**1. Introduction**

Peanut (*Arachis hypogea* L.) is an annual leguminous herb in the rose order, also known as "everlasting pod", "mud-bean", "crocus bean", and so on [1]. Peanut is the fourth largest oil crop in the world [2–4], and it is also one of the most vital oil crops and economic crops that play a crucial role in ensuring domestic edible oil supply and diversifying food consumption in China [5–7]. According to the statistics of the Food and Agriculture Organization (FAO) of the United Nations and the National Bureau of Statistics of China, in 2020, the planting area for peanuts in the world was 3.16 × <sup>10</sup><sup>7</sup> ha with a total yield of 5.36 × <sup>10</sup><sup>7</sup> t, and the planting area for peanuts in China was 4.62 × 106 ha with a total yield of 1.81 × 107 t. The area and total yield were ranked second and first in the world, accounting for 14.63% and 33.64% of the global peanut area and yield, respectively [8,9].

**Citation:** Shen, H.; Yang, H.; Gao, Q.; Gu, F.; Hu, Z.; Wu, F.; Chen, Y.; Cao, M. Experimental Research for Digging and Inverting of Upright Peanuts by Digger-Inverter. *Agriculture* **2023**, *13*, 847. https:// doi.org/10.3390/agriculture13040847

Academic Editor: Alessio Cappelli

Received: 16 March 2023 Revised: 31 March 2023 Accepted: 6 April 2023 Published: 10 April 2023

**Copyright:** © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

The research and development of Chinese peanut production machinery began in the 1960s. After half a century of effort, all the links in peanut mechanization production have made great progress [10–13]. In 2016, the mechanization rates of the three main links of peanut cultivation, sowing, and harvesting were 72.61%, 43.1%, and 33.91%, respectively, and the comprehensive mechanization rate was 52.14% [14]. At present, there are two main operating modes in China's peanut harvesting machinery, which are two-stage harvest and combine harvest [15]. When the two-stage harvester operates, the digging harvester places peanut plant pods in the field facing up, which is conducive to the rapid drying of pods, and it can effectively reduce the occurrence of peanut pod mold in rainy weather [16,17]. Therefore, whether it is abroad or in China, there is a demand for peanut digging harvesting techniques with vines inverting functions. At present, most of the peanut-digging harvesting machines in countries such as the United States have the function of inverting the vines [18]. In China, the two-stage rewarding areas are mainly produced in Huanghuaihai Northeast and Northwest, while the peanuts of Huanghuaihai Marine District are also harvested. It is often harvested in the same season, and the technical demand for digging and harvesting with the function of the vines inverting is the most urgent.

The peanut digger-inverter mainly has an inverting wheel and a curve-type inverting rod mechanism, which can realize the peanut plant pod facing up and orderly inverting laying. In the United States, there are five major agricultural machinery manufacturing companies, including Armadas Industries (AMADAS), Suffolk, VA, USA; Kelley Manufacturing Company (KMC), Tifton, GA, USA; Colombo North America Inc. (COLOMBO), Adel, GA, USA; Ferguson Manufacturing Company (FERGUSON), Suffolk, VA, USA; and Pearman Corporation (PEARMAN), Tifton, GA, USA. They have produced peanut harvesters with a peanut vine inverting function, and their vines inverting mechanisms are similar in structure and have been widely used in the world, but it does not apply to Chinese upright peanuts [19–23]. For example, in 2011, the relevant machine from KMC Company in the United States was introduced into Xinjiang. The peanut varieties planted in Xinjiang are upright and mulched, resulting in poor vine inversion, serious mulching film entanglement, high pod fall and loss rates, and other problems [24]. In combination with the common planting of upright peanut varieties in the main producing areas of China, they generally have the characteristics of an upright and compact plant type, few branches, and a higher main stem. Zhengzhou Xechuang Mechanical and Electrical Equipment Co., Ltd., Zhengzhou, China, independently developed Hongtian 4HS-2 peanut harvester; Heishan County Jianguo Agricultural Machinery Machinery Co., Ltd., Suzhou, China, independently developed Jianguo brand 2H-1 peanut harvester; Shandong Jiarun Heavy Industry Machinery Co., Ltd., Linyi, China, independently developed supply chain peanut harvester, Ministry of Agriculture and Rural Affairs of Nanjing Institute of Agricultural Mechanization independently developed elevator chain peanut harvester; peanut digging and harvesting machines with neat laying functions have been widely used in Shandong, the Northeast, and other major peanut producing areas [25–27]. These machines can only achieve the orderly laying of peanuts and cannot prevent the vines from inverting. On the basis of referring to the harvesting technology of the United States, China has also developed some similar peanut digging and harvesting machines with the function of inverting vines. For example, Mechanical Equipment Research Institute of Xinjiang Academy of Agricultural Reclamation Sciences [28], Zhengyang Chuangxin Machinery Co., Ltd., Zhumadian, China [29], Henan Shifeng Machinery Manufacturing Co., Ltd., Luoyang, China [30], Xinjiang Agricultural University [31], Shenyang Agricultural University [32], Henan Polytechnic University [16], etc., these research results are only reflected in literature and have not been applied in real production practice. Therefore, the optimization of the working parameters of the peanut digger-inverter is helpful to promote the rapid industrialization of the machine.

In view of the current research status of peanut digging and inverting technology in China and abroad, in order to quickly dry the pods and effectively reduce the peanut pod sticking mildew in rainy weather, this paper, combined with the peanut two-stage harvesting mode, used the peanut digger-inverter to conduct experimental research on upright type peanuts under two conditions of unpressed vines and pressed vines, and found the parameters of the peanut digger-inverter suitable for Chinese peanut varieties. It will provide certain technical support for the later design of the peanut digger-inverter and create the hardware foundation for peanut intelligence and information harvesting.
