Initial production and quality of camu-camu fruits under organic and mineral fertilization

ABSTRACT Camu-camu [Myrciaria dubia (Kunth) McVaugh] is a native plant of the Amazon basin floodplains that is facing a domestication process in dry land. This study aimed to evaluate, qualitatively and quantitatively, camu-camu fruits obtained at the first harvest, in dry land areas, under mineral and organic fertilization. The experimental design was randomized blocks, with 10 treatments and 4 replications. Each experimental plot consisted of 4 lines with 5 holes (3 plants hole-1). Fertilization with organic residues (filter cake and compost + filter cake) every four months provided a higher fruit yield (326 g plant-1). However, the yield was lower when mineral fertilization or its combination with organic matter (76 ± 40 g plant-1) was used. Fertilization with filter cake + compost increased the fruit weight (8.91 g) and size (2.47 cm in diameter and 2.30 cm in length). The mineral and organic fertilization did not influence the chemical characteristics of the camu-camu fruits.


Camu-camu [Myrciaria dubia (Kunth) Mc
Vaugh] is a fruit tree that occurs in humid tropical climates, being naturally found in banks of rivers, lakes, floodplains and the flooded Amazon rainforest, in the following countries: Peru, Colombia, Venezuela and Brazil (Maeda et al. 2007, Hernández et al. 2011, Yuyama & Valente 2011. Its fruits contain high levels of ascorbic acid, which can be as high as 7,355 mg 1. Received: Oct. 18, 2019. Accepted: Mar. 04, 2020. Published: Apr. 27, 2020. DOI: 10.1590/1983 Camu-camu [Myrciaria dubia (Kunth) McVaugh] is a native plant of the Amazon basin floodplains that is facing a domestication process in dry land. This study aimed to evaluate, qualitatively and quantitatively, camu-camu fruits obtained at the first harvest, in dry land areas, under mineral and organic fertilization. The experimental design was randomized blocks, with 10 treatments and 4 replications. Each experimental plot consisted of 4 lines with 5 holes (3 plants hole -1 ). Fertilization with organic residues (filter cake and compost + filter cake) every four months provided a higher fruit yield (326 g plant -1 ). However, the yield was lower when mineral fertilization or its combination with organic matter (76 ± 40 g plant -1 ) was used. Fertilization with filter cake + compost increased the fruit weight (8.91 g) and size (2.47 cm in diameter and 2.30 cm in length). The mineral and organic fertilization did not influence the chemical characteristics of the camu-camu fruits.
e-ISSN 1983-4063 -www.agro.ufg.br/pat -Pesq. Agropec. Trop., Goiânia, v. 50, e60821, 2020 2011, Pinto et al. 2013). In addition, due to a difficult access to plants because of the flooding and short harvest period, the fruit is often harvested green, what impairs the ascorbic acid content, despite being climacteric (Pinto et al. 2013). In contrast, when cultivated on dry land, camu-camu can produce more than one crop per year and thus be harvested at its optimum ripeness, coinciding with the highest ascorbic acid content (Yuyama & Valente 2011).
Since camu-camu is naturally found both in low-acid soils and fertile floodplains of muddywater riverbanks and on less fertile acidic soils of black-water riverbanks, the fruit production and its respective contents, mainly ascorbic acid, may be variable (Hernández et al. 2011, Pinedo Panduro et al. 2011, Yuyama & Valente 2011. It is important to highlight that this adaptation to different environments allows a better agronomic management of the species (Welter et al. 2011, Yuyama & Valente 2011, Pinedo Panduro et al. 2018.
There is still no defined form of fertilization for the camu-camu production in non-flooded areas.
Research on the growth of camu-camu seedlings in an Oxisol A horizon as substrate indicates that the plant demands little, regarding nutrients, and seedling growth is often better without any fertilization (Yuyama & Valente 2011). On dry land, camu-camu has a satisfactory growth when fertilized with organic waste in the early years of planting, but the organic waste should be applied in small proportions or in parcels (Sousa 2009, Yuyama & Valente 2011. Abanto-Rodríguez et al. (2014) found that 160 kg ha -1 of potassium under a fertigation system provided better results, in relation to the height, diameter and number and total length of branches, as well as total mass and Dickson quality index, for the initial growth stage of camu-camu plants on dry land. In addition, Abanto-Rodríguez et al. (2018) evaluated the nutrients of camu-camu plants fertigated with nitrogen doses and found that doses greater than 128 kg ha -1 cause a decrease in biomass in the initial growth stage of plants.
Camu-camu is an important source of vitamin C (ascorbic acid), whose content in the fruit is influenced by various factors, such as fruit ripeness, soil nutrients, flood level in its environment and fertilization (Chagas et al 2015, Aguiar & Souza 2016, Grigio et al. 2016. In non-flooded environments, some researchers have found that camu-camu fertilization with N and K sources increased the ascorbic acid content in the fruits (Gavinho 2005, Abanto-Rodríguez et al. 2016.
In this context, this study aimed to evaluate fruit characteristics and ascorbic acid content of camu-camu under organic and mineral fertilization, by using sugarcane and guarana residues in the first years of planting, in a non-flooded area.

MATERIAL AND METHODS
The experiment was conducted during the months of January 2010 and January 2011, at the Usina Agropecuária Jayoro, in Presidente Figueiredo, Amazonas state, Brazil (01º96'04"S and 60º14'37"W), where the climate is Afi, according to the Köppen classification, with an average annual temperature of 26.7 ºC, average annual rainfall of around 2,419 mm and average relative humidity of 88 % (Carvalho & Molinari 2014).
The soil in the area is an Oxisol, according to the American classification (Latossolo by the Brazilian soil classification system; Embrapa 2018), which is poor in nutrients and has a high depth and high water permeability (USA 2014).
The orchard, consisting of accessions from Uatumã, Iquitos and Roraima, was propagated using seeds obtained from the camu-camu germplasm bank of the Instituto Nacional de Pesquisas da Amazônia (INPA). These were randomly selected from high yield and high ascorbic acid matrices.
The experimental design was randomized blocks, with 10 treatments and 4 replications. Each experimental plot consisted of 4 lines with 5 holes (3 plants hole -1 ). Thus, each treatment was e-ISSN 1983-4063 -www.agro.ufg.br/pat -Pesq. Agropec. Trop., Goiânia, v. 50, e60821, 2020 Initial production and quality of camu-camu fruits under organic and mineral fertilization composed of 60 plants with 5 m between rows and 2 m between holes. The treatments were: 1) no fertilization; 2) filter cake (2 L hole -1 ) every two months; 3) filter cake (2 L hole -1 ) every four months; 4) compost (2 L hole -1 ) every four months; 5) filter cake (2 L hole -1 ) + compost (2 L hole -1 ) every two months; 6) filter cake (2 L hole -1 ) + compost (2 L hole -1 ) every four months; 7) mineral (90-90-240 g/N-P 2 O 5 -K 2 O, corresponding to 200 g of urea, 500 g of triple superphosphate and 400 g of potassium chloride, divided into 3 applications) every four months; 8) mineral + filter cake (L hole -1 ) every four months; 9) mineral + compost (L hole -1 ) every four months; 10) mineral + filter cake + compost (L hole -1 ) every four months. Fertilization was performed manually at the base of the plant every year, for three years (April 2007 to December 2010). Leaf and soil samples were collected in April 2009 and May 2010, respectively. On these occasions, one soil sample was collected per plot, and was subsequently air-dried and sieved (2-mm mesh). The leaf analyses were performed by collecting leaf samples in the middle part of the canopy of five plants in each plot, and twenty leaves in total were collected from all the plots. These were dried in an oven at 65 ºC, for later analysis. The analysis of leaf and soil nutrient content followed the methods described and compiled by the Embrapa in 2009 and 2017, respectively.
For the yield analysis, fruits with more than 50 % of red area (ripeness) were collected every 14 days, from March 2010 to January 2011. The evaluated variables were: fruit yield (g plant -1 ); number of fruitbearing plants (%); average pulp weight plus skin (g); pulp yield plus skin (based on fruit and pulp; %); fruit weight (g), diameter and length (cm).
The data were subjected to analysis of variance by the F test and means compared by the Tukey test at 5 % of probability. A simple Pearson's correlation analysis at 5 % of probability was also used between fruit yield and soil and leaf chemical characteristics. The data for pulp yield and number of fruit-bearing plants were transformed to arc sine of √ x + 0.01, for the analysis of variance.

RESULTS AND DISCUSSION
The chemical analysis of the camu-camu leaves showed no nutritional deficiency according to the different fertilization treatments (Tables 1 and 2). Viégas et al. (2004), in similar tests, found similar levels of macro and micronutrients in camu-camu leaves, also an indicative of no deficiency symptoms. It can be observed that, for the micronutrient N, the majority of the treatments presented values greater than those found by Esashika et al. (2011) (18.2 g kg -1 ) and proportional to those observed by Abanto-Rodríguez et al. (2018) (22.8 g kg -1 ). On the other hand, the use of the compost every 4 months caused a lower N value in the leaves (13.7 g kg -1 ) ( Table 1).
The measurements of the camu-camu fruit yield revealed variations between the different (1) Mixture of sugarcane bagasse ash, filter cake and guarana seed husk in equal proportions; (2) N-P 2 O 5 -K 2 O. types of mineral and organic fertilization. The fruit yield, number of fruit-bearing plants, and pulp and skin weight were higher when the plants received fertilizers with compost + filter cake than when under mineral and organic fertilization. However, the peeled pulp yield did not vary, when comparing mineral and organic fertilization (Table 3). The highest fruit yield occurred in soils with 1.9 cmol c dm -3 and 1.0 cmol c dm -3 of exchangeable sum of base and 0.2 cmol c dm -3 and 1.0 cmol c dm -3 of Al content, which corresponded to filter cake fertilization every four months and filter cake + compost every four months, respectively (Table 4). Viégas et al. (2004) indicate that camucamu requires little Ca and Mg, what would partly explain the higher camu-camu fruit yield in low base saturation soils. On the other hand, the Al content found in the plots fertilized with compost + filter cake and filter cake every four months were similar to floodplains where camu-camu occurs naturally, justifying the higher fruit yield per plant in these treatments (Mafra et al. 2007, Fajardo et al. 2009, Yuyama & Valente 2011. Apparently, a rapid nutrient availability in the soil was detrimental to the camu-camu fruit production. The same behavior was also observed in camu-camu seedlings when there was a rapid change in the physical characteristics of the soil due to organic fertilization . Coincidentally, Sousa (2009), who studied camu-camu under the same conditions of this experiment, found that the camu-camu growth is more impaired by mineral fertilization than by organic fertilization in the first year of growing, and (1) Mixture of sugarcane bagasse ash, filter cake and guarana seed husk in equal proportions; (2) N-P 2 O 5 -K 2 O.
* Distinct lowercase letters in the columns for each variable differ from each other by the Tukey test at 5 % of probability; ns no significant difference.
(1) Mixture of sugarcane bagasse ash, filter cake and guarana seed husk in equal proportions; (2) N-P 2 O 5 -K 2 O. Initial production and quality of camu-camu fruits under organic and mineral fertilization this could have influenced the low fruit production in the experiment. The yield for peeled pulp ranged from 71 % to 77 % of the total fruit weight (Table 2), what corroborates the results found by Yuyama & Valente (2011) (73-86 %). The weight and size of the camucamu fruits showed a significant statistical difference under the distinct types of mineral and organic fertilization ( Table 5). The average fruit weight, diameter and height were higher under fertilization with compost + filter cake every four months than when the plants were under a combined fertilization with mineral and organic substances ( Table 5). The chemical parameters of the evaluated fruits showed no difference between the types of organic and mineral fertilization.
The pH and soluble solids (ºBrix) content did not present significant differences between the treatments with mineral and organic fertilizer, in this experiment. The average soluble solids content was 6.81 ºBrix, and the fruits had an average pH of 2.56 (Table 5). Other authors have also observed values ranging from 6.8 ºBrix to 9 ºBrix and pH ranging from 2.3 to 3.5 in camu-camu (Maeda et al. 2007, Yuyama & Valente 2011. The average ascorbic acid content did not show any significant difference, in relation to the treatments with mineral fertilizer and organic matter, with an average content of 1,993 mg 100 g -1 of pulp. On the other hand, there were plots with average contents of 2,554 mg and 4,043 mg of ascorbic acid per 100 g -1 of pulp under fertilization with filter cake + compost and mineral + filter cake + compost, respectively ( Figure 1).
The variation in the ascorbic acid levels within each plot is possibly due to the non-homogenization of the genetic material. On the other hand, this is the first report of a high content of ascorbic acid in orchards of camu-camu grown on upland areas. The study carried out found values of ascorbic acid ranging from 1,091 mg 100 g -1 to 3,465 mg 100 g -1 of pulp (Yuyama & Valente 2011). Since each plot was composed of 60 plants, an individual analysis of these could identify plants with even higher levels, which could be separated for later cloning.

CONCLUSIONS
Fertilization with compost (sugarcane bagasse ash, filter cake and guarana seed husk in equal proportions) + filter cake and only with filter cake, every four months, provide a higher fruit yield in camu-camu, while fertilization with filter cake + compost every four months increases the fruit average weight and size. Organic and mineral fertilization do not influence the pH or soluble solids of camucamu fruits. Ascorbic acid levels varied widely in the camu-camu samples analyzed, possibly due to the non-homogenization of the genetic material. Pulp and skin yield did not vary significantly under any type of fertilization, when compared to non-fertilized samples. fertilization: A) no fertilization; B) filter cake every two months; C) filter cake every four months; D) compost (mixture of sugarcane bagasse ash, filter cake and guarana seed husk in equal proportions) every four months; E) filter cake + compost every two months; F) filter cake + compost every four months; G) mineral (N-P 2 O 5 -K 2 O) every four months; H) mineral + filter cake every four months; I) mineral + compost every four months; J) mineral + filter cake + compost every four months.
A B C D E F G H I J 4,000.00 3,000.00 2,000.00 Ascorbic acid (mg 100 g -1 of fresh pulp)