为探明刈割与施肥影响河西地区豆禾混播草地稳定性的生态学机理,本研究以‘清水’紫花苜蓿(Medicago sativa)、无芒雀麦(Bromus inermis)和长穗偃麦草(Elytrigia elongata)建植的混播草地为对象,设置3个留茬高度(5 cm(A_(1)),8 cm(A_(2)...为探明刈割与施肥影响河西地区豆禾混播草地稳定性的生态学机理,本研究以‘清水’紫花苜蓿(Medicago sativa)、无芒雀麦(Bromus inermis)和长穗偃麦草(Elytrigia elongata)建植的混播草地为对象,设置3个留茬高度(5 cm(A_(1)),8 cm(A_(2))和11 cm(A_(3)))和6个施肥处理(CK(B_(1)),150 kg P_(2)O_(5)·hm^(-2)(B_(2)),75 kg N·hm^(-2)+225 kg P_(2)O_(5)·hm^(-2)(B_(3)),150 kg N·hm^(-2)+150 kg P_(2)O_(5)·hm^(-2)(B_(4)),150 kg N·hm^(-2)(B_(5)),225 kg N·hm^(-2)+75 kg P_(2)O_(5)·hm^(-2)(B_(6))),并对各草种的生态位特征进行了分析。结果表明:相较于留茬高度,牧草重要值对施肥的响应更敏感,然而提高留茬可增加无芒雀麦重要值并控制过高的紫花苜蓿重要值,其中A_(2)B_(3)处理效果最好;A_(1)可增大各牧草生态位宽度,且均在第3茬的A_(1)B_(4)处理最大;紫花苜蓿与无芒雀麦、紫花苜蓿与长穗偃麦草、无芒雀麦与长穗偃麦草间的生态位重叠分别在第2茬的A_(2)B_(6),A_(2)B_(1)和A_(2)B_(6)处理最小。本研究认为:留茬8 cm,施150 kg N·hm^(-2)+150 kg P_(2)O_(5)·hm^(-2)氮磷肥对实现河西地区豆禾混播草地物种和谐共存及群落结构的长期稳定具有良好效果。展开更多
The overturning stability is vital for the retaining wall design of foundation pits, where the surrounding soils are usually unsaturated due to water draining. Moreover, the intermediate principal stress does affect t...The overturning stability is vital for the retaining wall design of foundation pits, where the surrounding soils are usually unsaturated due to water draining. Moreover, the intermediate principal stress does affect the unsaturated soil strength; meanwhile, the relationship between the unsaturated soil strength and matric suction is nonlinear. This work is to present closed-form equations of critical embedment depth for a rigid retaining wall against overturning by means of moment equilibrium. Matric suction is considered to be distributed uniformly and linearly with depth. The unified shear strength formulation for unsaturated soils under the plane strain condition is adopted to characterize the intermediate principal stress effect, and strength nonlinearity is described by a hyperbolic model of suction angle. The result obtained is orderly series solutions rather than one specific answer; thus, it has wide theoretical significance and good applicability. The validity of this present work is demonstrated by comparing it with a lower bound solution. The traditional overturning designs for rigid retaining walls, in which the saturated soil mechanics neglecting matric suction or the unsaturated soil mechanics based on the Mohr-Coulomb criterion are employed, are special cases of the proposed result. Parametric studies about the intermediate principal stress, matric suction and its distributions along with two strength nonlinearity methods on a new defined critical buried coefficient are discussed.展开更多
文摘为探明刈割与施肥影响河西地区豆禾混播草地稳定性的生态学机理,本研究以‘清水’紫花苜蓿(Medicago sativa)、无芒雀麦(Bromus inermis)和长穗偃麦草(Elytrigia elongata)建植的混播草地为对象,设置3个留茬高度(5 cm(A_(1)),8 cm(A_(2))和11 cm(A_(3)))和6个施肥处理(CK(B_(1)),150 kg P_(2)O_(5)·hm^(-2)(B_(2)),75 kg N·hm^(-2)+225 kg P_(2)O_(5)·hm^(-2)(B_(3)),150 kg N·hm^(-2)+150 kg P_(2)O_(5)·hm^(-2)(B_(4)),150 kg N·hm^(-2)(B_(5)),225 kg N·hm^(-2)+75 kg P_(2)O_(5)·hm^(-2)(B_(6))),并对各草种的生态位特征进行了分析。结果表明:相较于留茬高度,牧草重要值对施肥的响应更敏感,然而提高留茬可增加无芒雀麦重要值并控制过高的紫花苜蓿重要值,其中A_(2)B_(3)处理效果最好;A_(1)可增大各牧草生态位宽度,且均在第3茬的A_(1)B_(4)处理最大;紫花苜蓿与无芒雀麦、紫花苜蓿与长穗偃麦草、无芒雀麦与长穗偃麦草间的生态位重叠分别在第2茬的A_(2)B_(6),A_(2)B_(1)和A_(2)B_(6)处理最小。本研究认为:留茬8 cm,施150 kg N·hm^(-2)+150 kg P_(2)O_(5)·hm^(-2)氮磷肥对实现河西地区豆禾混播草地物种和谐共存及群落结构的长期稳定具有良好效果。
基金Project(41202191)supported by the National Natural Science Foundation of ChinaProject(2015JM4146)supported by the Natural Science Foundation of Shaanxi Province,ChinaProject(2015)supported by the Postdoctoral Research Project of Shaanxi Province,China
文摘The overturning stability is vital for the retaining wall design of foundation pits, where the surrounding soils are usually unsaturated due to water draining. Moreover, the intermediate principal stress does affect the unsaturated soil strength; meanwhile, the relationship between the unsaturated soil strength and matric suction is nonlinear. This work is to present closed-form equations of critical embedment depth for a rigid retaining wall against overturning by means of moment equilibrium. Matric suction is considered to be distributed uniformly and linearly with depth. The unified shear strength formulation for unsaturated soils under the plane strain condition is adopted to characterize the intermediate principal stress effect, and strength nonlinearity is described by a hyperbolic model of suction angle. The result obtained is orderly series solutions rather than one specific answer; thus, it has wide theoretical significance and good applicability. The validity of this present work is demonstrated by comparing it with a lower bound solution. The traditional overturning designs for rigid retaining walls, in which the saturated soil mechanics neglecting matric suction or the unsaturated soil mechanics based on the Mohr-Coulomb criterion are employed, are special cases of the proposed result. Parametric studies about the intermediate principal stress, matric suction and its distributions along with two strength nonlinearity methods on a new defined critical buried coefficient are discussed.
