PLANT ARRANGEMENT AND NITROGEN FERTILIZATION IN GRAIN SORGHUM PRODUCTION

– The appropriate arrangement of sorghum plants combined with the supply of nutrients increases grain yield. In this context, the objective was to evaluate the agronomic performance of grain sorghum grown under different plant arrangements and nitrogen fertilization levels. Experiments were carried out in Rio Verde and Montividiu in a 3 x 2 factorial randomized completely block design with six replications, with three spacing between rows (reduced, traditional and double row) and the use or not of 90 kg ha -1 topdressing nitrogen. There was a beneficial effect of topdressing nitrogen fertilization on grain yield when sorghum was grown in double rows in both locations, and for the reduced arrangement in Montividiu. However, the effect of topdressing nitrogen fertilization on grain yield in the traditional arrangement was not found. The dry shoot biomass of sorghum plants increased with nitrogen fertilization in Montividiu. The arrangement or topdressing nitrogen fertilization did not influence the thousand-grain weight of Sorghum.


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The grain sorghum acreage in Brazil for the 2021/2022 growing season is estimated at 865 thousand hectares, in which the state of Goiás is the largest producer of this cereal among the Brazilian states (46% national production) (Acompanhamento da Safra Brasileira de Grãos, 2022). In this context, the growing demand for sorghum grain by agroindustries installed in Central-West Brazil was a significant factor in the consolidation of the crop in the region (Silva et al., 2015).

Almost all sorghum grain production in the
Cerrado is made in the off-season. This type of cultivation is characterized by planting sorghum after harvesting another plant species in the summer crop, usually soybeans. In this region, Sorghum is primarily planted between the second half of February and the first half of March. Therefore, the sowing of the crop may occur later when the expected rainfall volume is not enough to meet the water needs for corn cultivation (Menezes, 2015). Due to the lower water requirement concerning this crop, sorghum has been considered a versatile crop, with a high capacity to adapt to different climatic conditions and support periods of drought (Mahmood & Honermeier, 2012).
In addition, these traits allow sorghum to grow under limited rainfall conditions for other plant species, such as corn.
Despite the high adaptability of the crop in Brazil, Sorghum's estimated average grain yield of Sorghum for the 2021/22 growing season was 2,856 kg ha -1 (Acompanhamento da Safra Brasileira de Grãos, 2022). This value is considered very low for the productive potential of the crop. In addition, factors such as the lack of specific Phyto technical adjustments for the primary hybrids or varieties available on the market, inefficient weed control, and the absence or insufficient fertilization for the crop may justify the low grain yield of sorghum found in Brazilian crops.

The availability of sorghum hybrids in the
Brazilian market has grown significantly over the years. However, genotypes with different plant architecture traits, such as height, morphology, leaf angle, cycle, and production potential, cannot have a single recommendation for cultivation with Phyto technical management. Therefore, specific adjustments are required, considering regional aspects, such as soil and climate. In this sense, one possibility to maximize agricultural crop productivity is using different plant arrangements instead of those traditionally adopted. The definition of the ideal plant arrangement makes it possible for sorghum to be more efficient in capturing solar radiation and exploiting the water and nutrients in the soil (Albuquerque et al., 2010). Gradual reductions in row spacing in offseason crops have been occurring over the years in Brazil to facilitate the implementation of both crops.
For sorghum, higher grain yields were obtained with 0.45 cm row spacing, compared to 0.60 and 0.90 m (Bishnoi et al., 1990).
Still, concerning the factors limiting the crop grain yield, differently from what has been advocated, the rusticity associated with sorghum does not mean that this plant species do not need nutrients or even does not respond to fertilization in general (Goes et al., 2011;Borges et al., 2016). Traditionally, the nutrition of sorghum plants derives from the use of residues from fertilization made in summer crops, such as soybeans, or even from the release of nutrients from the decomposition of crop residues.
Despite this, sorghum may have a high nutritional requirement, especially when seeking high grain yield levels (Borges et al., 2016).
One of the primary nutrients required by sorghum is nitrogen, which accumulates in plants until maturity (Goes et al., 2011;Mateus et al., 2011). However, despite the great demand for this macronutrient, using nitrogen fertilization in topdressing is not common practice in cultivating grain sorghum in the off-season (Goes et al., 2011).
This situation occurs because producers sometimes do not want to increase the crop cost production and because responses to topdressing fertilization are variable. These parameters are mainly conditioned to the genetic material, the expected yield, the soil organic matter content, and soil water availability (Mateus et al., 2011). Thus, adjustments in row spacing, respecting the cultivar's particularities, and using nitrogen fertilization can increase sorghum grain yield. Furthermore, this circumstance would bring additional benefits, such as helping to suppress the weed community, as the crop may have a superior competitive ability concerning weeds (Bishnoi et al., 1990;Braz et al., 2019).
In this sense, the objective of this study was to evaluate the agronomic performance of grain sorghum grown in different plant arrangements, as well as the response to topdressing nitrogen fertilization in crops grown after soybeans.

Material and Methods
Two field experiments were conducted in the state of Goiás; in the municipalities of Rio Verde  ) and the apparent harvest index (ratio of the grain weight, with grain moisture corrected, to the total shoot dry biomass).
Statistical analysis was performed separately for each experiment. Data were tested by analysis of variance by F-test, using Tukey's test (p≤0.05) when significance was detected for the factors tested or for the levels of each factor.

Results and Discussion
The results showed the interaction of plant arrangement with nitrogen fertilization for plant height in both locations (Table 1) Without nitrogen, no differences were detected in the height of sorghum plants.
Still, in the same municipality, nitrogen fertilization in the traditional plant arrangement allowed for increases in plant height of more than 10 cm compared to the management without fertilization (Table 1)   Similarly, in Rio Verde, nitrogen fertilization did not influence panicle length when sorghum was grown in reduced spacing arrangements with a higher plant population and double row spacing (Table 3).
Nevertheless, nitrogen fertilization in the traditional plant arrangement reduced the length of sorghum panicles.
In Montividiu, there were no differences between plant arrangements for panicle length when nitrogen was supplied as topdressing (Table   3) The beneficial effects of topdressing nitrogen on sorghum can be observed by the increase in the plant  (Table   4). However, plant arrangements did not promote changes in the sorghum shoot dry biomass in both locations. Importantly, with a dry biomass production of approximately 20,000 kg ha -1 of the grain sorghum hybrid BRS 330, grown after soybean, it represents an exciting option for straw production for the notill system, as highlighted by Rossi et al. (2013) for the same locality. Furthermore, sorghum biomass produced after soybean becomes an alternative for animal feed in integrated crop-livestock systems in the Cerrado (Oliveira et al., 2020a(Oliveira et al., , 2020bSantos et al., 2020;Sousa Júnior et al., 2020).

Sorghum grain yield was influenced by
the interaction of plant arrangement and nitrogen fertilization in both locations (Table 5). For example, in Rio Verde, nitrogen topdressing in the traditional and double-row spacing arrangements provided higher grain yields than the reduced arrangement, with values above 5,000 kg ha -1 . However, when nitrogen fertilization was not carried out in this location, the traditional plant arrangement resulted in a higher grain yield than obtained in the double-row spacing arrangement, not differing from the value obtained in the reduced spacing arrangement with a Mean values followed by different lowercases, in the same column, and uppercases, in the same row, are significantly different by Tukey's test at 5% probability.
higher plant population.
Also, in Rio Verde, topdressing nitrogen fertilization in double-row spacing increased grain yield by greater than 1,500 kg ha -1 . In the other arrangements, no effects of topdressing fertilization on sorghum grain yield were observed. The absence of responses to nitrogen fertilization in the plant arrangements mentioned above may be because sorghum was grown after soybeans. In this condition, soybean straw decomposition contributed to the supply of nitrogen to sorghum, as observed in the cultivation of corn after soybean (Duarte, 2013). It is important to recall that topdressing was carried out in early April when there was no water deficit ( Figure   1), which favors the increase in nitrogen uptake.   It is essential to highlight that the variation in sorghum grain yield observed between treatments is a function of the interaction of the crop and environmental factors. Adopting hybrids in a given population of plants and row spacing is essential to increase grain yield and financial return to producers (Fromme et al., 2012). The ideal population of grain sorghum plants can differ between cultivation environments, especially when evaluating environments with high potential and those with restrictions to obtaining high yields (Staggenborg et al., 1999). Since the agricultural areas of Montividiu are located at higher altitudes than those of Rio Verde, there is a more favorable environment for obtaining higher sorghum grains after soybeans, as suggested by Silva et al. (2015). In analyzing the apparent harvest index of the sorghum crop, the plant arrangements did not influence this variable in Montividiu, regardless of nitrogen fertilization (average value of 25%) (  Sorghum's response to nitrogen fertilization is strictly related to productive potential and the species previously grown, in addition to the sowing time of Sorghum in succession. Therefore, planting this cereal later due to a delay in soybean harvest, which did not occur in the present study, is advisable not to use topdressing fertilization for hybrids with morphophysiological traits similar to BRS 330.
This choice is because water restriction during the vegetative development of sorghum limits nitrogen uptake and, consequently, higher grain yields.
In this context, due to the results of the studied hybrid, when the conventional plant arrangement is adopted, it becomes more interesting not to apply nitrogen fertilization. In addition to providing greater In environments more favorable for obtaining higher grain yields (Montividiu), the topdressing fertilization in grain sorghum favors increasing sorghum shoot dry biomass.