Beet production using vermiculite incorporated with Dystrophic Red Latosol ( Oxisol )

Vermiculite is an expansive material that can be used for crop production. However, information about the use of vermiculite in vegetable production is scarce. Thus, this study's objective was to evaluate the effects of vermiculite levels incorporated into the soil (Red Latosol Dystrophic) for beet (Beta vulgaris L.) crop production. The experiment was performed during spring using the beet cultivar 'Early Wonder Tall Top' and 0, 2, 4, 6, 8, and 10 t∙ha of vermiculite incorporated into the soil before seedling planting. The increase of the vermiculite doses caused a linear decrease of the fresh root and leaf weight. The yield reductions were due to the great water holding capacity of the vermiculite and the consequent high incidence of cercosporiosis (Cercospora beticola Saac).


Introduction
Beet (Beta vulgaris L.) is a plant species belonging to the Quenopodiacea family, originally from European and North African temperate regions, but today is grown in all continents. The edible part of the plant is a globular-shaped, usually a reddish-colored tuberous root rich in vitamins and minerals. This crop can be directly sown (seeds) or planted (seedlings) with bare root or germinated on trays with the substrate (Filgueira, 2012). For table beet production is usually necessary clay soils, with the large availability of mineral nutrients and high organic matter content (Sediyama et al., 2011;Xavier et al., 2013).
Vermiculite is a hydrated silicate mineral, containing varying amounts of iron, magnesium, potassium, and aluminum (Castro et al., 2011;Gooch, 2011), which can be used in adsorption of heavy metals due to its surface characteristics (Chui, 2005;França et al., 2006). The main applications of vermiculite in agriculture are as a substrate for plants (Curbelo, 2002), and as a seed germinator for many plant species (Vidigal et al., 2007;Araújo et al., 2020;Ferraz et al., 2020). In Brazil, the use of vermiculite in agriculture is still limited, and the suppliers are restricted to companies in the industrial and construction sectors (Ugarte et al., 2005).
Vermiculite is a viable alternative to support the in vitro propagation of sweet potatoes (Orellana, 2016), and its use has produced beet seedlings of higher quality than in coconut fiber (Oliveira, 2012). The main disadvantage is that vermiculite compresses easily, being able to collapse and lose its structure, an undesirable situation for long cycle crops but not for seedlings production (Villegas, 2017) or short-cycle crops.
Vermiculite is also non-phytotoxic, chemically, and texturally uniform in composition, with high water retention capacity, good aeration due to its physicochemical properties, ultra-lightweight, and is easily obtained (Figliolia et al., 1993;Vidigal et al., 2007). Due to those characteristics, vermiculite uses has been increasing . Thus, the objective of the work was to evaluate the effects of levels of vermiculite incorporated in the soil for beet production.

Methodology
The experiment was implemented at the São Paulo State University (UNESP), Botucatu campus, São Manuel, São Paulo state, Brazil, at 22°46' S and 48°34' W and 740 m above sea level. The prevailing climate is Cfa type (subtropical humid -Köppen's classification), with the average temperature of the hottest month superior to 22 °C, and 1,377 mm of average annual rainfall (Cunha and Martins, 2009). The experimental area and crop management were selected to represent an adequate crop condition for beet production.
The beet cultivar studied was "Early Wonder Tall Top". The beet seeds were sown in polypropylene trays (288 cells) containing commercial substrate and only one seed per cell. The initial soil fertilization included 20, 180 and 120 kg•ha -1 of N, P2O5 and K2O, respectively. The fertilization of the soil of the experimental area also included 90 kg•ha -1 of N as urea and 45 kg•ha -1 of potassium chloride (KCl) divided into three (3) applications, at 14, 28 and 42 days after transplanting (DAT) for all treatments. All fertilizations were done according to the recommendations of Raij et al. (1997) for beet production.
The soil preparation followed the recommendation by Filgueira (2012). The seedling transplanting to the field (October) happened 35 days after sowing (September). The soil beds where the beet seedlings were planted presented four (4) planting lines spaced by 0.25 m and the plants in line were spaced by 0.1 m.
The experimental design was also planned to represent an adequate condition to respond to questions about the viability of the use of vermiculite as a substrate component for beet production (Pereira et al., 2018); thus, the experiment was set as a randomized block design with 5 replications and the treatments were 0, 2, 4, 6, 8, and 10 t•ha -1 of vermiculite. The vermiculite was incorporated manually to reach a homogeneous distribution 15 days before the seedling transplant. The area of each experimental plot (soil bed) was 1x1 m 2 . Plants were irrigated with sprinklers and water was supplied up to maintain 60% of field capacity. Copper-based products were used to control cercosporiosis (C. beticola).
The beets harvest occurred at 52 DAT. Five randomly chosen plants were collected from the 2 central planting lines of each experimental plot. Plant height (mm), fresh and dry leaf weight (g plant -1 ) and diameter (mm), length (mm), fresh and dry weight (g plant -1 ) of roots were evaluated. The average yield was extrapolated to tones per hectare (t ha -1 ). All the results were subjected to the analysis of variance (F test) (p < 0.05) and the regression analyses (p < 0.05, R 2 > 0.70) using Sisvar 5.3 statistical software (Ferreira, 2011).

Results and Discussion
Plant height (32.41 cm) and the dry weight per plant of the leaf (5.81 g) and root (27.62 g) were not affected by vermiculite doses. For fresh leaf weight, a significant linear regression was detected, indicating the higher the vermiculite doses, the lower the fresh weights. This response can be observed in Figure 1 and indicates a reduction of 2.6571 grams of fresh leaf weight for each tone of vermiculite applied per hectare. Throughout this study, the high precipitation level (276.08 mm) and average daily maximum and minimum temperatures were 28.2 and 16.7 °C, respectively. The average air relative humidity was 75%. Vermiculite can improve soil water retention (Vidigal et al., 2007), and this favors the development of cercosporiosis (C. beticola) because a low incidence of this disease was observed where no vermiculite was added (t ha -1 ). Research, Society andDevelopment, v. 10, n. 1, e26810111157, 2021 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v10i1.11157 4 Cercosporiosis is also favored by high temperatures and prolonged periods of high air humidity and leaf wetting (Whitney and Duffus, 1986). A high number of leaf lesions, together with the accumulation of phytotoxins, induce leaf senescence, and the reduction in fresh weight (Weiland and Koch, 2004). Despite the incidence of C. beticola and the reductions in fresh weight with the addition of vermiculite, values were slightly higher than those reported by Silva et al. (2016) andMagro (2015), but lower than the indicated by Corrêa et al. (2014) and Candian et al. (2016).
The root length data adjusted to a quadratic model with a maximum length estimated at 2.62 t•ha -1 of vermiculite as it is presented in Figure 2. Although quadratic, the values obtained were similar to each other from the 0 to 4 t•ha -1 of vermiculite then decreased until 10 t•ha -1 . The beetroot diameter also adjusted to a quadratic model (Figure 3), with a diameter increase of up to 4.59 t•ha -1 of vermiculite and a pronounced decrease until 10 t•ha -1 . Due to the incidence of C. beticola, values were lower than those reported by Corrêa et al. (2014), Magro et al. (2015), Candian et al. (2016), and Silva et al. (2016). However, the root diameter of the beetroots can be classified as of good quality, according to Tivelli et al. (2011). Research, Society andDevelopment, v. 10, n. 1, e26810111157, 2021 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v10i1.11157  The values observed were lower than reported by Corrêa et al. (2014), Magro et al. (2015), Candian et al. (2016), and Silva et al. (2016), this was probably due to the excessive rainfall that favored the occurrence and establishment of cercosporiosis and use of an open-pollinated cultivar, while those authors studied hybrids that generally present superior productive potential.
For beet yield (t ha -1 ), the same tendency occurred where a significant reduction was observed due to the increasing levels of vermiculite ( Figure 5). Figure 5 indicates a reduction of 0.7479 ton ha -1 of beet production for each tone of vermiculite applied per hectare. Source: Authors.
The excess of soil moisture caused by rainfall, combined with vermiculite doses caused saturation of the system, increases the incidence of cercosporiosis. Plants attacked by C. beticola have decreased photosynthetic capacity and high use of reserves to repair leaf damage, increasing yield losses (Pittner et al., 2007). Beet plants are more sensitive to waterlogging in the third stage of growth (from complete hypocotyl formation to harvest) compared to the first and second stages of development (Costa et al., 2008).
Soil saturation also affects root respiration due to the decrease in soil airflow (Kerbauy, 2012). Coil aeration and porosity can be improved if vermiculite is associated with organic compounds (Caldeira et al., 2013). However, the use of vermiculite did not appear to provide an overall benefit to beet production.

Conclusions
The increase of vermiculite doses caused the linear decrease of the beet fresh root and leaf weight. Beet root length and diameter increased up to 2.62 and 4.59 t•ha -1 of vermiculite, respectively. The beet yield reductions observed were likely due to the high water holding capacity of vermiculite and to the consequent cercosporiosis incidence; The use of vermiculite solely in beet production did not seem to provide benefits for the cultivation of this crop. Future research should focus on lower ranges of vermiculite doses (< 2.62 t ha -1 ), and mixtures of vermiculite with other materials as a component for plant crop substrates, such as coconut husk fiber, crushed oyster shell, and sugar cane filter cake.