The distribution of crops in the world depends on climatic conditions. Since sowing, the plants are subjected to asynchronous variations of climate elements. These elements are critical factor which determine the probability of success of a crop cultivation [18] [19] [20] [21].

The crop requirements are normally described by agroclimatic ranges and are usually reported by species and even by genotype. The resulted potential areas will depend on the agroclimatic intervals considered in the diagnosis; if real optimal values are taken in to account, then, consequently, the best yields and economic profitability of the crop will be reflected.

Based on the reviewed information to determine the potential areas for S. bicolor, under irrigation conditions; it was considered high potential areas where all variables interact favorably for best crop development whilst in the suboptimal conditions the climatic and edaphological factors interact properly but with some limitations; and finally the unsuitable areas where all factors are constraining ones for crop development. Sorghum requirements were determined by consulting the bibliography, databases and expert knowledge.

The soil type (texture, depth, pH, drainage), average annual temperature, altitudes and slopes, among others (Table 1) were the factors considered to regionalize the different potential production areas.

Source: Own elaboration based on consultation of experts and different sources of information.

To process and analyze the information, the QGIS version 3.6 software was used [22]. This is a program created by Gary Sherman with the name of Quantum GIS in 2002; it was incubated by OSGeo in 2007 and in 2009 version 1.0 was launched. All QGIS activity takes place within the project which is a collection of associated manageable documents during the session. Projects can contain five types of documents: views, tables, charts, layouts (or printed outputs), and scripts. The corresponding file format is *.qgs.

The project is formed by particular configurations saved in a data frame. The system can also accept: the coordinate reference system, the composition of the layers, the symbology of the layers, the configuration of the system and the network. The QGIS also ensures that the map layers are displayed in the correct coordinate reference system (provided the first settings are correct).

In this work, vector maps *.shp were used in which geoprocesses of cuts, dissolutions, unions and intersections were carried out. Once reclassified, based on crop requirements, the intersection of the variables was computerized in order to generate and de-limit optimal, suboptimal and unsuitable potential areas (Figure 1). Maps were generated through cartographic intersections between polygons, and potential classes were also defined. As a result, the final map, based on the inter-sections, provided in-formation about potential growing areas.

Sweet sorghum can be cultivated in large parts of the Mexican Republic; however, there is a great affinity for the coasts, especially in the Gulf of Mexico (Figure 2). This plant develops well in warm climate conditions, with moderate and well distributed rains according to Pérez, 2010 [23]; the ideal temperature should be above 18˚C in order to germinate and grow properly [24].

The optimal growth temperature is from 26.7˚C to 29.4˚C. Temperatures above 38˚C are harmful, despite the fact that this plant tolerates heat and drought better than corn [25]. Other authors such as Acuña et al., (2002) [26], suggest good temperatures for sweet corn of 24˚C to 30˚C. During the germination phase, it needs temperatures of 12˚C to 13˚C, therefore, temperatures below these are considered unsuitable; growth is activated above 15˚C, with the optimum around 32˚C [27]. When temperature decreases, during flowering, grain yield can be reduced; sterility of the spikelets and pollen grain viability is also affected [28]. On the other hand, very high temperatures (greater than 38˚C), after flowering, reduce the final weight of the grain and cause abortion of flowers [23]. By instance, it has been suggested that 27˚C, is the optimal temperature; being 21˚C the minimum temperature for good growth [29].

At the national level, sorghum is produced under both irrigation and rainfed conditions. During the 2012-2016 period, 35.5% of the total sorghum area was harvested under irrigation conditions, producing 47.3% of the total production with an average yield of 4.9 Mg∙ha⁻¹, while 64.5% of the total surface harvested was cultivated under rainfed conditions producing 52.7% of the total production with an average yield of 3 Mg∙ha⁻¹ [30].

Sweet sorghum adapts to different humidity conditions, so rainwater is sufficient to complete its vegetative cycle, especially in the sub-humid tropics [31], where rainfall ranged between 700 and 1600 mm per year. However, additional water by irrigation is needed in areas where the rainfall distribution is erratic and less than 700 mm per year. Provided water is important especially in the emergency stages, vegetative development, stem and spikelet formation according to studies carried out by INIFAP, in the Experimental Field Station of Valle de Mexicali [32]. When necessary it is recommended to apply 10 cm of water before sowing. Two supply irrigations should be added, with 20 cm each; the first at 40 days after sowing and the second at 65 - 70 days after planting [17] [33].

Due to its high temperature requirements, sweet sorghum is rarely cultivated beyond 1800 m high; however, in the African continent it is cultivated between 400 m and 2500 m altitude [34]. In the American continent, it adapts to an altitude ranging between 20 and 850 meters above sea level [35] considered as optimal for its development. It has been suggested that this plant can grow from 0 to 1500 meters above sea level [23]. It is common to find good areas close to water bodies, with low elevation, and favorable warm and humid climate. In Mexico, the optimal and suboptimal altitude for sweet sorghum is shown in Figure 3.

The best soils for Sorghum bicolor (L.) are those of high fertility, sandy, loamy or clayey texture [23] [35]. Sweet sorghum prefers deep soils, without excess salts, with good drainage, without hardened layers. It is moderately tolerant to soils with some salinity and/or alkalinity. According to studies the presence of calcium carbonate in the soil increases the content of sucrose in the stem and leaves [36] [37] [38] [39]. It grows better, under salinity conditions, than other crops such as wheat, soybeans and corn.

The soils must have good drainage, since excessive humidity affects the normal development of the plants. The edaphic requirements of the crop [25] [35] [40] are classified as: Fluvisols, Regosols, Luvisols, Nitisols, Andosols, Phaeozam and Kastañozem among others. These soils have a depth greater than 50 cm, with good moisture retention and very porous. In Mexico, the distribution of optimal and suboptimal soils is being shown in Figure 4.

It is considered that 0 to 16% is the optimal slope range for good crop development [41], and 16% to 20% as a sub-optimum one. Naidu et al., (2006) [42] assures that soil inclination should be less than 16% when the purpose is to produce the greatest amount of biomass for sugar production. Mexico is a country characterized by having a significant surface area with slopes between 0 and 16%; while in contrast, slopes of 16% - 20% are mainly found in the mountain ranges of the country (Figure 5).

Sweet sorghum grows well in soils with pH ranging between 5.5 and 8.5; however, the ideal pH is between 5.5 and 6.5 [23] [43]. It supports salt and it is suggested that sugary varieties require the presence of calcium carbonate in the soil, which increases the sucrose content of the stems and leaves [23].

The environment plays an important role in sugar production [44]. Reports indicate that sweet sorghum is very efficient to produce sugar in warm environments [45] [46] with high light intensity [45]. However, it is considered a short day crop (<12 hours), although there are neutral day cultivars [47]. Panicle formation and flowering accelerates in short days while delaying in long days [48].

Sorghum bicolor L. Moench is one of the oldest crops and currently one of the most important cereals in the world [49]. It grows well in all continents, in tropical, subtropical and temperate regions; in lands of medium and low agricultural aptitude, and especially suitable for regions with little precipitation [50]. Sorghum can be cultivated in large parts of the Mexican Republic; however, the best region is located in the coasts, especially in the Gulf of Mexico, where soils such as Cambisol and Vertisol type are the most common. On the other hand, it is suggested that Tamaulipas and Guanajuato are the best states (Figure 6, Table 2) where sorghum can be produced with better yields under irrigation; a practice that is currently carried out intensively.