Development of device for bionic sub-soil liquid fertilizer

Abstract: The conservation tillage and liquid fertilization can enhance the productivity of farmland. However, soil adhesion occurs on the surfaces of soil-tillage implements during liquid fertilizer applications. Soil adhesion phenomenon can increase energy consumption and decreases fertilizer application quality. The working procedure of liquid fertilizer application by sub-soil liquid fertilizer involves soil compression and shearing, hence, the shape and surface features of the sub-soil liquid fertilizer could significantly affect the performance of soil penetrating, in turn, affect the quality of liquid fertilizer application. Improving the shape design of soil engaging tool is one of the effective methods for reducing operating resistance and increasing working quality. Therefore, a sub-soil liquid fertilizer with novel geometries and surface features should be investigated, and attempts should be made to improve operating efficiency of liquid fertilizer application. Biologically inspired engineering is the application of biological methods found in nature to the study and design of engineering systems. When pressed with an engineering problem in agriculture, engineers could find wisdom and inspirations from the natural world. Through learning from the natural world, it is found that the interactions of living organisms with natural surroundings have led to the evolution of biological systems and environmental adaptabilities. Among the living organisms, 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. Besides, earthworms can comfortably move in moist or adhesive soil, it's worth noting that soil particles seldom sticking to bodies. One of the soil fertilization mechanisms for earthworms is that the earthworm swallowed soil and excreted particle casts while burrowing in soil. In this process, the earthworm mucus plays critical roles in adhesion reducing, soil fertilizing and so on. Inspired by this special behavior of earth worm, bionic engineering approach was used and novel method for improving soil fertility were provided in this study. The profile curves of earthworm head and body surface were extracted and fitted using image processing technology. Geometric structure surface of sub-soil liquid fertilizer injection device was designed based on the contour curve equations. The sub-soil liquid injection fertilizer devices (3 injection holes and 6 injection holes) which matched with the bionic subsoiler, were designed. Ultra-high molecular weight polyethylene (UHMWPE) was chosen as the material for manufacture this device. The significant influence of factors for investigation was the liquid injection, the number of holes, the materials and the surface structure for drag resistance, and the surface structure, the number of holes, the materials and the liquid injection for soil adhesion. The prototype performances were tested by using soil bin test system. The performance parameters of holes, liquid injection, material and geometrical structure surface were taken into account to present the effects on drag-reducing and anti-soil adhesion in tests. The results showed that the significant influences of the performance parameters for drag resistance were as liquid injection > hole number > material > surface structure. The significant influences of the performance parameters for soil adhesion were surface structure > hole number > material > liquid injection. The optimal level of each parameter was the liquid injection, six holes, UHMWPE material and geometrical structural surface. The optimized prototype was selected from eight types of sub-soil liquid fertilizer injection devices, which was UHMWPE in material, with geometry structure surface and six liquid injection holes. In the same experiment conditions, the mean value of the drag resistance of the selected bionic prototype was 283.48 N, the mean weight of soil adhesion was 10.93 g, which was lower than that of other prototypes. This study provided technical references for the mechanization of sub-soil fertilizing engineering.