The objective of this study was to determine the efficiency of different plant systems in capturing deep soil nitrate （NO3-） to reduce NO3- leaching in a field plot experiment using 15N labelling. The study was cond...The objective of this study was to determine the efficiency of different plant systems in capturing deep soil nitrate （NO3-） to reduce NO3- leaching in a field plot experiment using 15N labelling. The study was conducted on a calcareous alluvial soil on the North China Plains and the plant systems evaluated included alfalfa （Medicago sativa）, American black poplar （Populus nigra） and cocksfoot （Dactylis）. ^15N-labelled N fertilizer was injected to 90 cm depth to determine the recovery of ^15N by the plants. With conventional water and nutrient management, the total recovery of ^15N-labeled NO3--N was 23.4% by alfalfa after two consecutive growth years. The recovery was significantly higher than those by American black poplar （12.3%） and cocksfoot （11.4%）. The highest proportion of soil residual ~SN from the labeled fertilizer N （%Ndff） was detected around 90 cm soil depth at the time of the 1st year harvest and at 110-130 cm soil depth at time of the 2nd year harvest. Soil %Ndff in 0-80 cm depth was significantly higher in the alfalfa treatment than those in all the other treatments. The soil %Ndff below 100 cm depth was much lower in the alfalfa than those in all the other treatments. These results indicated that ^15N leaching losses in the alfalfa treatment were significantly lower than by those in the black poplar and cocksfoot treatments, due to the higher root density located in nitrate labeling zone of soil profile. In conclusion, alfalfa may be used as a plant to capture deep soil NO3- left from previous crops to reduce NO3- leaching in high intensity crop cultivation systems of North China Plain.展开更多
目的针对15-5PH钢零件再制造后性能调控缺乏试验和数据支撑的问题,研究热处理温度对15-5PH熔覆层微观组织及力学性能的影响。方法利用冷金属过渡(Cold Metal Transfer,CMT)工艺制备了连续、平整、无宏观缺陷的熔覆层,并采用不同温度对...目的针对15-5PH钢零件再制造后性能调控缺乏试验和数据支撑的问题,研究热处理温度对15-5PH熔覆层微观组织及力学性能的影响。方法利用冷金属过渡(Cold Metal Transfer,CMT)工艺制备了连续、平整、无宏观缺陷的熔覆层,并采用不同温度对熔覆层进行了热处理。利用光学显微镜、XRD、SEM和EDS等手段分析了熔覆层的微观组织、物相组成,通过拉伸试验、剪切试验测试了熔覆层力学性能。结果焊态熔覆层主要由马氏体、铁素体、球状碳化物构成,不同区域的马氏体、铁素体形态有显著差异。随热处理温度的升高,焊道中间区域微观组织差异逐渐减小,尺寸有增加的趋势,经580℃、620℃热处理后,马氏体晶界上生成白色块状逆转变奥氏体,而且逆转变奥氏体含量和尺寸随温度的升高逐渐增加。此外,经450℃热处理后,熔覆层的屈服强度、抗拉强度、剪切强度达到最高,分别为1251、1318、674.9 MPa,伸长率仅为3.6%;当温度高于450℃时,随温度的升高,屈服强度、抗拉强度、剪切强度逐渐降低,伸长率增加。结论探明了热处理温度对再制造15-5PH熔覆层组织和性能的影响规律,为再制造15-5PH零件的热处理提供了依据。展开更多
基金financially supported by the Provincial Natural Science Foundation of Hebei Province in China(C2006000491)the financial support from the National Natural Science Foundation of China(30571110,31172033)the National 863 Program of China(2012AA101403-3)
文摘The objective of this study was to determine the efficiency of different plant systems in capturing deep soil nitrate （NO3-） to reduce NO3- leaching in a field plot experiment using 15N labelling. The study was conducted on a calcareous alluvial soil on the North China Plains and the plant systems evaluated included alfalfa （Medicago sativa）, American black poplar （Populus nigra） and cocksfoot （Dactylis）. ^15N-labelled N fertilizer was injected to 90 cm depth to determine the recovery of ^15N by the plants. With conventional water and nutrient management, the total recovery of ^15N-labeled NO3--N was 23.4% by alfalfa after two consecutive growth years. The recovery was significantly higher than those by American black poplar （12.3%） and cocksfoot （11.4%）. The highest proportion of soil residual ~SN from the labeled fertilizer N （%Ndff） was detected around 90 cm soil depth at the time of the 1st year harvest and at 110-130 cm soil depth at time of the 2nd year harvest. Soil %Ndff in 0-80 cm depth was significantly higher in the alfalfa treatment than those in all the other treatments. The soil %Ndff below 100 cm depth was much lower in the alfalfa than those in all the other treatments. These results indicated that ^15N leaching losses in the alfalfa treatment were significantly lower than by those in the black poplar and cocksfoot treatments, due to the higher root density located in nitrate labeling zone of soil profile. In conclusion, alfalfa may be used as a plant to capture deep soil NO3- left from previous crops to reduce NO3- leaching in high intensity crop cultivation systems of North China Plain.
文摘目的针对15-5PH钢零件再制造后性能调控缺乏试验和数据支撑的问题,研究热处理温度对15-5PH熔覆层微观组织及力学性能的影响。方法利用冷金属过渡(Cold Metal Transfer,CMT)工艺制备了连续、平整、无宏观缺陷的熔覆层,并采用不同温度对熔覆层进行了热处理。利用光学显微镜、XRD、SEM和EDS等手段分析了熔覆层的微观组织、物相组成,通过拉伸试验、剪切试验测试了熔覆层力学性能。结果焊态熔覆层主要由马氏体、铁素体、球状碳化物构成,不同区域的马氏体、铁素体形态有显著差异。随热处理温度的升高,焊道中间区域微观组织差异逐渐减小,尺寸有增加的趋势,经580℃、620℃热处理后,马氏体晶界上生成白色块状逆转变奥氏体,而且逆转变奥氏体含量和尺寸随温度的升高逐渐增加。此外,经450℃热处理后,熔覆层的屈服强度、抗拉强度、剪切强度达到最高,分别为1251、1318、674.9 MPa,伸长率仅为3.6%;当温度高于450℃时,随温度的升高,屈服强度、抗拉强度、剪切强度逐渐降低,伸长率增加。结论探明了热处理温度对再制造15-5PH熔覆层组织和性能的影响规律,为再制造15-5PH零件的热处理提供了依据。
