Development of the seed-ditch compaction device for wide-boundary sowing wheat

Wide-boundary sowing pattern of winter wheat has been one of the most important planting types in the rice–wheat rotation areas, such as the Huang Huai Hai region of China. The sowing operations also dominate the wheat yield. In this study, a seed-ditch compaction and sowing device was designed to construct a high-quality seed bed for the winter wheat with a wide boundary. A baffle was also used to improve the flatness of the seed ditch. Among them, the soil failed to cover the seeds, when the seed fell to the seed-ditch. The uncovered seed was directly compressed into (and with) the soil by the compaction wheel, particularly for better contact between seed and soil. As such, a seed-bed environment was formed with the soft on the top and the firm on the bottom, in order to improve the quality of wheat-sowing operations. A systematic analysis was then made to determine the forces during seed-ditch compaction and sowing. The seed-ditch formation was also explored to optimize the parameters with the need for agricultural practices. An optimal combination was achieved for three main parameters, including the spring working shape variable, the relative height of the compaction wheel and the baffle. Specifically, the spring working shape variable was 30-70 mm, the relative height of the compaction wheel was 10-50 mm, and the relative height of the baffle was 0-100 mm. A response surface method (RSM) with a Box-Behnken design (BBD) was used to conduct a three-factor, three-level field experiment. The relative height of the baffle, the relative height of the compaction wheel, and the variable of the spring working shape were taken as the experimental factors, whereas, the qualified rate of sowing depth, the stability coefficient of sowing depth, and the solidity of seed-ditch were as the experimental indicators. The optimal combination of parameters was obtained for the seed-ditch compaction. The relative height of the baffle was 56.6 mm, the relative height of the compaction wheel was 22.4 mm, and the variable pitch of the spring working shape was 48.2 mm. Meanwhile, the key structures were designed, such as the double disk opener, compaction wheel, tensile spring, baffle and soil-covering mechanism. A quadrilateral profiling mechanism was adopted for the overall framework of the device. The better adaptability of terrain types was also achieved for the stability of the single sowing depth. The kinematic and force analyses of the profiling mechanism demonstrated that the upper profiling of the mechanism was, the lower profiling. A double-beam structure was adopted for the upper and lower connecting rods of the parallelogram mechanism. Additionally, a compaction test was conducted under the optimal combination of parameters, compared with the traditional soil-covering compaction device. The results showed that the coefficient of variation was 63.6% lower in the seed-ditch compaction device than in the traditional soil-covering one. There was an increase of 47 kPa in the soil firmness of the seed-ditch compaction device for the soil layers in the depth range of 50-100 mm. The seed-ditch flatness of the compaction device also increased by 63%, compared with the soil-covering compaction device. The compaction wheel flattened the seed, the protruding soil blocks, and the loose soil after the seed fell into the seed-ditch, thus flattening and stabilizing the seed-ditch. The seeds were also embedded more tightly within the soil forming the surface of the seed trench, for the better stability of the sowing depth. The soil firmness of the soil layer from 50-100 mm depth was significantly changed after the seed-ditch compaction. A baffle was then installed behind the double disk in the seed-ditch compaction device, in order to prevent the soil backflow into the outside of the seed-ditch before compaction. The soil below the baffle was backfilled at the bottom of the ditch for the protruding points flat, indicating the better flatness of the ditch bottom. This finding can also provide the equipment support and technical reference for the wheat sowing in the Huang Huai Hai region of China.