Experiment and optimization of sub-soil liquid fertilizer injection device

In recent years, subsoiling has been proposed as an alternative means of applying fertilizer into infertile subsoils. It was believed that root growth in the subsoiled channels would be stimulated in this way, and yields would be further increased as a result of the deep-placed fertilizer and better growing conditions. Filed test results from different cultivation areas increasingly have showed that subsoil fertilization resulted in increased crop yields when compared with subsoiling alone. However, two of the disadvantages associated with sub-soil liquid fertilizer application system is the severe soil adhesion phenomenon and high draft requirement, which seriously deteriorate operating quality and restrict its field application. To optimize sub-soil liquid fertilizer injection device, mitigate the problems mentioned above and then extend sub-soil liquid fertilizer application, the technical approach of bionic engineering was adopted. From the perspective of natural environment, the interactions of living organisms with natural surroundings have led to the evolution of biological systems and environmental adaptabilities. Earthworms have long been acknowledged to largely contribute to the aggregate stability of soils varying in texture, carbonate, and concentration of organic matter by burrowing, foraging, and casting on the soil surface and within the soil. Earthworms can readily move in moist or adhesive soil with soil particles seldom adhering to bodies. From the perspective of bionic engineering, the excellent properties of earthworm could be used to inspire the design and optimization of sub-soil liquid fertilizer injection device. One of the mechanisms of reducing soil adhesion for earthworms was that earthworms possess special geometrical structure on their heads and epidermis. The profile curves of earthworm head and body surface were extracted and fitted. Geometric structure surface of sub-soil liquid fertilizer injection device was designed based on the contour curve equations, and the structural parameters were determined. In order to explore the influence of working parameters on working resistance and soil adhesion during the operation of sub-soil liquid fertilizer injection device, and to optimize its operating parameters. Eventually, in the hope of ensuring and improving the working quality of the sub-soil liquid fertilizer injection device. In this study, the Box-Behnken experimental optimum design methods were used. The working parameters of tillage depth, flow rate and speed were chosen as independent variable, to evaluate the effects on response values of drag-reducing and anti-soil adhesion. By building an agricultural soil tank test platform system, the field operating environment were simulated. Then, optimization tests of working parameters of the sub-soil liquid fertilizer injection device were conducted. After that, the multivariate quadratic polynomial regression equations were built. According to the relationship between the independent variable and the response value, the working parameters of the sub-soil liquid fertilizer injection device were optimized. The results showed that the regression equation model based on soil adhesion and working resistance was adequate. It was found that the working parameters of tillage depth, flow rate and speed influenced drag resistance and soil adhesion significantly. Tillage depth and speed presented interaction effects, which influenced drag resistance and soil adhesion with high significance. The significant influences of the experimental factors for drag resistance and soil adhesion were as follows: the tillage depth, speed and flow rate. The working parameters were optimized as follows: the tillage depth was 11 cm, speed was 1.0 m/s, flow rate was 350 g/s. Under the above conditions, the mean value of the drag resistance of the selected bionic prototype was 260.01 N, the mean weight of soil adhesion was 8.73 g. This study can provide technical references for the mechanization of sub-soil fertilizing engineering. © 2020, Editorial Department of the Transactions of the Chinese Society of Agricultural Engineering. All right reserved.