Mechanical properties of peanut peg after digging and drying

Abstract: In the northern and especially northeastern areas of China, it is so quite pleasantly cool and dry in the autumn that farmers used to cure peanuts in the field for some days after digging in order to decrease the mass of the peanut plants, and more easily transport and pick up the crop. It indicated that the two-stage harvest might be more suitable to peanut production in the north and northeast areas of China. Based on the viewpoint and theory of combining machinery with agronomy, the main peanut varieties in the western of Liaoning were selected as test materials, the variances of moisture content, and mechanical properties of peanut stems and pegs accompanying the change of curing days were studied by means of an infrared moisture meter and a universal bio-material testing machine. During the test, the curing days of peanut plants in the field after digging was selected as the basic variable, and more than seven days as the time span. The moisture contents of peanut stem and peg, and the tensile strength of the peg and its nodes were measured. The change rules of moisture content of peanut plants during the curing process in the field were obtained, which showed that the change rules of three kinds of peanuts were very similar i.e. the moisture content of the peanut stem and peg dropped rapidly with the extension of curing time in the early drying time (previous two days), and then the moisture content decreased slowly. The change rules of moisture content of peanut plants change tended to be an asymptote from the third curing day, when the moisture contents of the peanut stem and peg were almost no longer dropping, and finally settled around 9%. The moisture content of the peanut peg and its two nodes ranged from 8.48% to 65.68%, and the changes of tensile strength and moisture content in the three kinds of peanuts were quite similar. In the whole curing process, the tensile strength of the peanut peg was always highest, the tensile strength of the peanut-peg node was lowest, and the tensile strength of the stem-peg node was in the middle. The tensile strength of the three key positions of the peg all changed with the moisture content. And the tensile strength of the fresh peanut plants with high moisture content were highest, the tensile strength of peanut peg and its two nodes decreased rapidly in the early curing time, and then dropped slowed until it gradually tended to a constant value. The regression equation of the tensile strength and the moisture content of the peg and its two nodes as obtained by the method of SPSS software were that the fitting coefficient of stem-peg node tensile strength was 0.9891, the fitting coefficient of peanut-peg node tensile strength was 0.9974, and the fitting coefficient of peanut peg tensile strength was 0.9966. And under the experimental condition, the optimal curing days before picking up was preliminarily determined to be 3~5d, and the corresponding moisture content of the peanut peg ranged from 10% to 20%, the tensile strength of peanut peg and stem-peg node ranged from 10N to15N, and the corresponding tensile strength of peanut-peg node ranged from 7N to 9N. The above study results could be used as important references to design a picker and thresher of peanuts and to determine the optimal picking time, as well as deeply research the mechanisms of picking up and threshing with less loss of dropping and damage.