Sugar Beet Root Properties in Relation to Harvesting Damage

Sugar beet main roots (MR) break during lifting causing a considerable loss of saleable product in the field. These losses are caused by stresses developed into the MR during lifting. In this work an analysis of the strength of beet secondary roots and rootlets as well as the tensile, compressive, shear and bending strength of MR parts is presented. The main root is composed, from the strength point of view, of two materials: (1) The parenchyma which is more abundant in the inner parts. It is relatively weak in tension (mean strength 2.1 MPa, range 0.65-4.29 MPa) but stronger in compression (mean strength 3.05 MPa range 2.50-4.00 MPa ) and (2) The vascular tissue, which forms several rings within the parenchyma. The rings are denser in the outer parts of the root especially near the epidermis. The vascular tissue is stronger in tension than the parenchyma (mean strength in tension of outer parts of root 2.8 MPa range 1.4 -4.46 MPa). It was found that secondary roots and rootlets required an average force of 39.6 N to break sections of 15 mm in diameter. The main mean root shear strength was 0.60 MPa when the shearing load was applied at the plane normal to the plane including the root grooves and 0.68 MPa at the plane including the root grooves. When the main root was subject to bending the maximum strength in tension or compression of the outer layers depends on the dimensions of the breaking section. Two exponential relationships and one inverse were fitted to the data, which can be used in modelling sugar beet lifting. The exponential formulae gave a better and more realistic approximation of the root strength.