Development of the soil layer construction device for the cotton seedbed in sandy soil of arid areas

Cotton planting has widely used the mode of 'dry sowing and wet emergence' in the sandy soil of arid areas, particularly in southern Xinjiang, China. There are also soft and dry soil textures, as well as the residues of agricultural film. However, the continuous operation of spring tillage and soil preparation has seriously affected the emergence rate of cotton planting, such as the large working resistance, uneven seedling bed, and low pressure. In this study, a seedbed preparation machine was designed suitable for the sandy soil. The multiple operations were realized at one time, including crushing soil, leveling soil, stubble removal, pressing, and grinding. A segmented soil leveling device was also designed to replace the rake group for the joint preparation using the discrete element method (DEM). A two-stage type was then utilized to symmetrically distribute the first section of the scraper in a 'W' shape. The motion analysis was performed to explore the effect of the scraper angle on the soil fluidity, smoothness, and working resistance. Once the inclination angle of the scraper was 45°, better performance was achieved in the crushing soil and leveling soil. A bench orthogonal test was carried out to optimize the influencing factors of the diameter of the press roller, counterweight, and the diameter of the crushing roller in the machine soil layer construction device using the comprehensive scoring method. The construction of the soil layer was evaluated to compare the membership score and variance analysis of soil compactness, depth of repression, and tractive resistance membership degree. The results show that the significant influencing factors were found in the diameters of the press and crushing roller, and there was no influence of the counterweight. The optimal diameter of the press and crushing rollers was both 400 mm. The prototype test showed that the working resistance and fuel consumption were reduced by 8.67% and 5.4%, respectively, whereas, the operating efficiency increased by 6.6%. The standard deviation of surface flatness was 2.8% after two times of equipment preparation. The coefficient of variation of tillage depth stability was 9.2%, and the soil crushing rate was 92.3%, indicating no straw residual film on the surface. The segmented soil leveling device was used to effectively break the soil and stubble. The compaction degrees of 0-20, and 20-50 mm soil layer were 50-100, and 150-200 kPa, respectively. The floating soil layer construction device effectively compacted the soil to construct the soil layer structure of 'upper virtual and lower real'. The average soil compaction degree of the sowing soil layer was 169 kPa suitable for the precision sowing of film mulching and cotton growth in the sandy soil. The dislocation rate of seed film decreased by 62.5%, whereas, the emergence rate was improved by 4.8%, compared with the contrast model. The findings can provide a strong reference to develop the seedbed soil preparation for the cotton film planting in the sandy soil.