Root harvester machine: a review of papers from the Scopus database published in English for the period of 1982-2022

. Agricultural products, including root fruits, make up a large part of a person's vital needs. Therefore, cultivating root fruits and harvesting crops without harm is one of the main tasks of agricultural events. Considering the above, it is of great importance to have information about the scientific research and scientific results achieved by our scientists in this field. To this aim, a bibliometric analysis of articles on root harvesters published in the Scopus database between 1982 and 2022 was used to understand the current state of studying cultivating agricultural products, including root fruits, and harvesting their crops and to provide references for future studies. To carry out this research different tools such as Office Excel 2021, VOS Viewer and Mapchart.net were used. The literature retrieved totaled 201 articles, of which 70% were research papers. During the last four decades, the quantity of published papers has increased significantly. For example, there were 22 papers published in 2019, 22 times increase over the number of papers published in 2002 (1 paper). It was found that the top five countries that published the most literature were China, the United States, India, the United Kingdom, and Canada, which published 44, 43, 12, 12, and 10 articles, respectively. During the chosen period 159 authors from 58 countries contributed to the given field.


Introduction
Agriculture is one of the most important parts of any country [1]. It is for this reason that the importance of improving the efficiency of harvesting, including reducing energy consumption and increasing the speed of the harvester, is increasing day by day [2]. To increase the productivity and sustainability of agriculture, technologies and technical means of tillage, sowing and harvesting of agricultural crops and their primary processing have been developed and improved [3], [4]. An important reserve for increasing crop yields is creating optimal soil conditions for the development of the root system of plants [5]. With the development of science and technology, scientists have developed many technological methods of cultivating agricultural crops (Udompant et al., 2021). In many countries of the world, research work is underway aimed at developing new scientific and technical foundations for resource-saving technologies that ensure the movement and separation of a layer with dug roots at lower energy costs, as well as separation from the soil and laying them in a swath without damage [8], [9]. In this regard, an important task is considered to be the implementation of scientific research in such areas as the provision of energy-saving methods with the development of sectional undercut plowshares and the use of side discs, the development of paddle beaters to intensify the soil separation process [2], [10].
Currently, root crops are planted and cultivated on 30-35 million hectares of land all over the world [11]. The cultivation and harvesting of root crops is an important component of agricultural production in almost all countries. At the same time, much attention is paid to the development of highly efficient and resource-saving technical means that ensure the digging of root crops with minimal energy consumption [12], [13]. The variety of climates, soil conditions and water supply of each region around the world, causes a variety of difficulties in the harvesting of root crops. For example, in the soil and climatic conditions of Uzbekistan (high summer temperatures, low relative humidity, soil compaction after irrigation), in the process of harvesting root crops, the soil of the tuberous layer disintegrates into large soil lumps that are harder than root crops, thereby making it difficult to separate it from root crops at the elevator. This circumstance is the main reason that prevents the introduction of root and tuber harvesters [14]. When harvesting the root fruit crop, it is desirable to use the necessary techniques, depending on the season [15].
Bibliometric analysis is a useful tool to analyse publications in a certain research field. It is a quantitative approach to study the metadata of scientific publications in contrast to the qualitative approach of narrative scientific literature reviews, which might often be subject to bias by the researcher [16]. However, bibliometric analysis might also be flawed because publication numbers do not necessarily indicate the importance of a certain research subject. But bibliometrics is a helpful method to detect research trends, whereas a narrative literature review is more suited to compiling scientific knowledge on a certain research field and to identify research deficits. Bibliometric studies in agriculture have been conducted regarding various research aspects, e.g. agriculture [17], food supply chains [18], biostimulants [19], crop-livestock systems [20], rainwater harvesting [21], unnamed aerial vehicles [22] and landslides [23]. The aim of this study is to analyse hot topics and important regions of root harvesters research as well as to use historical bibliometric data to gain new insights into trends and emphasis of international agriculture research.

Dataset and methodology
In this article, we went to the selected publications on worldly knowledge from the research done. The search collects the English-language academic literature retrieved from the Scopus database for the period 1982-2022. The analysis was carried out in September 2022. A total of 201 publications were downloaded with the keywords "root and harvester". In the next step, articles were categorized according to the year of publication. A database of all peerreviewed papers was then created, including the year of publication, authors' names, countries, publication type, journal name, number of citations per paper, the number of citations per journal, the percentage of publications by the topic cluster name and subject area. The analysis was performed using a CSV file, Microsoft Excel 2021, RIS, VOS viewer and Map chart. Figure 1 shows the flow of the selected methodology for the research.
The reasons for our use of the methods mentioned above are related to Scopus, a wellknown database that collects authoritative literature from around the world, especially on irrigation and drainage systems. English is a universal language, therefore, the literature in English is more standard and meaningful than literature in other languages.  The interest in root harvesters started to considerably rise in the second period and the number of published papers consist 86.6% of the total number. However, in the first period, it covers only 13.4%. This research shows the significant concern in the subject of root harvesters.

Journals on root harvester
A wide variety of journals in different parts of the world are used by scholars to publish their research. The communication patterns of the scholars indicate that the total output was distributed across 121 journals published in 58 countries. Of these 10 journals published 39 (32%) papers and the remaining 68% of papers were published in other journals. Table 1 lists the names of the 31 journals which published a minimum of 2 and a higher number of papers during the abovementioned period. The second analyzing criteria is the name of publishing country and impact factor of the top 15 journals (Table 2). Of these fifteen journals were published three from the US, two of them from China, Germany, Switzerland and the other six countries have one journal each from UK, Netherlands, Spanish, Estonian, Japan, Belgium. The average impact factor of the journals with the highest number of articles was 2,24. Among the 15 journals the Soil and Tillage Research had the highest impact factor and the International Journal of Agricultural and Biological Engineering had the highest number of publications in this field.

Authors and their affiliated country
Our research revealed that 159 authors from 58 countries conducted research on root harvesters during 1982-2022. Figure 4 lists 10 authors who published 3 or more papers. Among them, Litak and Bulgakov dominated with 4 research papers followed by Aldraihem, Baglio, Baz, Bilgen, Bowen, Bulsara, Chida and Hoffmann with 3 papers. These mentioned authors published research papers in terms of our field in the second time period during 2002-2022. publications on root harvesters allowed us to determine the influential and productive institutions in this field. As indicated in Fig. 5, of the 10 institutions, four of them were from the US, there were from China, and one each from Ukraine, Poland, and Saudi Arabia. These prolific institutions contributed around 23,8% of the total output. Among these, Jiangsu University occupies the first position in record rank (8 records), followed by the Ministry of Education China (7 records) and the National University of Life and Environmental Sciences of Ukraine (6 records).
The top-ranked countries include the traditionally defined developed countries in the world. The rapid economic growth and agricultural development in PR China, US and India resulted in an increase in agricultural and environmental research, and thus in an increase in publication numbers. This may be mainly due to the fact that these countries host a large number of highly ranked research centers and universities.

Top cited papers on root harvester
A high number of citations indicates the quality and novelty of the research. Teen mostly cited papers on root harvesters are shown in Table 3. A total of 2179 citations were given to 201 publications root harvesters for the given period. Almost 52% of citations were given to 10 papers from Table 3. The First 10 top cited papers are consisting of four conference papers and sex research articles. In this list of most cited papers, the USA has four representations, Canada have two representations, the United Kingdom, China, India and South Africa have one representative each.

Top cited journals on root harvester machine
In the 3.6 subsections, we analyzed the top journals which published the greatest number of papers. Taking into consideration this factor we decided to investigate top-cited journals on irrigation and drainage. Firstly, we sorted source names alphabetically in the excel extension file of 201 documents. Then step by step total papers` citations are summarized by each journal. Interestingly, as a result, we got updating list with potential journal names. The initial 10 journals were selected and shown in Figure 7. Almost 51.26 % (1117 citations) of total citations were given to papers published in these 10 journals. As a result of the number of citations, the first-ranked journal with 2 documents by publication rate emerged as the best journal (see Table 1

Top co-authorships and keywords on root harvester
Co-authorship, keyword co-occurrences, citations, bibliographic coupling, and co-citation maps can be generated using VOSviewer based on bibliographic data. File formats supported include .txt, ris, and .csv from databases such as Web of Science, Scopus. The raw file was imported into VOSviewer and a map of co-authorship and keyword co-occurrences (shown in Figure 8 , 9) were created using the software. The co-authorship analysis resulted in a network of 724 authors. Only authors having a minimum of two publications on the topic of root harvesters were included. As a result, the software generated 24 clusters which included 73 items, 95 links and indicated the total link strength with 172 (Fig. 8). The analysis yielded 1814 keywords. After excluding the general keywords with a low relevance score and those with low occurrence (by default, a minimum of four occurrences of a keyword is selected, to strengthen the co-occurrence results), 46 items were finally identified. Based on the total link strength, each resulting keyword is sketched in a node, creating a network map of all keywords. Figure 9 shows the network map of the top 46 authors' keyword co-occurrence. The size of the node reflects the keyword's degree of importance.

Discussion
Agricultural products are one of human's main sources of food. In agricultural products, root fruits are one of the most important parts. That is why over the past 4 decades, scientific research on root fruits has increased year after year. This is also due to a sharp increase in the number of people worldwide every year. However, science, like all fields, has suffered huge losses due to the COVID-19 virus. We can see this from 2020 when the number of scientific papers on root fruits has decreased slightly.
The developed countries of the world such as China, the USA, India, UK and Canada are conducting the most scientific research on this topic. This is proven by the fact that most of the journals that have published articles on this topic belong to the countries mentioned above. There are several reasons why these countries have a high percentage in this direction: First of all, these countries occupy the leading positions in the world in terms of land area and population. A large population leads to an even greater demand for agricultural products, including root fruits. Therefore, the production of agricultural products and the delivery of quality products to the population are the main means of meeting the vital needs of these countries.
Another important reason is that these countries pay great attention to science. The world's top universities and scientists and professors with a high index are working in these countries. Universities are equipped with the most modern laboratory equipment. Scientists who have made good use of the created opportunities have been publishing the results of their experiments in journals and conferences with the highest index in the world.
In addition, it should be mentioned that these countries are showing great interest in modern agricultural techniques and technologies, modern effective methods. This causes the development of agriculture, including the cultivation of tubers and their quality cultivation. Examples of these include: Indoor vertical farming, farm automation, livestock farming technology, modern greenhouses, precision agriculture, blockchain, artificial intelligence, soil and water sensors, weather tracking, satellite imaging, pervasive automation, minichromosomal technology and etc.
Unfortunately, the Central Asian countries are a little slow in this field, but now the governments and scientists of the Central Asian countries are also interested in this direction.

Conclusion
This research offers a comprehensive bibliometric statistical review related to the literature about root harvesters worldwide between 1982-2022. The main points as key authors, institutions' contribution, geographical locations, top funding sponsors and publishers were discussed and analyzed from obtained data sources. The results demonstrated that the number of publications has increased significantly in the last 14 years. Mostly, scholars preferred to publish their findings in journals in the format of academic research papers (70%). Among journals, the highest contribution was performed in the journal International Journal of Agricultural and Biological Engineering with a total 3,48% of the number of publications. As with the highest impact factor score the journal Soil and Tillage Research was in the leading position with 7,3. In fact, it was found that Soil Use and Management was the most cited journal compared to other journals. The most active authors were identified Bulgakov and Litak. In terms of institution, funding sponsor and publisher the first places took National Natural Science Foundation of China, National Key Research and Development Program of China respectively. Geographically, China was the top country with 44 publications. Engineering and Agricultural and Biological Sciences were the two most chosen subject areas in our research field. The co-authorships were mostly distributed among researchers as Litak G, Bulgakov V, Wu J and others. In co-occurrence, the keywords "energy harvesting", "harvesters" and "harvesting" were the most popular keywords.
This study provided a wide range of views which might be helpful for further analyses. This article can be used as a good scientific database for scientists doing scientific research related to root fruits in the field of agriculture. It will be especially useful for young scientists who are just starting to work on this topic. Important information such as which scientists are working in this field in the world, and in which countries this topic is relevant is given.