Use of cassava wastewater in Capsicum chinense production

ABSTRACT The use of resources derived from the agricultural property itself to meet the needs of producers promotes the reduction of costs with commercial inputs and recycling of by-products, among them the liquid waste from the cassava flour production, called cassava wastewater, which can be an important fertilization source. This study aimed to evaluate the growth and production of Capsicum chinense Jacq., as a function of cassava wastewater doses associated with mineral fertilizer proportions. The experiment was conducted in a greenhouse, in a completely randomized design, with treatments distributed in a 3 x 5 factorial scheme, corresponding to 3 doses (0, 50 and 100 %) of the mineral fertilization recommended for the crop and 5 doses (0, 25, 50, 100 and 150 m³ ha-1) of cassava wastewater, with 4 replicates. The cassava wastewater doses influenced the crop yield, showing a linear trend. The dose of 150 m3 ha-1 promoted a yield equivalent to that obtained with the application of 100 % of the mineral fertilization recommended for this crop, thus enabling the partial or total replacement of this fertilization by cassava wastewater.

The use of resources derived from the agricultural property itself to meet the needs of producers promotes the reduction of costs with commercial inputs and recycling of by-products, among them the liquid waste from the cassava flour production, called cassava wastewater, which can be an important fertilization source. This study aimed to evaluate the growth and production of Capsicum chinense Jacq., as a function of cassava wastewater doses associated with mineral fertilizer proportions. The experiment was conducted in a greenhouse, in a completely randomized design, with treatments distributed in a 3 x 5 factorial scheme, corresponding to 3 doses (0, 50 and 100 %) of the mineral fertilization recommended for the crop and 5 doses (0, 25, 50, 100 and 150 m³ ha -1 ) of cassava wastewater, with 4 replicates. The cassava wastewater doses influenced the crop yield, showing a linear trend. The dose of 150 m 3 ha -1 promoted a yield equivalent to that obtained with the application of 100 % of the mineral fertilization recommended for this crop, thus enabling the partial or total replacement of this fertilization by cassava wastewater.

PALAVRAS
Concerning the 2006 agricultural census, the highest pepper yields were obtained in properties fertilized with mineral fertilizers (7,238 t) and with the joint use of mineral and organic fertilizers (7,108 t), followed by only organic fertilizers (2,977 t) and agricultural units that did not use fertilization (1,360 t) (IBGE 2006). Costa et al. (2019) highlighted the importance of using resources derived from the agricultural property itself to meet the needs of producers, promoting the recycling of by-products and reduction of costs with commercial inputs. In this context, the liquid waste from the cassava flour production may be an important source of organic fertilization.
Cassava wastewater is released during the cassava flour production and is characterized by a high organic load, fibers, starch, cyanogenic compounds and nutrients such as nitrogen, phosphorus, potassium, calcium and magnesium (Araújo et al. 2015, Bezerra et al. 2017, Sánchez et al. 2017. In northeastern Brazil, most cassava wastewater is produced in small facilities and discharged directly into the soil, causing aesthetic and environmental inconveniences in the vicinity of flour mills (Araujo & Lopes 2009, Sánchez et al. 2017. Among the problems caused by the indiscriminate discharge of the effluent, it is possible to highlight the contamination of surface and underground water and alteration in the soil physical and chemical attributes, in addition to the formation of huge lakes and release of unpleasant odors, attracting rodents and insects (Araujo & Lopes 2009).
These problems are mainly associated with the large volume of effluents released into the environment. Ponte (2006) describes that, for every 3 kg of pressed cassava roots, about 1 L of cassava wastewater is generated. Based on this mean proportion, if the 963,000 t of cassava roots produced in Bahia, in 2019 (IBGE 2019), were processed for flour production, about 321,000 m 3 of cassava wastewater would be released.
Studies have been conducted to make use of this effluent efficiently. Vieites (1998), when studying the effects of cassava wastewater replacing mineral fertilization in tomato cultivation, observed that this effluent contributed to increasing the yield, diameter and length of tomato fruits. When using cassava wastewater in bell pepper fertilization, Lima & Valente (2017) noticed that it promoted significant effects on fruit length and diameter. Araújo et al. (2015), when analyzing the growth and yield of maize fertilized with cassava wastewater doses, reported that this effluent was effective for plant growth. Bezerra et al. (2017) used cassava wastewater as a source of organic fertilizer in 'Marandu' palisade grass pasture and observed that the increase of effluent depths promoted a greater forage biomass and reduction of spontaneous plants.
Thus, the use of cassava wastewater as a fertilizer is an opportunity to simultaneously reduce the problems caused by its indiscriminate disposal around the flour mills, improving the environmental quality and promoting an increase in crop yield and savings with mineral fertilizers.
Therefore, considering its significant organic load and the presence of essential nutrients for plant development, the hypothesis of this study is that cassava wastewater may be used as an organic fertilizer in the cultivation of C. chinense, partially or totally replacing the mineral fertilization. Thus, the present study aimed to evaluate the growth and yield of C. chinense, as a function of cassava wastewater doses associated with mineral fertilizer proportions.

MATERIAL AND METHODS
The study was conducted in a greenhouse of the Universidade Federal do Recôncavo da Bahia, in Cruz das Almas, Bahia state, Brazil (12º39'48.84"S, 39º5'15.17"W and altitude of 220 m), from May to October 2019. According to the Köppen-Geiger classification, the region has a humid tropical climate (Af), with occurrence of precipitation in almost all months of the year (Alvares et al. 2014).
A randomized block design was used, with treatments distributed in a 3 x 5 factorial scheme, with four replicates, totaling 60 experimental units, with spacing of 0.50 m between experimental units and 0.80 m between blocks. The treatments were randomly distributed in each block. The blocks remained fixed in the same place in the greenhouse throughout the cycle.
The cassava wastewater was obtained from a cassava processing mill located in Cruz das Almas, in the Sapucaia community, about 3 km from the experimental area. The samples were collected directly from the press, transferred to a container with capacity for 50 L and transported to the experimental area. It is worth mentioning that the container with cassava wastewater was left open and at rest for seven days, at room temperature, for hydrocyanic acid volatilization. A sample of the effluent after the treatment was kept in a refrigerated environment for analysis aimed at its characterization (Table 1).
Capsicum chinense, marketed by ISLA Sementes, was sown in a tray containing coconut fiber and cattle manure at a 3:1 ratio, respectively. Transplanting was performed at 60 days after sowing, when the seedlings had 4-5 developed leaves, planting one plant per pot.
Mercury tensiometers were used for irrigation management, with soil water tension daily readings during the early hours of the morning. Irrigation was carried out with public-supply water, using a graduated cylinder, restoring the moisture to the level equivalent to a 10 kPa tension, in order to meet the water needs of the crop. Manual weeding was performed whenever necessary to keep the crop free of spontaneous plants.
The following growth components were analyzed at 100 days after transplanting (DAT): plant height, stem diameter, number of leaves, leaf area, shoot dry mass and chlorophyll index (total, a and b). In relation to the production, the number of fruits, yield, fruit fresh mass, length and diameter, fruit tip length and fruit wall thickness were determined. For this, 10 fruits were randomly selected in each treatment, using the mean of the measured values.
The plant height was determined with a millimeter tape, from the plant collar to the apical bud. The number of leaves and number of fruits were obtained by direct counting. The stem diameter and the variables fruit length, fruit diameter, fruit tip length and fruit wall thickness were measured with a digital caliper (accuracy of 0.01 mm). The tip length was determined from the point at which the fruit diameter was 0.005 m up to the thinnest end.
The total yield was obtained by multiplying the fresh fruit mass by the number of plants in (1)  1 hectare, considering the recommended spacing, in a total of 25,000 plants per hectare. The leaf area was determined by the disc method (Camargo 1992). Chlorophyll was measured by indirect readings of leaf chlorophyll, using the portable chlorophyll meter Falker ClorofiLOG™ 1030 (Schlichting et al. 2015). The shoot dry mass, fruit dry mass and fruit fresh mass were determined using a precision scale. The dry masses were obtained after drying in a forced ventilation oven at 65 ºC, until reaching a constant weight.
The results obtained for all variables were subjected to analysis of variance and F test. The means of qualitative variables were subjected to the Tukey test (p ≤ 0.05) and the means of quantitative variables to regression analysis. The models were chosen according to their significance by the F test (p ≤ 0.05) and coefficient of determination (R²), using the Sisvar software, version 5.6 (Ferreira 2019).

RESULTS AND DISCUSSION
The applied treatments caused significant differences for plant height (p ≤ 0.05 for mineral fertilization and p ≤ 0.01 for cassava wastewater), stem diameter, number of leaves, leaf area, total chlorophyll content, chlorophyll a content and shoot dry mass (p ≤ 0.01) of C. chinense at 100 days after transplanting (DAT) ( Table 2). Likewise, there was significance for the interaction between mineral fertilization and cassava wastewater doses (p ≤ 0.05 or p ≤ 0.01), except for stem diameter and shoot dry mass.
The treatments that received the mineral fertilizer dose recommended for pepper crop were the most responsive ones, regarding the variables stem diameter ( Figure 1A) and shoot dry mass ( Figure 1C), at 100 DAT. In relation to the cassava wastewater doses, these variables showed a tendency to increase linearly ( Figures 1B and 1D). This is probably related to the composition of the cassava wastewater, due to the abundance of nutrients, especially potassium, an element that has important functions in plant cells and tissues (Kerbauy 2004). In the present study, the cassava wastewater contained essential nutrients for the plant development, especially high concentrations of K and P ( Table 1).
The decomposition of the significant interaction between mineral fertilization and cassava wastewater for plant height, number of leaves, leaf area, total chlorophyll, chlorophyll a and chlorophyll b of C. chinense demonstrated that the treatments were influenced by the maximum dose of cassava wastewater applied with different mineral fertilization proportions (Figure 2).
The plant height increased linearly with the increment in the cassava wastewater doses for the different proportions of mineral fertilization (Figure 2A). Similarly, the number of leaves ( Figure 2B) and leaf area ( Figure 2C) showed a linear trend with the increment in the cassava wastewater doses. These results demonstrate that the nutrients present in the cassava wastewater (Table 1) promoted beneficial effects for the C. chinense; so, it is necessary to carry out studies with higher doses to evaluate the maximum potential of the crop.
The variables total chlorophyll ( Figure 2D), chlorophyll a ( Figure 2E) and chlorophyll b ( Figure  2F) showed a negative linear trend as the cassava wastewater doses increased, with significance only for CV: coefficient of variation; SV: source of variation; DF: degree of freedom; FCI: Falker chlorophyll index; ns not significant; * significant at p ≤ 0.05; ** significant at p ≤ 0.01. Use of cassava wastewater in Capsicum chinense production the treatments with absence of mineral fertilization. Nitrogen deficiency induces a lower chlorophyll content, because it is a constituent of the molecule. Pagliarini et al. (2014) described that the reduction in the chlorophyll content of C. chinense may be associated with nitrogen leaching along the cycle. In addition, there may be nitrogen immobilization by microorganisms. Regarding the variables yield and fruit wall thickness, the analysis of variance showed a significant effect (p ≤ 0.01) for the factors mineral fertilization and cassava wastewater, individually, with no significant effect for the interactions between them (Table 3).

SV
It was possible to observe that the different proportions of mineral fertilizer alone influenced the crop yield, with a 52 % increase under 50 % of the recommended fertilization and 120 % increase under the full dose, if compared to the treatments that did not receive fertilization ( Figure 3A). The cassava wastewater doses influenced the crop yield, which showed a linear trend ( Figure 3B). According to Vieites (1998), the increase in yield is related to the chemical composition of the cassava wastewater, as it contains approximately 92.98 % of water, facilitating the direct absorption of nutrients such as potassium, nitrogen, phosphorus and calcium. Cassava wastewater doses (m 3 ha -1 ) Mineral fertilizer proportions CV: coefficient of variation; SV: source of variation; DF: degree of freedom; ns not significant; * significant at p ≤ 0.05; ** significant at p ≤ 0.01.   For fruit wall thickness, there was no difference between the treatments with 0 and 50 % of mineral fertilization, and the dose of 100 % stood out ( Figure 3C). On the other hand, the cassava wastewater promoted a linear increase, with thickness of 2.7 mm in the treatments that received 150 m³ ha -1 of cassava wastewater ( Figure 3D). Abud et al. (2018) reported that the fruit wall thickness is an important characteristic, especially when it comes to fruits consumed fresh, because fruits with thicker walls are more resistant to postharvest treatments. Jorge et al. (2018) recorded values for peel thickness, according to the maturity stage of C. chinense, and found values of 1.30 mm for green fruits, 1.80 mm for orangecolored fruits and 2.04 mm for red fruits, that is, fully ripe. According to these authors, ripe fruits are more turgid due to their higher water content. Therefore, the fruits may have a larger diameter and higher fresh mass, as observed in the present study.

SV
By analyzing the decomposition of the interaction for number of fruits ( Figure 4A), it was possible to observe a linear increase with the increase in the cassava wastewater doses, as a function of the fertilizer proportions, with a certain parallelism among the three regressions, with lower values for the dose of 0 % and higher values for 100 %. For the bell pepper crop, there was a linear reduction in the number of fruits with the increase in the cassava wastewater doses (0, 20, 40, 60 and 80 mL) applied weekly in the holes (Lima & Valente 2017).
The variable fruit length ( Figure 4B) showed a quadratic trend for the treatments with absence of mineral fertilizer, with an ideal dose estimated at 102 m³ ha -1 of cassava wastewater, and linear trend for treatments with 100 % of the fertilization recommended for the crop, promoting an increase of approximately 0.018 mm for each increment in the dose.  Regarding the fruit diameter ( Figure 4C), there was a quadratic trend for the applied doses, as a function of the fertilizer proportions. According to the derivative of the regression equation, the ideal dose for application of only cassava wastewater was equivalent to 91 m³ ha -1 , for a maximum fruit diameter of 18.0 mm. For 100 % mineral fertilization, the ideal dose estimated was 86 m³ ha -1 , for a maximum fruit diameter of 16.2 mm. For the bell pepper crop, Lima & Valente (2017) observed a quadratic trend in fruit diameter, as a function of the increase in the cassava wastewater doses (0, 20, 40, 60 and 80 mL), with an ideal dose of 16 mL. Vieites (1998) describes that the increase in fruit diameter and length with the increase in the cassava wastewater doses is probably related to their potassium content, due to its role in the translocation of carbohydrates, and also to the large amount of calcium, which contributes to preserving the integrity and functionality of cell membranes and maintaining a firm tissue consistency.
The fruit tip length ( Figure 4D) showed significance only for the absence of mineral fertilization, with a quadratic trend and an ideal dose equivalent to 87 m³ ha -1 of cassava wastewater, with an estimated length of 8.4 mm. A study conducted by Heinrich et al. (2015) recorded a variation of 1.5-6.3 mm in the fruit tip length in self-fertilized salmon-colored C. chinense.
The variable fruit fresh mass ( Figure 4E) was influenced by the cassava wastewater doses and mineral fertilization proportions. A linear trend was observed for the treatments subjected to 100 % of mineral fertilization, with a mean increase of 0.18 g with the increase in the doses, and a quadratic trend was observed for 0 and 50 % of mineral fertilization, with an ideal dose of 100 m³ ha -1 of cassava wastewater, which led to a fruit fresh mass of 2.47 and 2.39 g, respectively. Abud et al. (2018) observed a fruit fresh mass of 1.29 g for C. chinense, and this value decreased as the fruits ripened. Bione (2017) obtained a fruit fresh mass equivalent to 1.6 g per ripe fruit, in the hydroponic cultivation of C. chinense, for the control treatment (composed of public-supply water and nutrient solution). Thus, it was observed that plants under mineral fertilizer doses of 50 and 100 % with the addition of 100 m -3 ha -1 of cassava wastewater produced peppers with superior fresh mass per fruit, even under ideal hydroponic system conditions.
The fruit dry mass ( Figure 4F) showed a linear trend for full fertilization (100 %) and a quadratic trend for 0 and 50 % of mineral fertilization. According to the derivative of the regression equation, for 50 % of mineral fertilization the ideal dose of cassava wastewater was equivalent to 105 m³ ha -1 , promoting a dry mass of 0.34 g, and to 98 m³ ha -1 for treatments in the absence of mineral fertilization, with an estimated dry mass of 0.36 g per fruit. Abud et al. (2018) evaluated C. chinense fruits at different maturity stages and found a mean value of 0.18 g per fruit. These authors reported that there is loss of water during the fruit maturation through transpiration, especially at the end of this process, favoring the reduction in the weight of ripe fruits.

CONCLUSION
The single application of cassava wastewater, at a dose of 150 m 3 ha -1 , promotes an yield of Capsicum chinense equivalent to that obtained with the application of 100 % of the mineral fertilization recommended for this crop, thus enabling the partial or total replacement of this fertilization with cassava wastewater.