The nature of the mechanical impedance to seedlings by soil surface seals

Abstract

The nature of seedling emergence through soil surface seals under a variety of field and model situations is described. In this process the importance of the shear and compressive strengths of the seal has been demonstrated. Resistance to emergence has been shown to be also due to gravity, soil cohesion, and friction between structural parts. The mechanics of seedling emergence is too variable and complex to be expressed by a single index, such as the tensile strength of free samples, as in the modulus of rupture determinations of Richards (1953). Direct measurement of mechanical impedance is preferable to refining the use of such indices, and provides a basis for a better understanding of the relation between seedlings and soil properties influencing emergence.