Agroclimatic zoning of off-season (safrinha) corn for the first ten days of February in Goiás, Brazil

Through maps, agroclimatic zoning can help us understand the guidelines for the most suitable locations for sowing, minimizing risks of produce loss due to climatic adversities. The aim of the present study is to develop an agroclimatic zoning for the cultivation of a non-irrigated off-season (safrinha) corn in the state of Goiás, sown in the first ten days of February. The methodological steps were the delimitation of the representative bands of the climatic requirements for the crop; the spatialization of the climatic elements in the region; the spatial reclassification of climatic elements based on the climatic requirements for the crop; elaboration of the agroclimatic zoning map. Average, minimum, and maximum air temperature, accumulated precipitation, actual crop evapotranspiration and relative humidity of the air registered between February and July for the years 2013 to 2017 were used. The most suitable areas for the cultivation of the non-irrigated off-season corn sown in the first ten days of February in Goiás established by the agroclimatic zoning are concentrated in the South-Southwest and Northwest regions. The expressive presence of Latosol soil class and the proximity of the values of the climatic elements accumulated precipitation, temperature and altitude, which are proper for the development of the off-season corn, favour suitability of the areas.


Introduction
Agroclimatic zoning is a useful tool for technicians and farmers. Made available through a map, it facilitates the understanding of the guidance as to the most suitable locations to cultivate plant species, minimizing risks of produce loss due to climatic adversities (LANDAU et al., 2013). It is important to note that agroclimatic zoning does not include cultivation in areas of mandatory preservation, in accordance with Law No. 12.727 of 2012 (new Brazilian Forest Code).
The cultivation of agricultural species depends on their adaptation to edaphoclimatic conditions; it is necessary that the climatic components are similar to the places of origin of the plants -or the places where they have been genetically improved -according to the requirements of the species, this being the basis of the agroclimatic zoning (LANDAU et al., 2013;FRITZSONS et al., 2016).
A consensus among technicians and farmers, the season for sowing the off-season corn in the state of Goiás, associated with lower climatic risks and high yields, is the first ten days of February. This is because early sowing allows the plant to "escape" from water deficit in phenological stages, such as flowering and grain filling; the period also presents lower values of accumulated precipitation, which is important to the complete developmental cycle of the corn (HEINEMANN et al., 2009). Still, late sowing causes an expressive part of the plant cycle to be contemplated by higher temperatures, interfering with physiological aspects of the plant such as photorespiration and respiration (MAREN-CO;LOPES, 2013).
The objective of the present study was an agroclimatic zoning for the cultivation of non-irrigated off-season corn in Goiás sown in the first ten days of February.

Material and methods
The attributes necessary for rasterization to obtain maps were: average, minimum and maximum temperatures, relative air humidity, actual evapotranspiration and accumulated precipitation (climatic data), soil classes, altitude and terrain slope.
To make the agroclimatic zoning map, it was necessary to convert vector data into a matrix format, which enabled the development of map algebra operations through the computational application ArcGIS 10.1, in its kriging function. The system of geographic coordinates and cartographic projection used were Latitude/Longitude and SIRGAS 2000 (Datum), respectively.
The methodological steps used in the elaboration of an agroclimatic zoning start with the delimitation of the representative bands of the climatic requirements of the culture, spatialization of the climatic elements of the region, spatial reclassification of the climatic elements of the region based on the climatic requirements of the culture and elaboration of the map of agroclimatic zoning, delimiting the areas where there is agreement or not, or restrictions between the climatic requirements of the culture and the permissible limits of the climatic indices for that culture (SANTOS et al., 2015).
The climatic data come from the historical series of the National Institute of Meteorology from the automatic meteorological stations located in the state of Goiás, considering the first ten days of February between 2013 and 2017.
For each climatic element in each automatic meteorological station, the monthly average was obtained between the months of February and July -the period of cultivation of the off-season corn in Goiás -subsequently, through the monthly average, it was estimated the average for the period between the years 2013 and 2017. Thus, each automatic meteorological station (FIGURE 1) contained an average period value for each climatic element, forming a sample grid to produce isoline maps using the kriging model. The altitude and slope maps of the state of Goiás were obtained from the generation of the digital terrain elevation model produced by the active sensors Shuttle Radar Topography Mission. From those vector data, the numerical model of rasterized terrain is generated to produce the altitude and slope map. The digital soil class map was made available in the computational extension shapfile by the State System of Geoinformation of Goiás, on a scale of 1:100,000.
Initially, using the computational application ArcGIS 10.1, a climate zoning map was created for the non-irrigated offseason corn crop in the first ten days of February in the state of Goiás. To do so, based on vector data, maps were made in raster format of the climatic elements mentioned, which were reclassified (Arc GIS 10.1 reclassify function) according to the classes and coefficients described in Tables 1, 2, 3, 4, 5 and 6.   (2000).   (2000).  (2015). Using reclassified and rasterized maps of climatic elements and the raster calculator function of the Arc GIS 10.1 by the algebraic model: (accumulated precipitation x weight 40) + (average temperature x weight 30) + (actual evapotranspiration x weight 10) + (relative humidity x weight 10) + (minimum temp x weight 5) + (maximum temp x weight 5), a rasterized map was created, which was reclassified according to Table 7, generating the climate zoning map (FIGURE 2).

Range of climatic conditions
Coeffi cients

Suitable 10
Suitable with some climate restriction 8 Restricted 5 Very restricted 3 Unsuitable 1 Source: Elaborated by the authors (2020).
Also, rasterized maps (FIGURE 2) of the numerical terrain model (MNT), soil classes and slope were obtained, which were reclassified according to classes and the coefficients described in Tables  8, 9 and 10. According to EMBRAPA (2018, a and b), higher corn grain yields are obtained at altitudes above 700.0 m. Source: Elaborated by the authors (2020).   Finally, the reclassified maps of soil classes, slope, MNT and climate zoning were interposed using the Arc GIS 10.1 raster calculator function, with the algebraic model: (soil class x weight 50) + (climatic zoning x weight 30) + (MNT x weight 10) + (slope x weight 10). Suitable, intermediate, and unsuitable classes were inserted in the rasterized map of the interposition.

Results and discussion
The South-Southwest region and parts of the Northwest region concentrate the largest portions of the most suitable areas of zoning, followed by the Southeastern Goiás (FIGURE 3). The Northeastern region concentrates less suitable or even unsuitable areas. The South-Southwest and Northwest regions were possibly the most suitable (FIGURE 3) in the present agroclimatic zoning, due to the presence of the class of Latosol soils and favorable climatic conditions for the cultivation of corn, with average temperatures (25ºC) and accumulated precipitation in the period studied (600 mm) close to those ideal for the cultivation of "safrinha" corn. This possibility is sustained since the soil classes and climatic zoning had "weights" of 50% and 30% respectively in the construction of the present agroclimatic zoning.
In the Northeast region, containing less suitable or unsuitable areas (FIGURE 3), classes of Plinthosol, Gleysol and Neosol soils are present, as well as accumulated precipitation values below the reference values (600 mm) and higher maximum temperatures, but not above the maximum for the 35ºC culture, than those observed in the South-Southwest and Northwest regions, which classifies it as "restricted" in the climate zoning map (FIGURE 2).
By comparing the Southwest and South with the Northwest and North, we observe that the temperature variation cited in the previous paragraph is influenced by altitude (FRITZSONS et al., 2016), which was reported by Nimer (1979), who attributed to the latitude the higher temperatures in the North (24°C) and the lower temperatures in the South (22°C), while the relief favours higher average temperatures close to 22°C in places of lower altitudes, decreasing to 20°C in higher areas. This spatial variability was also found by Marcuzzo and Faria (2012) who, when spatializing the average annual temperature of the state of Goiás and the Federal District, observed annual averages between 26°C and 27°C in the Northwest (lower latitude and altitude) compared to Southeast and East (highest latitude and altitude) with values between 20°C and 22°C.
In 2005, Ribeiro et al. (2005) already observed that Goiás, especially in the Southwestern region, presents soil and climate conditions highly favorable to grain production, with a high percentage of soils with medium to clayey texture occurring in large plains and plateaus, and concentrated precipitation from September to May. Furthermore, the authors stated that like any agricultural production system, the off-season system would undergo transformations over the years.
Naturally, uninterrupted research programs on new systems for off-season corn cropping and genetic improvement make it possible to grow plants in locations previously considered unsuitable. Also, climate changes can alter the agroclimatic zoning in terms of the location and performance of plants in productive terms. Minuzzi and Lopes (2015), studying future climatic scenarios for growing off-season corn in the Midwest of Brazil, identified that there will be a reduction in the cycle duration of the plant because it is based on the concept of accumulated degree days. Thus, as the projections suggested an increase in temperature, sooner the crop of off-season corn will reach its energy requirement to complete its cycle. The reductions in the cycle for off-season corn for the Midwest are two to eight days in the short term (2016-2035) and six to eleven days in the medium term (2046)(2047)(2048)(2049)(2050)(2051)(2052)(2053)(2054)(2055)(2056)(2057)(2058)(2059)(2060)(2061)(2062)(2063)(2064)(2065). For the South of Goiás, represented in the study of the authors mentioned, in the municipality of Rio Verde, there will be, in the short term, reductions in the cycle and productivity in the order of 11 days and 0.802 t ha -1 , respectively. For the short-term scenario, the values are 16 days and 0.937 t ha -1 .

Conclusion
The most suitable areas for the cultivation of the non-irrigated off-season (safrinha) corn sown in the first ten days of February in Goiás established by the agroclimatic zoning are concentrated in the South-Southwest and Northwest regions. The expressive presence of Latosol soil class and the proximity of the values of the climatic elements accumulated precipitation, temperature, and altitude, which are proper for the development of the off-season corn, favour the suitability of the areas.