总结了近年来在全国粮食主产区进行的1 333个田间试验结果,分析了目前条件下中国主要粮食作物水稻、小麦和玉米氮磷钾肥的偏生产力、农学效率、肥料利用率和生理利用率等,发现水稻、小麦和玉米的氮肥农学效率分别为10.4 kg kg-1、8.0 kg...总结了近年来在全国粮食主产区进行的1 333个田间试验结果,分析了目前条件下中国主要粮食作物水稻、小麦和玉米氮磷钾肥的偏生产力、农学效率、肥料利用率和生理利用率等,发现水稻、小麦和玉米的氮肥农学效率分别为10.4 kg kg-1、8.0 kg kg-1和9.8 kg kg-1,氮肥利用率分别为28.3%、28.2%和26.1%,远低于国际水平,与20世纪80年代相比呈下降趋势。造成肥料利用率低的主要原因包括高产农田过量施肥,忽视土壤和环境养分的利用,作物产量潜力未得到充分发挥以及养分损失未能得到有效阻控等。要大幅度提高肥料利用率就必须从植物营养学、土壤学、农学等多学科联合攻关入手,充分利用来自土壤和环境的养分资源,实现根层养分供应与高产作物需求在数量上匹配、时间上同步、空间上一致,同时提高作物产量和养分利用效率,协调作物高产与环境保护。展开更多
The origin and classification of soil enzymes are summarized in this paper. The foregone research results discover the close relationship between soil enzyme activity and soil quality (including soil chemical, physica...The origin and classification of soil enzymes are summarized in this paper. The foregone research results discover the close relationship between soil enzyme activity and soil quality (including soil chemical, physical and biological properties), and long-or short-term response of soil enzyme activity to disturbance of soil ecosystem. Meanwhile, soil enzyme activity is sensitive to slightly change of soil quality, which suggests soil enzyme activity can act as one of key indicators for assessment and forecast of soil quality. Some problems in soil enzyme studies are discussed and further possible research of soil enzyme activity is also presented. Ref展开更多
Based on a 1998 survey of urban residents in four Chinese cities, this article presents a rationalist interpretation about the determinants of social trust. It first breaks trust into four categories, namely, trust in...Based on a 1998 survey of urban residents in four Chinese cities, this article presents a rationalist interpretation about the determinants of social trust. It first breaks trust into four categories, namely, trust in family members, trust in friends, trust in acquaintances, and trust in strangers, the last of which is called “social trust”. After reviewing the existing theories of social trust, the second section puts forward a hypothesis that the more resources one possesses, the more likely s/he trusts others. This is so because when one owns more resources, her/his “disaster threshold” would be higher and s/he would be less vulnerable to potential losses due to others’ untrustworthiness. The final section finds empirical evidence to support this rationalist interpretation.展开更多
文摘总结了近年来在全国粮食主产区进行的1 333个田间试验结果,分析了目前条件下中国主要粮食作物水稻、小麦和玉米氮磷钾肥的偏生产力、农学效率、肥料利用率和生理利用率等,发现水稻、小麦和玉米的氮肥农学效率分别为10.4 kg kg-1、8.0 kg kg-1和9.8 kg kg-1,氮肥利用率分别为28.3%、28.2%和26.1%,远低于国际水平,与20世纪80年代相比呈下降趋势。造成肥料利用率低的主要原因包括高产农田过量施肥,忽视土壤和环境养分的利用,作物产量潜力未得到充分发挥以及养分损失未能得到有效阻控等。要大幅度提高肥料利用率就必须从植物营养学、土壤学、农学等多学科联合攻关入手,充分利用来自土壤和环境的养分资源,实现根层养分供应与高产作物需求在数量上匹配、时间上同步、空间上一致,同时提高作物产量和养分利用效率,协调作物高产与环境保护。
文摘The origin and classification of soil enzymes are summarized in this paper. The foregone research results discover the close relationship between soil enzyme activity and soil quality (including soil chemical, physical and biological properties), and long-or short-term response of soil enzyme activity to disturbance of soil ecosystem. Meanwhile, soil enzyme activity is sensitive to slightly change of soil quality, which suggests soil enzyme activity can act as one of key indicators for assessment and forecast of soil quality. Some problems in soil enzyme studies are discussed and further possible research of soil enzyme activity is also presented. Ref
文摘Based on a 1998 survey of urban residents in four Chinese cities, this article presents a rationalist interpretation about the determinants of social trust. It first breaks trust into four categories, namely, trust in family members, trust in friends, trust in acquaintances, and trust in strangers, the last of which is called “social trust”. After reviewing the existing theories of social trust, the second section puts forward a hypothesis that the more resources one possesses, the more likely s/he trusts others. This is so because when one owns more resources, her/his “disaster threshold” would be higher and s/he would be less vulnerable to potential losses due to others’ untrustworthiness. The final section finds empirical evidence to support this rationalist interpretation.
