Uptake and Exportation of Micronutrients by Transgenic Cultivars of Maize Under No-tillage in the Brazilian Cerrado

Introducing cultivars of high productive potential with adequate agronomic management has contributed to the increase of maize yield in Brazil. This study aimed to characterize the extraction and exportation of micronutrients by modern maize hybrids grown in no-tillage system in the Cerrado region (Brazilian Savannah) with two fertilization levels. We established two crop environments with differentiated levels of soil fertilization, use of products for seed treatment and leaf fertilization, in which four transgenic hybrids were grown. For each environment, we used an experimental design of randomized blocks with four replicates. There were eleven plant samplings during the crop cycle to quantify dry mass production and Cu, Fe, Mn and Zn extraction. Micronutrient uptake is increased when a hybrid with higher potential for biomass production grows in an environment with greater supply of nutrients. Uptake persists throughout the maize cycle, including during the final stages of the reproductive phase, showing late demand for the crop. On average, after tasseling, about 39, 50, 42, and 49% of the total Cu, Fe, Mn and Zn absorption still occurs, respectively. Total uptake of Cu, Fe, Mn and Zn are, respectively, around 8, 199, 58 and 40 g to produce a tonne of grain, from which 23, 5, 8, and 42% are exported by the harvest. Micronutrient uptake and exportation rates for the studied transgenic hybrids are lower than the ones previously reported in Brazil and in works abroad.

In 2012, the area was divided into two environments, under medium or high technological investment in fertilization (Padilha et al., 2015). In November 2014, before assembling the experiment for the study, 2 t ha -1 dolomitic limestone, 1 t ha -1 gypsum and 200 kg ha -1 mixture of 3:1 potassium chloride and FTE BR 12 were spread in the environment with high investment, in order to provide soil fertility differential conditions.
On December 17, 2014, four transgenic maize hybrids were sown (AG 8088 PRO X, DKB 310 PRO 2, DKB 390 PRO and P 30F53 YH) in high and medium fertilization environments using plot spacing seeder of 0.5 m between rows and 70,000 seeds per hectare. The cultivation occurred with complementary irrigation managed under no-tillage system.
In each environment, the experimental design took place in randomized blocks with four replicates. Plots consisted of four 6 m rows in length; the two central rows with one-meter border at the ends were the useful area (4 m 2 ). There were duplicated plots of each treatment in order to collect plants along the cycle to determine the micronutrient absorption march, and to evaluate the grain yield after physiological maturation.
At 20 DAS, soil sampling took place to characterize the fertility conditions for maize cultivation, at a 0-20 cm depth (Table 1), following analytical methodologies using the Mehlich 1 extractant for Cu, Fe, Mn and Zn, and hot water for B, as described by Silva (2009). Herbicides and insecticides were used in phytosanitary treatments, according to technical criteria for the control of weeds and caterpillars.  H+Al  CTC  V 2  m 3   Water  dag kg -1  -----mg dm -3 ----------------------cmol c dm -3 ----------------------% --- We harvested the useful area from the plots to perform grain yield evaluation after physiological maturation. Productivity corrected to 13% humidity was used to calculate the micronutrient accumulation in the grains at the end of the maize cycle, corresponding to the quantities exported with the harvest.
For each phenological stage, the variables were submitted to joint analysis of variance, in order to verify the existence of interaction between hybrids and fertilization investment environments. Grouping test of Scott-Knott averages 5% probability compared treatments for dry mass production and micronutrient accumulation in different phenological stages as well as grain yield, with the aid of statistical program SISVAR (Ferreira, 2011).

Results and Discussion
For the total dry mass at physiological maturation (stage R6), there was a significant effect of investment environments on fertilization and hybrids. On average, the dry mass accumulation up to this stage was approximately 25,627 kg ha -1 (Table 2) with an order partition of 10, 28, 16 and 43% between the leaf, stem, straw + cob and grain compartments, respectively ( Figure 1). Dry mass production was statistically different between the high and medium investment environments (Table 2), with a difference of 10.8%, showing a considerable response due to the improvement of soil fertility by higher fertilization, which should have an impact also in the quantities of micronutrients. In both environments, accumulation of dry mass until flowering (stage R1, 64 DAS) reached a little less than half (45.9%) of the total (Figure 1), becoming more intense later, so that in the 40 following days (stage R5, 104 DAS), the crop reached 95% of total dry mass production.
jas.ccsenet.   extraction capacity compared to the others, totaling 107.5 g ha -1 , a difference of 43% in relation to the lowest average (AG 8088), which is in agreement with its high potential for dry mass and grain production ( Table 2).
The highest Cu extraction from the environment with high investment (Table 3) is probably due to the higher fertilization level that has been adopted over time, which intensifies maize development. Thus, greater accumulation of dry mass is expected to have direct reflection in the extraction of nutrients available in that environment.
Maximum extraction of this micronutrient was only completed in the physiological maturation, corresponding to 98 and 73 g ha -1 in the high and medium fertilization environments, respectively (Table 3 and Figure 2). On average, up to 61.5% of the maximum accumulation was observed up to the bolting stage (VT), showing that a considerable part of Cu absorption occurs later, after crop anthesis. Note. For each variable, averages followed by the same letter in the row do not differ by Scott-Knott test at 5% probability.
These results are in agreement with Bender (2013), which reported that in the period before flowering only half of the total Cu accumulation has occurred. Maximum Cu extraction point determined by Andrade et al. (1975b) was between 101 and 108 days after emergence, and Borges et al. (2009) Figure 3. Iron uptake during maize cycle grown in environments with high (a) and medium (b) investment in fertilization. Average of four hybrids Total Fe uptake data were close to 1,900 g ha -1 , value reported by Karlen et al. (1988), higher than the average of 1,100 g ha -1 found by Bender et al. (2013) in a study with transgenic hybrids in the USA. However, this value is below the 3,296 g ha -1 reported by Duarte et al. (2003) as the average of cultivars from temperate and tropical climate evaluated in Brazil. The patterns of Fe extraction by maize may be quite variable, according to environments, soil conditions, hybrids and other handling practices established in the crop.
The trend of Fe accumulation in physiological maturation in different parts of the plant was similar in both environments, with 48, 42, 5, and 5% distributed in leaf, stem, cob + straw and grains, respectively ( Figure 3). Thus, leaves and stem are the main sites of Fe deposition absorbed by maize, while the grains do not represent a strong drain of this micronutrient. The surface liming (2 t ha -1 ), performed before the start of the experiment in the high investment environment, did not affect Fe acquisition by maize. This is consistent with the absence of significant alterations in pH data in soil analysis, although the available levels of Fe (Table 1) are interpreted as low and medium (Alvarez et al., 1999), in high and medium investment, respectively.
On average, for each tonne of grain, maize extracted 199 g Fe, close to Ciampitti & Vyn (2013), which quantified absorption of 194 g t -1 . In spite of being the micronutrient extracted in greater quantity by maize plants (Table 3), Fe proportion allocated in the grains was relatively low, about 5.4% of the total extracted. This proportion corresponds to an exportation of 10.6 g t -1 , a rate lower than reported by Bender et al. (2013) and Ciampitti and Vyn (2013), of 20.7 and 32.3 g t -1 , respectively.
In the case of manganese (Mn), the extraction was influenced by the hybrids and fertilization environments in several stages from V5, including the evaluation performed in the physiological maturation (R6). However, there was no interaction between these factors. Among the hybrids, DKB 310 stood out in Mn accumulation, with significantly higher content than the other hybrids, especially at the end of the cycle, in the R5 and R6 stages. Similar to Cu and Fe extraction, when expressing the highest potential of dry mass and grain yield, DKB 310 hybrid also exhibited higher Mn requirement.
High investment environment in fertilization promoted greater Mn accumulation starting in V5; the total extraction in the physiological maturation was 778 and 500 g ha -1 in the environments of high and medium investment, respectively (Table 3). These quantities are below the 900 g ha -1 quantified by Karlen et al. (1988); however, close to the values obtained by Duarte et al. (2003) and Andrade et al. (1975b), of 638 g ha -1 and 496 to 720 g ha -1 , respectively.
After Fe, Mn was the second micronutrient with the highest extraction by maize plants. The most expressive accumulation under high technological investment (Table 3, Figure 4) may be associated with the greater potential of dry mass production by hybrids (Table 2)

Conclusions
Micronutrient uptake is increased when a hybrid with higher potential for biomass production grows in an environment with greater supply of nutrients.
Micronutrient uptake persists throughout the maize cycle, including during the final stages of the reproductive phase, showing late demand for the crop. On average, after tasseling, about 39, 50, 42, and 49% of the total Cu, Fe, Mn and Zn absorption still occurs, respectively.
Total uptake of Cu, Fe, Mn and Zn are, respectively, around 8, 199, 58 and 40 g to produce a tonne of grain, from which 23, 5, 8, and 42% are exported by the harvest.
Micronutrient uptake and exportation rates for the studied transgenic hybrids are lower than the ones previously reported in Brazil and in works abroad.