Modern agriculture cannot do without the use of mineral and organic fertilizers. Mineral fertilizers are produced by large holdings both in Russia and abroad, and Russian enterprises have subsidiaries distributed throughout the world. The latter factor makes mineral fertilizers one of the most export-oriented branches of the chemical industry in Russia. According to official statistics in 2019 Russian agricultural companies supplied more than 21 million tons of mineral fertilizers to foreign markets, which determines the peculiarities of the country's market. The purpose of the study is to determine the optimal assignment of consumers to suppliers of mineral fertilizers in the organization of multimodal transportation. The article considers the period of the beginning of the reorientation of the production of mineral fertilizers for export. The issue of creating domestic ports specialized in the transshipment of fertilizers has been studied. The volumes of production and consumption of specific countries and regions that are included in export-import operations with each other are analyzed. Routes of transportation of fertilizers with determination of the shortest distances are studied. The optimization of the existing route option for the delivery of nitrogen and potash fertilizers to Brazil is proposed.

Introduction. The paper has developed a new scheme of a multimodal logistics system for grain transportation for export to Iran using links and graphs. It is proposed to consider the functioning of road transport in a multimodal logistics system for grain export from the standpoint of a systematic approach at the micro, meso and macro levels based on the newly introduced concept of transport capacity of the simulated graph. To determine the optimal modes of road transport functioning (with the further aim of increasing its efficiency of functioning) in the logistics links of export grain supplies at the micro level, it is proposed to perform using the ‘Sowing fields – regional barn-floors’ graph, at the meso level – the ‘Regional barn-floors – regional grain storages’ graph, at the macro level – the ‘Regional grain storages – port grain storages’ graph. Graphs modelling, determining the transport capacity of vertices, fixing vertices for barn-floors, regional grain storages and port grain storages make it possible for agro–industrial enterprises to plan the volume of grain exports, to use their acreage rationally considering crop yields while fulfilling an important condition - ensuring food security for the population of the Russian Federation. Road transport planning at the micro level is directly linked to the operation of agricultural enterprises, and at the meso level to grain storages. At the macro level, road transport serves the three largest port grain receiving points of the Volgograd region. Multimodal transportation of grain from a specific farm in the region to the port of Enzeli in Iran has been organized using road transport and VOLGO-BALT 239 river-sea vessel.Materials and methods. The paper uses methods of statistical analysis of winter wheat supplies for export to Iran from the Volgograd region. At the micro level, graphoanalytic methods are used to model the location schemes of filling bunkers when working in a team of one, three or nine combines, indicating their number of appearance on the field in the xOy coordinate plane. The methods of system analysis were used to correctly divide the international multimodal logistics system for the transportation of export grain into micro, meso and macro levels with the definition of the place and role of transport. Methods of solving the linear programming problem are the optimization of the assignment of consumers to suppliers at all levels under consideration.Results. It is revealed that complex international multimodal logistics systems for the delivery of export grain must be considered using a systematic approach. It is proposed to consider the system at the micro, meso and macro levels. At each of the levels, it is necessary to plan the operation of transport based on calculations of the ‘transport capacity’ of the ‘Sowing fields – regional barn-floors’, ‘Regional barn-floors – regional grain storages’, ‘Regional grain storages – port grain storages’ graph nodes. OOO Progress, the agro-enterprise of the Volgograd region, has been given the opportunity to plan its work taking into account new information technologies that ensure higher efficiency of agricultural activities in the cultivation of winter wheat with partial sale for export to Iran.Discussion and conclusions. The improvement of the organisation of road transport functioning in the international multimodal logistics system of grain export supplies cannot exist without the use of precision farming technologies in harvesting and transport processes. The use of the right logistics technologies in road transport and in the organisation of winter wheat cultivation has a great impact on the final cost of grain and on the guaranteed food security of the Russian Federation. Research in this direction is currently relevant.

Currently, there is a high need to determine the shortest distances to form freight and passenger transportation routes. One of the most effective ways to determine routes of minimum length are methods of finding the shortest distances in a graph. The article discusses algorithms for finding shortest distances, as well as other methods based on the principles of their operation. It was conducted a comparative analysis to identify the advantages and disadvantages of using these methods in routing tasks.