SOWING ARRANGEMENTS OF SORGHUM WITH BRACHIARIA FOR FORAGE PRODUCTION AND SOIL COVER

The objective of this study was to evaluate the dry matter content and morphological parameters of sorghum and brachiaria (signalgrass, specifically palisade grass) grown simultaneously for forage production, along with soil cover formation outside of the primary crop season. The treatments were in a randomized block design consisting of three different sowing arrangements: sorghum + two rows of brachiaria between sorghum rows, sorghum + two rows of brachiaria (one in the row + another between the sorghum rows), and sorghum with brachiaria broadcast; as well as sorghum and brachiaria in monoculture. In the first cycle, the dry matter yield of sorghum was higher, approximately 12.01 t ha-1, in the arrangement of sorghum alone. However, the highest total dry matter yield was obtained in the arrangement of sorghum with broadcast brachiaria, with 11.01 t ha-1 for sorghum and 3.75 t ha-1 for the brachiaria. In the second cycle, soil cover was greatest in the brachiaria monoculture and the arrangement of sorghum with broadcast brachiaria, at 95% and 86%, respectively. Therefore, intending to produce forage sorghum and form adequate soil cover by brachiaria, the sorghum intercropping with brachiaria in broadcast sowing is a promising strategy.

Traditionally, the forage sorghum is grown in the fallwinter and spring-summer seasons. However, most of its production is in the fall-winter and represents approximately 70% of the total sorghum produced in Brazil. The greater concentration of sorghum production in the fall-winter period results from the lower market value of sorghum compared to primary crops like maize and the greater hardiness of sorghum.
These features allow satisfactory yields even under adverse conditions. However, silage production systems involve considerable extraction of nutrients and soil exhaustion because the whole plant is harvested. Also, soil turnover and machine movement lead to high losses of soil and fertility (Freitas et al, 2005). The adoption of no-till planting (Moraes et al., 2016) may minimize this problem by reducing the eutrophication and water pollution besides improving the chemical-physical parameters of the soil through soil cover, crop rotation, nutrient cycling, organic matter preservation, and efficient use of inputs and machinery.
However, the no-till system implies the maintenance of soil cover as long as possible to delay the plant desiccation and to form the straw cover on the soil surface. Menezes et al. (2015) and Pascoaloto et al. (2017) claimed that the use of sorghum, maize, oats, and brachiaria grasses (fall-winter crops) integrated with a planned rotation system provides high potential for plant biomass production with a high C / N ratio, thus ensuring the minimum quantity to keep the soil covered longer. Therefore, aiming to produce the maximum amount of pasture biomass or a no-till system, the simultaneous growth of two or more fall-winter crops may be most appropriate.
Supporting this assertion, several authors have found a high plant biomass production in simultaneous growth of sorghum and brachiaria grasses (Borghi et al., 2013;Neto et al., 2014;Ribeiro et al., 2015). Furthermore, Neto et al. (2014) stated that the plant regrowth of brachiaria growing simultaneously with sorghum proved to be a viable technique for forage production and soil cover in the off-season in the Brazilian cerrado (tropical savanna) conditions.
Various studies have discussed the advantages of simultaneous cultivation of sorghum and brachiaria grasses.
However, according to Neto et al. (2014), few studies have considered the most suitable sowing arrangement to prevent competition between both species, especially the reduction of sorghum yield.
Furthermore, there are no graminicides to stall the growth of brachiaria competing with the sorghum crop. In addition, another gap observed in this area is the absence of studies monitoring the pasture formation and vegetative matter production of regrowth followed by straw cover after sorghum harvest. In addition, no studies address the sorghum growing with broadcast sowing of brachiaria. Thus, this study aimed to evaluate arrangements of sowing forage sorghum with brachiaria aiming at sorghum silage production and the formation of soil cover for no-till planting.

Materials and Methods
The experiment was set up considering the fall-  Figure 1.

The soil is classified as Argissolo Vermelho
Amarelo (Santos et al, 2018 Astral, a hybrid intended for silage production, with an early cycle. The brachiaria sown was Urochloa brizantha cv Marandu, a perennial vegetative cycle cultivar that grows in clumps. After germination tests made in pots, the pelletized seeds with high purity (around 95%) were used. In the MB, SBB, and SBBR plots, the seeds of brachiaria were sown at a density of 32 g. In the SBBc plots, the sowing density was 48 g to minimize germination and emergence failure due to greater seed exposure to biotic and abiotic factors.
Fertilization at planting was performed using 300 kg ha -1 of the formulation 8-28-18 of N-P-K, following the soil analysis results.
The fertilizer was applied only in the sorghum rows. The sorghum and brachiaria seeds were sown at a depth of 2 cm, as recommended by Freitas et al. (2005), except in the plots where brachiaria was broadcast. Fertilizer was broadcast in top dressing 25 days after sorghum emergence using 140 kg ha -1 of ammonium sulfate (Mateus et al., 2011 At the sorghum harvest, plants of brachiaria were sampled to determine the brachiaria population in the sorghum field. Two random 0.25 m 2 were taken in each plot (Freitas et al., 2005). Regression analysis was also performed to observe the response of total dry matter in regrowth over time during the second evaluation cycle. The regression models were chosen based on the significance of the regression coefficients using the t-test at 5% probability, the coefficient of determination (R2), and the biological phenomenon.
The Sisvar and Sigmaplot 11 packages were used to perform the analyses indicated.

Results and Discussion
The results for the means test for the  According to Freitas et al. (2005), this occurs due to broadcasting brachiaria without incorporating the seeds in the soil, augmenting the chance for sorghum to germinate, emerge, and be established.
In the case of the SBB arrangement, the presence of brachiaria only between the sorghum rows and the rapid establishment of the sorghum allowed greater initial use of resources and accumulation of reserve substances, resulting in lower reductions in dry matter yield (Silva et al., 2014). In the SBBR, however, the presence of brachiaria in the sorghum plant rows and between the plant rows resulted in greater interspecific competition for light, nutrients, and water. In addition, the experiment conducted in the fall-winter period (low light levels) worsened competition for light, which may have brought about a low photosynthetic rate.
Therefore, it was expected that the experiment performed in the fall-winter period would lead to a drastic reduction in dry matter yield since sorghum is a species with a C4 photosynthetic mechanism, which requires high light levels and high temperatures.
However, the drastic reduction did not occur. That is because the mean maximum temperature of 27°C and mean minimum temperature of 16°C observed ( Figure   1) were within the mean maximum and minimum limits of 36ºC and 16ºC, respectively, required for the growth and development of the crop (Magalhães et al., 2003). Moreover, although the accumulated rainfall of 315 mm observed during the experiment ( Figure 1) did not reach the 380 to 600 mm required by the crop (Sans et al., 2003), this water deficit was overcome by irrigation. June. Even so, the main objective was achieved in the first cycle. The establishment of the brachiaria in this period was essential in all the sowing arrangements.
The results for the partitioning of dry shoot matter are shown in Figure 2B. The proportions obtained in partitioning of dry matter for panicles, stems, and leaves were 39%, 56%, and 5% in MS; 37%, 57%, and 6% in SBB; 29%, 64%, and 7% in SBBR; and The results for the tiller parameter for the two forage crops and soil cover in the second evaluation cycle are shown in Table 2. The tillering of sorghum in regrowth was more significant in the MS and differed from the simultaneous growing in SBB, SBBR, MS -monoculture sorghum -Control 1; MB -monoculture brachiaria; SBB -sorghum + two rows of brachiaria between the sorghum plant rows; SBBR -sorghum with one row of brachiaria between the sorghum rows and another row of brachiaria in the sorghum plant row; SBBc -sorghum with broadcast brachiaria. The SBBc arrangement had a more significant number of brachiaria tillers in regrowth (767 tillers m -2 ) and differed statistically from the other sowing arrangements, as shown in Table 2. As the first cycle, tillering in SBBc was more significant than in MB, probably as a consequence of the greater sowing density in this arrangement, along with the excellent quality of both the brachiaria seeds and soil moisture conditions in the post-sowing period ( Figure   1), favoring the establishment of the seedlings.
Nevertheless, the tillers obtained in the SBBc arrangement had smaller diameter stems than those obtained in MB. Notably, there was compensation between the number of tillers and their stem diameter (Santos et al., 2011). At high population densities, the plants allocate their resources to more rapid growth to avoid shading, thus increasing the possibility of growth above the canopy, though this reduces the stem diameter (Rodrigues et al., 2018;Santos et al., 2011).
The other arrangements, SBBR and SBBc, had lower values for tillering, at 386 and 337, respectively. Once more, the SBBR arrangement had the lowest mean value, suggesting that there was a greater competition between sorghum and brachiaria when the brachiaria was planted in the sorghum row, resulting in the allocation of resources for the growth and development of the already existing tillers in detriment to the formation of new ones. There were significant differences for the soil cover parameter evaluated at 155 days after sorghum harvest ( Table   2). A more significant percentage for soil cover was obtained in the MB and SBBc arrangements, with 95% and 86% of the soil covered, respectively ( Table   2). The percentages of soil cover in the SBB and SBBR arrangements also did not differ from each other, at 53% and 60%, respectively (Table 2).
Notably, these indices were lower than those obtained in the MB and SBBc treatments. The MS arrangement had the lowest soil cover percentage at around 28%. The total soil cover achieved in the MB and SBBc arrangements is a consequence of the quality of the brachiaria seed, along with suitable temperature and rainfall conditions (Figure 1) observed near the end of the evaluation period, from September to November, which resulted in greater availability of resources for tiller growth and development (Timossi et al., 2007). In the SBB and SBBR arrangements, the partial cover obtained resulted from the greater competition between the sorghum and brachiaria in the first cycle, which resulted in less growth and development for both crops. Then, in the second cycle, even with improvement in climate conditions, the plant response of sorghum and brachiaria was slow.
Nevertheless, probably a more remarkable growth and development of brachiaria would occur if the evaluation had been prolonged until December.
In the MS arrangement, the lower soil cover was due to the absence of brachiaria and the lower growth and development of the sorghum regrowth. The sorghum regrowth achieves more or less 60% of the dry matter obtained in the first cutting (Botelho et al., 2010), which presumes drastic reductions in plant biomass production and soil cover capacity.
The results for sorghum and brachiaria dry matter in the second cycle are shown in Figure 3. The sowing arrangements differed regarding the dry matter yield of the sorghum. The MS arrangement exceeded the others, obtaining around 11.01 t ha -1 , which corresponds to 91% of the yield obtained in the first cutting, more significant than the 60% considered satisfactory by Botelho et al. (2010). In simultaneous growing of sorghum with brachiaria in the SBBc, SBB, and SBBR arrangements, there were reductions in dry matter yield in the order of 61%, 35.1%, and 17.5%, respectively, concerning the MS.
In the MS, the yield obtained is a consequence of the absence of interspecific competition in the row and between the rows, which increases the absorption efficiency of nutrients, light, and water (Albuquerque et al., 2011). Although there were reductions in the dry matter yield of sorghum in the second cycle, the levels obtained were satisfactory in the SBB and SBBR arrangements, which may be attributed to the topdressed fertilization performed at the beginning of this growing period. Together with that, improvement in climate conditions, with higher temperature and soil moisture from September to November ( Figure   1), favored the growth and development of the sorghum crop.
The forage sorghum with a C4 photosynthetic metabolism is considered a crop sensitive to photoperiod, requiring high temperatures and high light levels to develop fully (Magalhães et al., 2003).
However, the sorghum dry matter yield in the SBBc   Figure 4. This total dry matter accumulation had a quadratic response ( Figure 4). First, there was an increase in plant matter production. Then, from 140 DAC, the dry matter began to decline, probably due to the beginning of sorghum plant senescence.
More gains in sorghum dry matter are not expected from that point on. As senescence begins, there is a gradual reduction in leaf area, which is reflected in the reduction in the dry leaf matter, impacting the total dry matter in sorghum plants (Barbosa et al., 2019). The total dry matter had an increasing quadratic response in all the arrangements involving intercropping of sorghum with brachiaria (4C, D, and E). However, the highest increase rates in the dry matter were found at 140 DAC in the SBBc arrangement, with the accumulation of 14.02 t ha -1 , which is due to the combination of good yield indices for sorghum and brachiaria. This result was followed by SBBR (11.64 t ha -1 ), and the lowest value was for SBB (10.51 t ha -1 ). It should be highlighted that the total yield of plant biomass in simultaneous growing was more significant than the yields in the respective monocultures. The greater density of brachiaria leading to rapid colonization by the plants can explain the high indices of total dry matter accumulation in the SBBc arrangement. This results in greater use of light and nutrients, consequently, a more significant gain in plant biomass. (Costa et al., 2012;Timossi et al., 2007).
From the total dry matter accumulation, it can be inferred that the simultaneous growing of sorghum and brachiaria proved to be viable for forming pasture or forming soil cover for no-till planting. Regardless of the sowing arrangement, adequate plant biomass was formed both for pasture and desiccation and the formation of straw cover. All the treatments had dry matter yield greater than 6 t ha -1 , the amount recommended for forming adequate soil cover (Silva et al., 2014;Timossi., 2007).

Conclusions
Efficiency in production of sorghum forage in the 1st cycle and formation of pasture and/or soil