Design of double disc ditching and sowing combined working machine of Astragalus smicus for machine-harvested rice stubble field

Abstract: Astragalus smicus, also known as Chinese milk vetch, Zi yunying and so on, is one of the main winter green manure crops in paddy fields of central and southern China, it has the advantages of reducing fertilizer input, improving soil fertility, increasing crop yield and quality, and protecting ecological environment, and has strong nitrogen fixation ability and high utilization efficiency. In recent years, the production machinery of Astragalus smicus has been developed and applied rapidly in terms of capacity and utilization efficiency, but its development still lags behind. Ditching and sowing are important links in the production of Astragalus smicus. The yield of Astragalus smicus is largely determined by the quality of sowing, and ditching operation can make Astragalus smicus grow well in low-humid field with poor drainage or sandy soil with poor fertilizer and water retention. Astragalus smicus is often used as green manure in paddy field, but high stubble retention, large amount of straw, insufficient in sowing height of existing other sowing equipments, working parts easily clogged, etc., bring difficulties for mechanized production of Astragalus smicus. In order to solve the influence of machine-harvested rice stubble on mechanized production of Astragalus smicus, aiming at the problems of low quality and low production efficiency in independent ditching and sowing links at present, a Astragalus smicus ditching and sowing machine which suitable for machine-harvested rice stubble field was developed. A height adjustable sowing device was designed, by which the sowing components could be lifted to a proper position according to the residual straw situation in the field. The special seed-metering wheel and quantitative evenly-sowed device for Astragalus smicus were developed to achieve precision sowing and improve the sowing uniformity. The structure and working parameters of the double-disk ditching components were determined. The variation coefficients of ditching width and depth determined by field experiments were less than 6%, which met the drainage requirements of Astragalus smicus growth process. The multiple factor experiments and regression analysis of the test data were carried out by Design-expert software, the results showed that forward speed of machine, rotation speed of seed-metering wheel, seed-uniforming cylinder diameter significantly affected the sowing performance, the results of variance analysis showed that the rotation speed of seed-metering wheel had the greatest influence on the emergence rate and coefficient of variation of sowing uniformity, while the forward speed of machine had the least influence on the emergence rate and coefficient of variation of seed-metering quantity consistency, regarding the coefficient of variation of sowing uniformity, the most influential factor was seed-uniforming cylinder diameter, and the minimum impact factor was the rotation speed of seed-metering wheel, the optimal factor parameters combination which affected the sowing quality of Astragalus smicus ditching and sowing machine was as follows: forward speed of machine was 4.6 km/h, rotation speed of seed-metering wheel was 44 r/min, seed-uniforming cylinder diameter was 6 mm. Verified by field experiments, the Astragalus smicus emergence rate was 95.87%, quantity consistency was 12.7%, coefficient of variation of sowing uniformity was 8.07% in the condition of optimal parameter combination, the relative error was below 3% compared with optimal values predicted by the model. Compared with the existing sowing methods of Astragalus smicus, working efficiency of the designed ditching and sowing machine was 1 hm2/h, which was superior to the artificial sowding working efficiency of 0.1 to 0.125 hm2/h, the hand-shaking working efficiency of 0.2 to 0.3 hm2/h and the motorized sowing working efficiency of 0.5 to 0.8 hm2/h, and was lower than the UAV sowing working efficiency of 3 to 4 hm2/h. In addition, the coefficient of variation of sowing uniformity and the combination type of ditching and sowing machine were also significantly superior to that of other methods. The Astragalus smicus ditching and sowing machine developed in the paper integrated ditching and sowing links in one operation, the working efficiency was greatly improved, the research provided a new method for Astragalus smicus ditching and sowing machine for machine-harvested rice stubble field.