Design and parameter optimization of earthworm-like multi-function opener

Abstract: Insufficient soil moisture content and accumulated temperature of the plow layer during springtime tillage in Northeast China severely restrict soybean root growth and soybean development. Aiming at these issues, bionics structure design and theoretical analysis were methodologically combined to design an earthworm-like multi-function opener, which has the function of loosening, furrowing and compaction. This machine could simulate the movement of the earthworm to loose surface soil of plow layer and compact subsoil of seed ditch, which could build favorable seedbeds with soft surface soil and the compacted subsoil, and then significantly raise the soil temperature and soil moisture content of plow layer, which could significantly promote soybean emergence and development. Parameter optimization experiments and regression analysis methods were adopted to study how key structure parameters and operating speed of earthworm-like multi-function opener affected average soil temperature (0-100 mm), average soil moisture (0-100 mm) and emergence time of soybean. Experiment data obtained were assessed by the analysis of variance (ANOVA) and quadratic regression model was set up for optimization by response surface methodology with Design-Expert. Analyses showed that operating speed, scarification mechanism bump height and number of crests of corrugated disk had a significant effect (P<0.01) on average soil moisture content (0-100 mm), average soil temperature (0-100 mm) and average emergence time. Operating speed had a significant interaction with bump height and number of crests respectively and there was no interaction between bump height and number of crests. The average soil moisture content (0-100 mm) decreased with the increase of the advancing operating speed, and the decline trend gradually decreased. The average soil moisture content (0-100 mm) decreased with the increase of the bump height and the number of crests, and the decline trend gradually decreased. The average soil temperature (0-100 mm) increased with the acceleration of the operating speed, and the upward trend slowed down gradually. With the increase of bump height and the number of crests, the average soil temperature (0-100 mm) presented a rising tendency, and the rising trend decreased gradually. With the increase of operating speed, the average emergence time decreased first and then increased. The average emergence time of soybean increased after slight decrease with the increase of the height of bump. As the number of crests increased, the average emergence time decreased at first, and then rose. Earliest average emergence time was taken as main optimization index to obtain the optimal parameters by using MATLAB software based on the analysis of the test results and the model fitting. It was found that the optimal parameters of earthworm-like multi-function opener were as follows: operating speed of 8 km/h, bump height of 6 mm and number of crests of 15. Compared with traditional single disk and double-disk opener, earthworm-like multi-function opener could increase average soil water content (0-100 mm) by 5.92% and 4.86%, raise average soil temperature (0-100 mm) by 0.5 and 0.4 ℃, and advance soybean emergence time by 0.5 and 0.92 d, respectively. The results showed that the scarification furrowing mechanism which simulates the biological behavior of earthworms could effectively loosen the plow layer soil and increase the soil porosity in the plow layer so as to effectively improve the soil temperature. Meanwhile, pressure regulating mechanism could significantly accelerate the absorption of moisture from the soil beneath the plow layer by compacting subsoil of seed ditch, and then increase the soil moisture content of the soil in plow layer. This new machine can improve physical properties of the soil in tillage layer, and ultimately achieve the purpose of promoting soybean development. This is a powerful guarantee for production of soybean per unit area in Northeast China.