ACCUMULATION AND EXPORT OF MICRONUTRIENTS IN POTATO FERTILIZED WITH ORGANIC-MINERAL FERTILIZER ACUMULAÇÃO E EXPORTAÇÃO DE MICRONUTRIENTES EM BATATA ADUBADA COM FERTILIZANTE ORGANO-MINERAL

: The response of potato plants to organo-mineral fertilization is still poorly understood. Hence, the aim of this study was to evaluate absorption and extraction of micronutrients by Agata potato cultivar in winter crop. The experiment was conducted in the municipality of Cristalina, Goiás state, Brazil, from May 26 to August 29 of 2012. The experimental design was a randomized block with five organo-mineral fertilizer rates, one mineral fertilizer rate (control) and four replications for each treatment. The results demonstrated that the mean total absorption of micronutrients by potato plants for the organo-mineral treatments was higher relative to the mineral treatment; and also that micronutrients were absorbed in the following order: Fe> Zn>Mn> Cu> B, in relation to total amounts. The average export of micronutrients in potato plants treated with organo-mineral fertilizer was 28%, 37%, 25%, 8% and 17% for Cu, Fe, Mn and Zn (respectively)relative to total amounts absorbed by the plants.


INTRODUCTION
Cultivation of potatoes, generally, involves high doses of fertilizers due to the fact that this crop is highly responsive to fertilization (CARDOSO et al., 2007).However, the major concern of potato growers is with the application of macronutrients (N, P, K), which can often result in hidden deficiency of micronutrients .In this case, the symptoms of deficiency are not visible; however, micronutrient-deficient crops deliver reduced tuber yield (RAIJ, 2001) of inferior quality (MESQUITA FILHO et al., 2001). Although micronutrients are absorbed at low concentrations, they have equal importance to macronutrients for crop growth (KRKBY; ROMHELD, 2007).
Micronutrient removal by potato plants and fertilization with highly pure mineral materials can lead to micronutrient deficiencies in potatoes after several years of cultivation (FILGUEIRA, 1993). Highly productive cultivars which usually demand high rates of macronutrients further exacerbate this problem . Still, according to Soratto et al. (2011), information regarding uptake and export of micronutrients in potato plants is scarce.
Absorption and extraction of micronutrients depends on external factors, such as cultivation environment, and also internal factors, such as genetic potential and plant age (BERTSCH, 2003).
For that reason, an accurate fertilization program for each cultivar, which optimizes the yield of tubers and prevents over-fertilization, predicates on studies of uptake and export of nutrients (ZOBIOLE et al., 2010).
Potato yields have nearly doubled in recent years in Brazil. They grew from 10 to 15 (t ha -1 ) in the 1980's to 25 to 30 (t ha -1 ) currently, and even above 40 (t ha -1 ) in some areas (FAOSTAT, 2016). The highest yields of tubers are obtained on the Brazilian cerrado soils. This fact gives cause for real concern about the need for correction and fertilization of these soils, which are characterized by high fixation of phosphorus (P), magnesium (Mg) and micronutrients (ARIMURA et al., 2007).
It is also known that the purpose of potato growing is to further increase the interaction between factors influencing growth, development and behavior of plants, such as: water, light, CO 2 , temperature, nutrients and genotype. Among them, fertilization is very important for most Brazilian soils which naturally present low fertility (FONTES;PEREIRA, 2003).
According to , the organomineral fertilizer is more efficient than exclusive fertilization with either organic or mineral materials. It is due to the fact that some of the fractions of the organic matter are humic substances, which enhance and stimulate microbial flora surrounding the root system, facilitate the release of nutrients, increase water retention, aeration, nutrient retention, aggregation, and mainly the formation of natural chelates, which directly influence plant nutrition (SOUZA; RESENDE, 2003).
Concerns about the use of organo-mineral fertilizers are high because their effect on the behavior of potato plants is still unknown. Therefore, the aim of this study was to evaluate absorption and removal of micronutrients by Agata potato cultivar in winter crop.

MATERIAL AND METHODS
The experiment was carried out in the municipality of Cristalina, Goiás state, Brazil on a site granted by the Agricultural Wehrmann® company. The experimental site is located at an altitude around 1189m, with an average rainfall 1426.3mm and average temperature 20.4°C. The planting of Agata potato cultivar was carried out on May 26, 2012 and harvested on August 29, 2012, being the winter crop.
The soil was classified as Oxisol with clayey texture (FERREIRA, 2010). The chemical analysis of soil samples extracted from depth of 0-20 cm (DONAGENA et al., 2011) showed the following results: pH 6.40 (CaCl 2 ), 3.6 g dm-3 soil organic matter and 50 mg dm -3 P (resin). The concentration of K, Ca and Mg in the soil was 161.00, 5.4 and 1.0 cmol c dm -3 , repectively, while H+Al stayed 2.00cmol c dm -3 . The micronutrients concentration of Zn, Cu, Fe, Mn and B was 12, 2.8, 33, 21,70 and 2.3 cmol c dm -3 , respectively. The base saturation was77%; andCEC was 8.80cmol c dm -3 . Thus, the experiment was conducted under conditions of high soil fertility according to the potato crop (MESQUITA et al., 2012).
The experimental design was a randomized block with six rates and four replications in the winter crop (Table 1). The experiment consisted of 24 plots, each with six rows10 m long spaced 0.8 m apart, totaling 48m² per plot. The evaluations were carried out on two central rows, disregarding two guard rows on each side of the block and a half meter at the ends of each row, totaling 14.4 m² of evaluation area per plot.
The organo-mineral fertilizer was based on poultry manure obtained from farms in the region. The production involved initially composting of the organic waste (poultry manure) by means of a controlled aerobic decomposition which lasted, on average, 20 days. To reduce the composting period and accelerate the decomposition process, nutrient cocktails and microorganisms (fungi and bacteria) were used yielding in a few days a stabilized compost. Next, the compost was amended with urea, triple superphosphate and potassium chloride to balance the nutrients, according to nutritional requirements for potato plants, soil fertility and soil nutritional status. Finally, the material was homogenized and pelletized.
The granules possessed a high degree of hardness (8 kgf cm -2 ), which creates high resistance to breakage and prevents formation of irregular particles. The organic material in the fertilizer: (i) provides physical protection, (ii) forms a porous matrix for the nutrients, and (iii) prevents direct contact of soluble nutrients with the soil. As a result, it promotes lower fixation and leaching losses (TEIXEIRA, 2013).
The chemical characterization of organomineral fertilizer was carried out in the laboratory is presented in Table 2.  (FILGUEIRA, 2008).
Fertilization was performed manually using hoes to incorporate the fertilizer into soil. Agata type 3 seed tubers (30-40 mm diameter) were planted in furrows.
Additional source of macro and micronutrients containing 2.7% Ca, 8.2% S, 12% Zn and 6 % B at a dose of 30 kg ha -1 was applied on all plots at planting, according to Souza & Lobato (2004)

recommendation for potatoes.
Hilling was performed about 30 days after planting in two seasons to stimulate tuberization. Hilling of the winter crop was additionally accompanied by topdressing with 300 (kg ha -1 ) of 20-00-20 formulation, justified by low rainfall during the period.
A central pivot irrigation system was used. The plants received approximately 500 mm of water during the cycle -a suitable volume for potato crops, which ranges between 450 and 550 mm (GRIMM et al., 2011).
At harvest, plant samples were done analysis of micronutrients Cu, Fe, Mn, Zn in leaves, stems and tubers. First, the sample material was washed. Then, the samples were placed in paper bags and taken to a stove with forced air circulation. After drying, the samples were ground in a mill with mesh number 20. The ground material was analyzed for nutrient content according to the methodology described by Embrapa (1999).
The accumulation of nutrients was calculated by multiplying the quantity of extracted nutrients and dry matter at each stage of plant development in each part of the plant. The nutrient export was obtained from the nutrient accumulation in the tubers at 89 DAP, that is, at harvest.
The data were submitted to analysis of variance to verify the existence of differences among the treatments. The comparison of the means for the treatments was carried out using the Scott Knott test at 0.05 significance. The datas for the treatments were submitted to polynomial regression analysis.

RESULTS AND DISCUSSION
Significant differences among treatments regarding the accumulation of all micronutrients (average) during the potato cycle (Table 3) were observed.
However, the accumulation of micronutrients in stems and leaves was higher for all organo-mineral treatments, except for copper (Cu) where treatment 1 (mineral fertilizer only) was statistically equal to treatment 3 (60%). Boron (B) levels in tubers in treatment 1 was higher than in treatments with organo-mineral fertilizer. Absorption of copper (Cu) and zinc (Zn) in tubers in treatment 1 was statistically equal to treatment 2 (40%) and treatment 3 (60%), respectively. Absorption of iron (Fe) in tubers was statistically equal in all treatments, except for treatment 6 (120%).
Similar behavior was also observed by Oliveira et al. (2007a), who found better agronomic effect of liquid organo-mineral fertilizers on vegetative growth of lettuce, cultivar Vera, relative to chemical fertilizer. Furthermore, studies carried out by Gonçalves et al. (2007) and Arimura et al. (2007), demonstrated higher yields of potatoes (Atlantic and Agata potatoes cultivars) under organo-mineral fertilizers, which was probably due to better uptake of nutrients.  found beneficial effect of organo-mineral fertilizer on tomato plants (Débora Pto cultivar), which expressed better production stability and better fruit quality in higher bunches, which according to the literature should occur there wise. According to , the positive effect of the organo-mineral fertilizer is directly linked to organic compounds in its composition which generally optimize the uptake of nutrients.
Studies conducted by Bruno et al. (2007) and Oliveira et al. (2007b) concluded that organo-mineral fertilizers improve crop productivity and plant morphological parameters such as length and diameter of roots, and improve the uptake of nutrients by roots (PEDROSA et al., 2007). Kaseker et al. (2014) evaluating the effects of organomineral fertilizers on carrot, also noted increased accumulation of nutrients in plants, even in a highly fertile soil -conditions similar to this studyemphasizing, therefore, better efficiency of organomineral fertilizers.   Figure 2 shows total absorption curves (sum of stems, leaves and tubercle), during the potato crop cycle.
Maximum accumulation of B in stems was 30,49 (g ha -1 ) at 74 days after planting (DAP) ( Figure 1A). These results are considerably higher than 8.50 and 10.10(g ha -1 ), respectively, found by Soratto et al. (2011) for 'Asterix' and 'Mondial' cultivars, which had been the largest accumulation values found by researches working with five potato cultivars treated with mineral fertilizer. Regarding Agata cultivar, Fernandez (2010) found maximum accumulation in stems 4.80 (g ha -1 ) at 71 DAP, working in the municipality of Itaí, São Paulo state.
The maximum Cu accumulation in stems was 17.80(g ha -1 ) at 61 DAP ( Figure 1B). Again, this result is different from 1.73 (g ha -1 ) found by Fernandez (2010) for Agata cultivar at 77 DAP. The same author found 5.63 (g ha -1 ) of accumulated Cu in Mondial potato cultivar. The maximum Fe accumulation in stems was 664.10(g ha -1 ) ( Figure 1C) at 61 DAP; higher than 131.37 (g ha -1 ) presented by Soratto et al. (2011) for Agata cultivar. The maximum levels of Mn and Zn accumulated in stems were 35.50 and 116.57 (g ha -1 ) 61 DAP, respectively ( Figures 1D  and 1E), which are different from 39.80(g ha -1 ) of Mn and 18.00(g ha -1 ) of Zn observed by  also for Agata potato cultivar.
Except for Mn, micronutrient levels in potato tubers grew until the end of the cycle. However B, Cu and Fe accumulation intensified 60 DAP, which can be seen in the accumulation curve ( Figures 1A, 1B, 1C). Cabalceta et al. (2005), postulated that B content in tubers from the beginning of their formation is due to the fact that B participates in growth and cell division of meristematic tissues, formation of cell walls, and starch translocation from tops to tubers. Thus, as the development of tubers is preceded by intense process of division and cell elongation in the subapical region of stolons, rapid accumulation of B in tubers under formation is common (CABALCETA et al., 2005).  (FERNANDEZ et al., 2011). Cabalceta et al. (2005) found that nutrients absorbed by potatoes in the early stages of the cycle are mainly accumulated in the shoots; however, in the final phase of the cycle most of shoot nutrients are translocated to tubers. Moreover, according to Fernandez et al. (2010), falling leaves and translocation to tubers decrease the amount of nutrients.
The maximum accumulation of micronutrients during the production cycle of Agata potato cultivar was 77.00(g ha -1 ) B; 90.82 (g ha -1 ) Cu; 3808.08 (g ha -1 ) Fe; 195.90 (g ha -1 ) Mn and 204.50(g ha -1 ) Zn. The accumulation of nutrients varies according to productivity, season, environmental conditions, and plant development phase; which occur during vegetative growth and intensify during flowering and formation of fruits and tubers (CARDOSO, 2014).
The accumulation of nutrients in tubers at the end of the cycle corresponds to the total accumulation during the cycle. There was a statistically significant difference among treatments with organo-mineral and mineral fertilizers. However, no significant differences among total yield of tubers per hectare were observed (Table 4). As demonstrated in the discussion above, the export of micronutrients, either per hectare or per ton of tubers, vary widely in the literature. It is also important to point out that the comparisons had to be carried out using results obtained in studies with conventional fertilization, i.e. mineral fertilizers. This fact reinforces the importance of intensifying studies with organo-mineral fertilizers to gain better understanding of their behavior in soil-plant system. Thus, more research work under different soil conditions, climate and management systems must be carried out to better recognize the benefits of organo-mineral fertilizers and also their constraints.

CONCLUSIONS
The mean total absorption of micronutrients by potato plants for the organo-mineral treatments was higher than for the mineral treatment.
The average export of micronutrients for the organo-mineral treatments relative to total amounts of micronutrients absorbed by potato plants were: 28%, 37%, 25%, 8% and 17% for Cu, Fe, Mn and Zn, respectively.