## 3 Precision Sowing Conditions of consistent Sowing-Depth Regulation
### Consistent Sowing-Depth Regulation Technology--Soil Covering
designed a fertilizer soil-covering device suitable for hilly orchards, which can realize the fertilizer-deep application and complete soil-covering operation simultaneously, through the structural combination of an externally grooved wheel-type fertilizer discharg and spiral churning soil-covering device [48]. [PERSON] et al. designed a film soil-covering device using a scraper lift-belt type. By actively transporting the soil for soil covering, the operational efficiency and soil-covering quality were improved [49]. [PERSON] et al. designed a device for automatically adjusting the soil covering the amount of the transplanting machine. The device obtained the information on the soil-covering amount on the film by measuring the soil thickness while working and controlling the depth of the soil-covering disc under the treatment of the control module to adjust the soil-covering amount and reduce the inconsistency of the soil-covering thickness caused by the uneven ground of the soil-covering device [50]. The current foreign research in soil covering focuses on extruded soil-covering devices, which have a soil-covering and compacting function, and is research based on the same principles in different structural forms. Soil is the primary environment for nutrient supply for crop growth; studies were conducted to investigate the effects of different covering materials on seed germination and development under the same covering conditions. For example, to examine the impact of other covering materials on the yield of large bulbous cap mushrooms, [PERSON] et al. used peat soil, field soil, peat soil + field soil, volume (m\({}^{3}\)) ratio 1:2 composite soil, and grain hull + field soil, volume (m\({}^{3}\)) ratio 1:2 blended soil as covering materials for Stroharia rugoso-annulata. The test results showed that the Stroharia rugoso-annulata emergence was the fastest. The yield and economic benefits were the highest under the soil-covering conditions of grain hull + field soil composite soil [51]. At the same time, according to the theme of \"soil covering\" in the China National Knowledge Infrastructure, 13,400 articles were searched, and the first three studies focused on cultivation techniques such as the soil covering of mushrooms; the research on mulching under precision seeding is still not a hot spot (Figure 9). In summary, the research into soil-covering devices at home and abroad can be divided into three main areas. The first one is the traditional structure optimization design, which generally focuses on the structure of the existing soil-covering device to make micro-innovations. The soil-covering operation under sowing conditions mainly relies on passive methods such as squeezing and gathering to achieve soil coverage of seeds, which is still based on the traditional passive soil-covering operation. The second type is the mechanical type of initial soil covering, designed with a spiral churning soil-covering device to effectively realize the initial nature of the soil-covering process. For complete film soil covering, it is widely used for crops such as essumum and potatoes, which have the advantages of drought resistance. However, there are problems of uneven soil covering and misalignment of cavity holes caused by low soil-covering volume in the way of a simple machine-laying film and manual soil-covering operation. The third is the soil-covering-volume regulation and control, soil-covering-volume automatic adjustment device, and the sowing operational process of quantitative soil covering to achieve consistent sowing depth, which is specifically referenced. The second and third kinds have produced little research on precision seeding operations, mainly focusing on film soil covering and orchard-fertilization soil covering.