The effect of soil strength on germination and emergence of wheat (Triticum aestivum L.). II. High shear strength conditions

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Abstract
Experimental studies on limiting soil strength conditions for germination and emergence of wheat are reported. From the experimental results in a fine, dense sand a quantitative estimate of the stresses at the organ/soil interface that will prevent seed and seedling expansion and hence prevent germination and emergence is made using the Spherical Cavity Expansion Theory of Vesic. Interfacial stresses of 3.0, 2.3, 1.7 and 0.8 MPa (=30, 23, 17 and 8 bar) are found to be limiting to germination, root elongation, coleoptile elongation and emergence of wheat respectively. These results are discussed in terms of a range of soils with different mechanical properties. The limiting stresses are interpreted in terms of the results obtained by the torsional shear box.