Influence of soil strength on root growth: experiments and analysis using a critical-state model
Influence of soil strength on root growth: experiments and analysis using a critical-state model
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DOI：
10.1046/j.1365-2389.2002.00429.x
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发表时间：
2002-03-01
影响因子：
4.2
通讯作者：
Bengough, AG
中科院分区：
文献类型：
--
作者：
Kirby, JM;Bengough, AG
根在压实的土壤中生长得更粗，尽管大物体穿透土壤需要比小物体更大的力。我们根据形状恒定的根部穿透周围的应力来检查加厚的优势，而不是像之前研究的那样根据膨胀的圆柱体或球体周围的应力。我们结合了压实土壤中生长的根部周围应力的实验和模拟。我们测量了四种不同密度下在沙壤土和粘壤土中生长的豌豆根的直径，以及土壤的临界状态特性。在渗透阻力约为 1 MPa 时，砂壤土中的根部直径比 0.7 MPa 时大约 40%，在 2 MPa 时约大 60%。在粘壤土中，增稠程度较小——在 1 MPa 时增厚约 10%，在 1.5 MPa 时增厚约 20%。使用临界状态有限元模型预测最大轴向应力位于根帽的最尖端。当根部和土壤之间存在摩擦时，预测尖端处的剪应力值比尖端后面的值更小。当土壤和根部之间的界面被假定为无摩擦时，根据定义不存在剪切应力。在无摩擦的情况下，根部增厚对于缓解根尖峰值应力的优势被削弱了。据预测，粘壤土中的轴向应力和剪切应力比沙壤土中的小，这可以解释为什么这种土壤中的根部没有增厚，尽管其渗透阻力相似。我们的结果表明，根部在其尖端附近所经历的轴向应力和剪切应力的局部值在限制根部生长方面可能与总穿透阻力一样重要。
Roots grow thicker in compacted soil, even though it requires greater force for a large object to penetrate soil than it does for a small one. We examined the advantage of thickening in terms of the stresses around a root penetrating with constant shape, rather than the stresses around an expanding cylinder or sphere, as has been studied previously. We combined experiments and simulations of the stresses around roots growing in compacted soils. We measured the diameter of pea roots growing in sandy loam and clay loam at four different densities, and the critical-state properties of the soils. At a penetration resistance of about 1 MPa the diameter of the roots in the sandy loam was about 40% greater than that at 0.7 MPa, and at 2 MPa it was about 60% greater. In the clay loam, there was less thickening - about 10% greater at I MPa and about 20% greater at 1.5 MPa. The maximum axial stresses were predicted using a critical-state finite-element model to be at the very tip of the root cap. When there was friction between the root and the soil, shear stresses were predicted with smaller values at the tip than just behind the tip. When the interface between the soil and the root was assumed to be frictionless, there were by definition no shear stresses. In the frictionless case the advantage of root thickening on relieving peak stress at the root tip was diminished. The axial and shear stresses were predicted to be smaller in the clay loam than in the sandy loam and may explain why the roots did not thicken in this soil although its resistance to penetration was similar. Our results suggest that the local values of axial and shear stresses experienced by the root near its tip may be as important in constraining root growth as the total penetration resistance.