Sorghum culture initial establishment based on sowing machines working speed and furrowing mechanisms

The main goal of this article was to evaluate, at field conditions, the performance of a seeder-fertilizer in the initial establishment and the sorghum culture productivity according to tractor working speed and seed deposition depth. This study was conducted at the Experimental Farm in São Gonçalo dos Campos, located in the municipality of São Gonçalo dos Campos, BA, which belongs to the Veterinarian Medicine and Animal Science School of the Federal University of Bahia UFBA. It was adopted factorial scheme methodology 3x3 in CDR (Completely Randomized Design) or Dic (Delineamento Inteiramente Casualizado) in Portuguese, with 36 experimental unities with three displacement speed (4, 6, and 8 km h-1), and three sowing deposition depths (0.01, 0.03 and 0.05 m). The real seed deposition, the Plant Height at 30, 60, and 90 days, as well as the productivity per m2 after 90 days, were assessed. The working speed did not influence (P&gt; 0.05) the evaluated parameters. The sowing depth did not change (P&gt; 0.05) the crop productivity; however, it did influence the actual seeds deposition and the plants height on the first two cuts. Sowing at speeds from 4 to 8 km h-1 and planting from 0.01 to 0.05 m depths do not influence the sorghum crop productivity. Thus, it is recommended to carry out planting at a speed of 8 km h-1 with a depth of 0.05 m.


Introduction
Due to its rusticity, sorghum stands out in arid and semi-arid regions, achieving good biomass productivity and showing tolerance to water deficit (TOLENTINO et al., 2016 (CONAB, 2020). Among the various types of sorghum grown in Brazil, forage sorghum is the one which shows the prominent growth in new areas of the country (SILVA et al., 2020).
Sowing quality, alongside several other factors, may impact Sorghum productivity. Thus, this is one of the agricultural operations which requires a lot of attention and control. The performance of the sowing operation must be proper and under suitable quality control (CARPES et al., 2018).
For the process, the sowing machine must be regulated according to type soil, preparation, density, and texture. Incorrect adequacy may lead to problems in the deposition of seed and fertilizer, in the emergence of seedlings, and consequently, the final crop productivity will be affected (MACEDO et al., 2016).
For Garcia et al. (2011), another major factor to be dealt with in mechanized seeding process is the operating speed of tractor/seeder set, which may influence the sliding of the wheels, the operational capacity, the dosage of seeds and fertilizers, the distance between seeds as well as the depth and seed exposure.
Working during sowing at speeds above the recommended can increase the number of failures and double seeds, which will impair the uniformity in seed distribution. Working under low speed, the time for sowing is increased significantly. Such factors may reduce the plant population and increase the number of competing plants (BELLÉ et al., 2018). Carpes et al. (2016) described a tendency to reduce the level of machine precision by angular speed increase of seed dosing disk. Similarly, Jasper et al. (2011) observed that the reduction of acceptable spacing is associated with angular speed increase of dosing disk pneumatic mechanisms, when analyzing the influence of sowing speed (speeds of 4; 6; 8; 10 and 12 km h-1) on the longitudinal distribution of soybean seeds.
It is necessary to emphasize that the significant demands for power will occur at the highest operation speeds and seed deposition depth, once the demand for power has a direct relationship between traction force, speed, and worked area. The sowing depth is an important factor relevant to its seed germination (Oliveira & Scivittaro, 2007). It may vary according to the cultures to be worked with. Proper sowing needs to be carried out at a depth enough for the plant to obtain nutrients more easily and to assist the plant's sustainability. Thereby, fast, and uniform germination occurs, spending fewer energy reserves. (Shanmuganathan & Benjamin, 1992).
The usage of inadequate speeds and adjustments in mechanized sowing can provide uneven seed distribution in the row; plants remarkably close to each other will cause competition, inhibiting their development, greater lengths of the hypocotyl, and negative effects on crop productivity. (MONDO et al., 2013). Correia et al. (2015) stated that the sorghum sowing period is short according to the edaphoclimatic conditions and the economic situation of the crop. Thus, operations must be carried out as quickly as possible, being necessary to increase the speed of the tractor-seeder-fertilizer set. This increase is one of the main factors which negatively affect the sowing quality. The authors comment that the sowing-fertilizers have undergone modifications to improve the efficiency of longitudinal distribution between seeds and, therefore, positively influence the crops productivity.
Hence, the objective of this study was to evaluate, at field conditions, the effects of working speed and seed deposition depth on the initial establishment as well as productivity of the sorghum crop.

Methods and material
The study was carried out at the experimental farm of the Federal University of Bahia, located in the municipality of São Gonçalo dos The seeder-fertilizer was adjusted to 0.60 m spacing between lines and stand of 150,000 plants per hectare, sowing six lines. The first and sixth lines were removed, obtaining data from lines 2, 3, 4, and 5 (central lines), from now on renamed lines 1, 2, 3 and 4. Two meters were disregarded at the beginning and at the end of each sowing line to stabilize the speed of the mechanized set in the data collection.
The parameter analyzed to check the sowing quality was the seed deposition actual depth. Productivity was verified in each treatment using following parameters: (1) productivity per hectare and (2)  First, the assumptions of data normality were analyzed. The data with normal distribution were performed by variance analysis and, when significant, the data were performed to regression analysis for all parameters. The complete linear and quadratic models were tested. In case of significant interactions for the factors, the respective developments were carried out. All analyses were performed using the statistical software SAS 9.2 Student at 5% significance level.

Discussion and results
The real seed deposition depth was not influenced by the displacement speed. However, there was an effect of sowing depth and interaction of the factors studied under this characteristic. As to produce dry matter, there was no influence of the studied factors or their interactions.
Longui, Leite, Oliveira, Moraes, Santos, Souza Sorghum culture initial establishment based on… The actual seed deposition depth was influenced by sowing regulation, which shows that the machine system worked as expected ( Figure 1). The averages for those treatments demonstrated the numbers are close to regulation. For Pinto et al. (2017), studying the longitudinal spacing and productivity of cowpea using a manual seeder, stated that the manual seeder at speeds from 2 to 4 km h-1 influences the depth of seed deposition, with effects on the initial and final crop populations.
The sowing speed influence on the seed deposition actual depth is quite favorable to the producer. Thus, the producer may adopt any speeds between 4 to 8 km h-1. However, at higher speeds, the tractor-seeder-fertilizer set will have a greater operational capacity, reducing the hours worked in the seeding and, consequently, reducing the final costs.
The planting speed and seed deposition regulation did not influence the final crop yield, which showed values between 53 to 56 tons per hectare of DM. These production levels are in accordance with those reported by Rodrigues Filho et al. (2006).
Our results were different from those found by Reynaldo et al. (2016). Evaluating the influence of displacement speed in the soybean culture sowing operation, using a fertilizer sowing machine with a mechanical seed distribution system by horizontal discs, they verified a reduction in productivity from 3550 to 3450 kg ha-1 of grains, when the speed was increased from 2 to 10 km-1. Rinaldi et al. (2013) also observed that speed increase provided higher values of flawed spacing in the bean culture, which can contribute to plants number reduction and, therefore, the culture productivity.
The plant height was influenced by sowing depth at 30 and 60 days, which did not occur at 90 days. The seeds deposited more superficially emerged and developed first. Over time, the deeper seeds matched the growth with those sown more superficially. Figure 2 shows the equations, describing this response pattern. This phenomenon is noticeable at the beginning of growth, due to the smallest soil strip that must break from germination to emergence. However, over time, the height of plants tends to match, as the deeper seeds may explore a larger volume of soil, which allows for greater support and nutrition (SOUZA e FERNANDES, 2006). Studies show that the seeds have an ideal range of sowing depth. If planted too deeply, they do not have enough energy to reach the surface. On the other hand, when they are shallow plants, there is no soil-seed contact, and the action of the sun accelerates their dryness (BIULCHI, 2012). Sorghum culture initial establishment based on… This result corroborates with the study developed by Teixeira et al. (2018) that studying different sowing depths in the corn crop, described differences in the initial periods of their study. However, they did not obtain this result in the last collection.