The ecogeomorphic processes occurring on semiarid rangelands are reviewed, with emphasis on the source-sink relations and positive feedback loops that existed between shrub patches and intershrub areas, and the way li...The ecogeomorphic processes occurring on semiarid rangelands are reviewed, with emphasis on the source-sink relations and positive feedback loops that existed between shrub patches and intershrub areas, and the way livestock presence affected these interactions. Compared with intershrub areas, the shrub patches had a higher soil porosity, infiltration capacity, water-holding capacity, hydraulic conductivity, structural stability, and organic matter content, and lower bulk density. These differences derived from a host of processes whose intensity was less in the shrub patches, including raindrop impact, mechanical crust formation, overland water flow, soil erosion, evaporative moisture loss, and flock trampling. There was also greater shading of the soil surface; soil and litter deposition; water accumulation; microbial, fungal, and mesofaunal activities in the shrub patches. The overland flow of water carried soil and litter from the intershrub areas to the shrub patches and resulted in microtopographic modifications that tended to strengthen these source-sink relations. Grazing had an impact on these processes, not only at the shrub-intershrub scale but also within the intershrub areas, through the creation of highly compacted trampling routes. The combined role of the above ecogeomorphic processes was to maintain the rangeland＇s functionality. Without these inter-relationships, water loss, soil erosion, and nutrient depletion would occur at the hillside scale, causing degradation of the landscape.展开更多
Labile organic carbon （LOC） is a fraction of soil organic carbon （SOC） with rapid turnover time and is affected by soil fertilization. This investigation characterized the SOC content, LOC content and LOC distribu...Labile organic carbon （LOC） is a fraction of soil organic carbon （SOC） with rapid turnover time and is affected by soil fertilization. This investigation characterized the SOC content, LOC content and LOC distribution in the treatment plots of surface soil erosion at five levels （0-, 5-, 10-, 20- and 30-cm erosion）. The soil had received contrasting fertilizer treatments （i.e., chemical fertilizer or chemical fertilizer ＋ manure） for 6 years. This study demonstrated that both SOC and various LOC fractions contents were higher in the plots with fertilizer ＋ manure than in those with fertilizer alone under the same erosion conditions. The SOC and LOC contents de- creased as the erosion depth increased. Light fraction organic carbon, particulate organic carbon, easily oxidizable organic carbon （KMnO4-oxydizable organic carbon）, and microbial biomass carbon were 27% 57%, 37%-7%, 20%-25%, and 29%-33% higher respectively in the fertilizer ＋ manure plots, than in the fertilizer alone plots. Positive correlations （p 〈 0.05） between SOC content and different fractions contents were observed in all plots except the correlation between total SOC content and water-soluble organic carbon content in the different fertilization treatments. Obviously, fertilizer ＋ manure treatments would be conducive to the accumulation of LOC and SOC in the Black soil of Northeast China.展开更多
Soil erosion affects soil productivity and environmental quality.A laboratory research experiment under simulated heavy rainfall with tap water was conducted to investigate the effects of anionic polyacrylamide(PAM) a...Soil erosion affects soil productivity and environmental quality.A laboratory research experiment under simulated heavy rainfall with tap water was conducted to investigate the effects of anionic polyacrylamide(PAM) application rates(0,0.5,1.0,and 2.0 g m-2) and molecular weights(12 and 18 Mg mol-1) on runoff,soil erosion,and soil nutrient loss at a slope of 5°.The results showed the two lower rates of PAM application decreased runoff while the highest rate increased runoff as compared with the control.Sediment concentration and soil mass loss increased significantly with the increasing PAM application rate.Compared with the control,PAM application decreased K+,NH4+,and NO3-concentrations in sediment and K+ and NH+4 concentrations in runoff,but significantly increased the mass losses of K+,NH4+,and NO-3 over soil surface except for the NH4+ at PAM application rate lower than 1.0 g m-2.PAM application decreased the proportion of K+ loss with runoff to its total mass loss over soil surface from 60.1% to 16.4%.However,it did not affect the NH4+ and NO3-losses with runoff,and more than 86% of them were lost with runoff.A higher PAM molecular weight resulted in less soil erosion and K+ mass loss but had little effect on runoff and NH+4 and NO3-losses.PAM application did not prevent soil erosion and the mass losses of K+ and NO3-under experimental conditions.展开更多
In this study,ogive-nose projectile penetration into concrete slabs was tested at initial projectile impact velocities ranging from 1325.0 m/s to 1425.0 m/s.The depth of penetration and mass loss of the projectiles we...In this study,ogive-nose projectile penetration into concrete slabs was tested at initial projectile impact velocities ranging from 1325.0 m/s to 1425.0 m/s.The depth of penetration and mass loss of the projectiles were measured,and the residual projectiles were recovered after the penetration tests.Scanning electron microscopy and metallographic microscopy of the microstructures were performed on various sections and outer surfaces of the projectiles taken from different locations of the residual projectiles,to analyze the intrinsic mechanisms of mass abrasion.The analysis results reveal that,during high-speed projectile penetration,projectile abrasion is caused by multiple mechanisms.Based on the cavity expansion theory,a projectile penetration model was established by considering the two main mass loss mechanisms observed in the microscopic tests.The theoretical predictions of the penetration depth,mass loss rate,and change of projectile head are consistent with the experimental results obtained both in this study and previous research.展开更多
文摘The ecogeomorphic processes occurring on semiarid rangelands are reviewed, with emphasis on the source-sink relations and positive feedback loops that existed between shrub patches and intershrub areas, and the way livestock presence affected these interactions. Compared with intershrub areas, the shrub patches had a higher soil porosity, infiltration capacity, water-holding capacity, hydraulic conductivity, structural stability, and organic matter content, and lower bulk density. These differences derived from a host of processes whose intensity was less in the shrub patches, including raindrop impact, mechanical crust formation, overland water flow, soil erosion, evaporative moisture loss, and flock trampling. There was also greater shading of the soil surface; soil and litter deposition; water accumulation; microbial, fungal, and mesofaunal activities in the shrub patches. The overland flow of water carried soil and litter from the intershrub areas to the shrub patches and resulted in microtopographic modifications that tended to strengthen these source-sink relations. Grazing had an impact on these processes, not only at the shrub-intershrub scale but also within the intershrub areas, through the creation of highly compacted trampling routes. The combined role of the above ecogeomorphic processes was to maintain the rangeland＇s functionality. Without these inter-relationships, water loss, soil erosion, and nutrient depletion would occur at the hillside scale, causing degradation of the landscape.
基金Under the auspices of National Natural Science Foundation of China(No.41271313,41172229,41071171)Harbin Bureau of Science and Technology for Outstanding Scientist(No.2010FXYN044)
文摘Labile organic carbon （LOC） is a fraction of soil organic carbon （SOC） with rapid turnover time and is affected by soil fertilization. This investigation characterized the SOC content, LOC content and LOC distribution in the treatment plots of surface soil erosion at five levels （0-, 5-, 10-, 20- and 30-cm erosion）. The soil had received contrasting fertilizer treatments （i.e., chemical fertilizer or chemical fertilizer ＋ manure） for 6 years. This study demonstrated that both SOC and various LOC fractions contents were higher in the plots with fertilizer ＋ manure than in those with fertilizer alone under the same erosion conditions. The SOC and LOC contents de- creased as the erosion depth increased. Light fraction organic carbon, particulate organic carbon, easily oxidizable organic carbon （KMnO4-oxydizable organic carbon）, and microbial biomass carbon were 27% 57%, 37%-7%, 20%-25%, and 29%-33% higher respectively in the fertilizer ＋ manure plots, than in the fertilizer alone plots. Positive correlations （p 〈 0.05） between SOC content and different fractions contents were observed in all plots except the correlation between total SOC content and water-soluble organic carbon content in the different fertilization treatments. Obviously, fertilizer ＋ manure treatments would be conducive to the accumulation of LOC and SOC in the Black soil of Northeast China.
基金Supported by the National Natural Science Foundation of China (No.40635027)the Fund of State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau,China (No.10501-169)
文摘Soil erosion affects soil productivity and environmental quality.A laboratory research experiment under simulated heavy rainfall with tap water was conducted to investigate the effects of anionic polyacrylamide(PAM) application rates(0,0.5,1.0,and 2.0 g m-2) and molecular weights(12 and 18 Mg mol-1) on runoff,soil erosion,and soil nutrient loss at a slope of 5°.The results showed the two lower rates of PAM application decreased runoff while the highest rate increased runoff as compared with the control.Sediment concentration and soil mass loss increased significantly with the increasing PAM application rate.Compared with the control,PAM application decreased K+,NH4+,and NO3-concentrations in sediment and K+ and NH+4 concentrations in runoff,but significantly increased the mass losses of K+,NH4+,and NO-3 over soil surface except for the NH4+ at PAM application rate lower than 1.0 g m-2.PAM application decreased the proportion of K+ loss with runoff to its total mass loss over soil surface from 60.1% to 16.4%.However,it did not affect the NH4+ and NO3-losses with runoff,and more than 86% of them were lost with runoff.A higher PAM molecular weight resulted in less soil erosion and K+ mass loss but had little effect on runoff and NH+4 and NO3-losses.PAM application did not prevent soil erosion and the mass losses of K+ and NO3-under experimental conditions.
基金the National Natural Science Foundation of China(Grant No.12032006)Beijing Institute of Technology Research Fund Program for Young Scholars(Grant No.XSQD-202102011).
文摘In this study,ogive-nose projectile penetration into concrete slabs was tested at initial projectile impact velocities ranging from 1325.0 m/s to 1425.0 m/s.The depth of penetration and mass loss of the projectiles were measured,and the residual projectiles were recovered after the penetration tests.Scanning electron microscopy and metallographic microscopy of the microstructures were performed on various sections and outer surfaces of the projectiles taken from different locations of the residual projectiles,to analyze the intrinsic mechanisms of mass abrasion.The analysis results reveal that,during high-speed projectile penetration,projectile abrasion is caused by multiple mechanisms.Based on the cavity expansion theory,a projectile penetration model was established by considering the two main mass loss mechanisms observed in the microscopic tests.The theoretical predictions of the penetration depth,mass loss rate,and change of projectile head are consistent with the experimental results obtained both in this study and previous research.
