ETUDE MECANIQUE DE L'EMERGENCE DE LA CAROTTE A TRAVERS DES CROUTES SUPERFICIELLES
A mechanical failure model based on bending failure of round plates was tested under controlled laboratory conditions. The purpose was to use statistical distribution of the emergence forces of the seedling to calculate the probability of emergence through the soil crusts of known charateristics.
The emergence force of the sedling was measured using a device developed and proven effective in the laboratory. for carrots, it appeared that the emergence force of the hypocotyl should be determined from its pattern of morphological change in the course of its underground growth, as a function of the initial weight of the seed.
According to the results, the emergence force begins to decrease when the reserves are redistributed within the seedling, declining from 10g to about 3–4g in the larger seeds, and from 6g to 2g in the smaller seeds.
Crusts of continuous and homogeneous peoperties were manufactured from a soil paste to exhibit the ultimate strength measured in the laboratory. The geometry of the crust used in measurements was strictly identical to that of crusts used in experimental determination of the rate of emergence.
We proceed to monitor emergence of carrot sedlings from two different seedweight categories, the age of which corresponded to the period of maximum emergence force.
The percentage of emergence calculated based on the hypothesis of bending failure is in good agreement with the experimental rate of emergence as a function of the strength of the crusts. This rate provides a good indication of the variation in seedling emergence capacity according to the initial weight of the seeds.