Abstract
Jujube girdling is an important method to improve the yield and quality of jujube fruit. However, girdling usually causes the tearing of jujube bark, resulting in the slow healing and even death of jujube trees. These problems directly affect the economic benefits of jujube planting. In this paper, in order to reveal the tearing mechanism of jujube bark caused by girdling, and provide the basic mechanical parameters of jujube bark for the research and development of automatic girdling equipment, the structure and mechanical characteristics of jujube bark were studied through theory and experimental methods. The results of microscopic observation showed that jujube bark is a biological composite material mainly composed of the phloem, periderm and epidermis. Furthermore, a mathematical model-based analysis of the growth stress of jujube bark showed that growth stress can be regarded as a biaxial stress state, which can promote the longitudinal tearing of jujube bark during girdling. The tensile test results of jujube bark showed that jujube bark belongs to the category of anisotropic and biologic material. Its longitudinal and transverse mechanical characteristics are significantly different. The maximum longitudinal tensile load was in the range of 105.9~293 N, the longitudinal tensile strength was 16.3 MPa and the elastic modulus was 255.6 MPa. The average transverse tensile load was only 27.9% of the longitudinal tensile load. The transverse tensile strength was 3.5 Mpa and its elastic modulus was 724.14 MPa. The transverse cutting test of jujube bark showed that the average cutting force was 118.2 N and the cutting strength was 9.8 MPa. The results of this study showed that both the growth stress and the anisotropic natural polymer of jujube bark have adverse effects on girdling. Subsequently, issues relating to the selection of appropriate girdling tools and the matters needing attention in the process of the girdling operation were proposed, so as to guide the correct application of girdling technology. In addition, some suggestions on the research and development of girdling tools in the future are put forward.
Highlights
Jujube is rich in nutrition, containing extremely high ascorbic acid, a variety of amino acids, and dozens of mineral elements, sugars, phenols and other nutrients, so it is deeply loved by consumers [1,2,3]
It can be seen that the axial growth stress of jujube bark is related to the expansion pressure P at the top of the jujube, and the expansion pressure depends on the growth rate of the jujube
In the present study, aimed at the hypothesis that the physical and mechanical characteristics and growth stress distribution of jujube bark have adverse effects on the jujube girdling, and to find out how they affect the tearing of jujube bark in girdling process, the mechanical characteristics of jujube bark were tested and the growth stress model was built
Summary
Jujube is rich in nutrition, containing extremely high ascorbic acid, a variety of amino acids, and dozens of mineral elements, sugars, phenols and other nutrients, so it is deeply loved by consumers [1,2,3]. In order to improve the yield of red jujube, most varieties such as Hui jujube and winter jujube need to be girdled at the stage of 40% full flowering [7]. The girdling wound that does not heal in time can provide spawning places for pests, resulting in reduced production of fruit trees, and so on. It is of great significance for the sustainable development of the jujube planting industry to find out the reasons for the tearing of jujube bark in the process of girdling in order to reduce the adverse effects of girdling
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