acid (HA) were fabricated for soil Cd passivation and reduction of the soil P leaching simultaneously. The mechanisms of the Cd adsorption and passivation by the activated phosphate rocks (APRs) were investigated through the batch experiment and the indoor culture test (i.e., incubation and pot experiments) in the Cd-polluted paddy soil. The effects of the APRs on the potted rice growth, uptake of Cd by rice and P loss were also studied. In comparison with the superphosphate treatment, the cumulative P loss from SL- and HA-APRs were reduced by the 65.2% and 65.3%. In terms of the Cd passivation, the Cd adsorbed on the APRs was through the chemical ways (i.e., ligand exchange and the formation of internal complexes). The application of the APRs significantly decreased the soil exchangeable Cd by 48.9%–55.0%, while the Fe/Mn oxides-bound Cd and residual Cd increased significantly by 19.6%–20.3% and 50.7%–69.4%, respectively. Pot experiment also suggested that both the APRs treatments (SL- and HA-APRs) significantly diminished soil Cd accumulation in rice (by 72.7% and 62.8%) coupling with the significantly decreased P leaching. These results provide a sustainable way to explore a novel cost-effective, high-efficient and bi-functional mineral-based soil amendments for environmental remediation.

Phosphorus (P) build-up in agricultural soils as a consequence of excessive P fertilizer application necessitates the exploration of soil P pool for crop supply. We conducted a soil incubation experiment, pot experiments, and field experiments to study the effects of different P activators (Pas) (humic acid, lignosulfonate sodium, and biochemical humic acid) on soil phosphate fraction, rice yield, and P loss. Through chemical analyses and microbial community structure measurement, we found that Pas significantly increased paddy soil water-soluble P (WSP), available P, Fe-P, and relative abundances of P-mineralizing and P-solubilizing microorganisms, whereas they decreased Al-P and microbial alpha diversity. Our pot experiment results showed that the application of Pas significantly reduced soil P loss and resulted in grain yield comparable to those obtained by fertilization with P fertilizers, and significantly higher than those in the control plants. The results of the field experiment suggested that Pas are able to increase rice yield more significantly than P fertilizers and improve the P utilization efficiency of rice plants. We conclude that application of Pas was more effective in reducing P leaching, soil total P, WSP, and Olsen P than P fertilizers during rice harvest.

Excessive cadmium (Cd) in rice grain has become a major global public health problem. Here, the effect of foliar glycerol application on Cd accumulation in brown rice was examined. Various spraying concentrations of glycerol between 0.4mM and 50mM were investigated and the results showed that 0.8 mM was the best application concentration for decreasing Cd content in brown rice. After different application period experiment, filling stage was considered as the optimal spraying time. 0.4mM-5mM glycerol application one time at the filling stage could significantly reduce Cd concentration in brown rice by 28.5%-60.4%. Cd transport factors (the ratio of brown rice and flag leaf/node) were decreased by 48.5% and 27.3%, respectively, with glycerol application. Glycerol application also significantly increased Cd concentration in soluble fraction in flag leaf while reduced inorganic Cd and water-soluble Cd in both flag leaf and stem. Our results showed foliar spraying glycerol inhibited Cd transport to brown rice through Cd compartmentalisation in the vacuole and transformation of cadmium chemical form. This study may provide a new method to effectively alleviate the problem of excessive Cd in rice. (C) 2020 Elsevier Ltd. All rights reserved.

At present, there are few reports on the profiling mechanism that can achieve surface envelope profiling along the surface of a shaft whose radius is constantly changing. Existing profiling mechanisms cannot achieve this function. To this end, a novel deployable arc profiling mechanism is presented in this paper. The mechanism can realize centering deployment along the shaft with a changing radius. The radius of the deployable arc can be adapted to the continuous change of shaft radius, and its surface can always maintain the arc shape for surface envelope profiling. The mechanism is mainly composed of compound cams. Each cam contains multiple grooves, and each groove connects to an arc support linkage. The arc support linkage is controlled by the compound motion of cams in different layers. The pitch curve of each groove is designed by applying the method of relative motion and inverse solution and obtained various parameter equations of the mechanism. The feasibility of this mechanism is verified by analysis, experiment, and application test. The results show that the proposed deployable arc profiling mechanism can achieve the design purpose and the profiling accuracy is kept above 96.425%.

Banana stem gripper is an important component of banana harvesting robot. Since banana bunches is heavy, and easy to slide and fall during robot harvesting, we should figure out the clamping safety margin of banana stem gripper for reliability manipulation. The clamping safety margin is the ratio of maximum load-bearing capability to object’s weight under given applied clamping force. It is able to evaluate special gripper’s clamping ability and useful for optimizing robot gripper’s structure parameters. A test platform is designed and fabricated for studying banana stem clamping safety margin. It consists of a rack, two cylinders, a straight-line moving mechanism, two clamping bases, etc. Different types of clamping part and clamping forces are tested and compared to evaluate their clamping safety margins. Compared to profile clamping part, the destructive puncture is more suitable for clamping and spends lower clamping force. Also, the relationship between the safety margin and clamping force are given, which is significant for selecting the proper clamping force of banana stem robot grippers.