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Productivity and yield components of corn fertilized with different sources and levels of zinc.

Short title: Corn fertilization with different sources and levels of zinc

1. Introduction

The search for higher productivities in crops of Brazil is a constant and current challenge, however, this increase in income must be coupled with scientific and technological advancement, being necessary studies with regard to knowledge of nutritional requirements for each crop, thus improving themselves the use of fertilizers on the farm (Goncalves Jr. et al., 2010).

Corn crop (Zea mays L.) is the most important cereal grown in Brazil, which is in 3rd place in the worldwide rank production of this crop (behind the United States and China), cultivating 12.86 million ha and harvesting 55.61 million tons of grains in its two annual harvests. The State of Parana is the largest corn producer in Brazil, cultivating a 2.27 million ha area and producing 13.54 million tons, where, the farmers use a medium technology level (Instituto Brasileiro de Geografia e Estatistica, 2010).

Among the micronutrients used in agriculture, the supply of zinc (Zn) reflects the higher responses for the corn culture in Brazilian soils, either by its low contents in the soil, associated or not with the liming practice, phosphorus fertilizing, or organic matter contents of soil (Coutinho et al., 2001).

According to Furlani et al. (2005), acid soils of low fertility and high fertility soils with excess of lime, often have deficiencies of micronutrients in annual and perennial crops, especially the Zn deficiency in corn culture.

The knowledge of the need for Zn in corn crop resulted in the production and marketing of macronutrients fertilizers supplemented with micronutrients, in this case the Zn, with a higher price than other fertilizers and the promise of improved productivity in all Brazil. But, the field results show that is not always necessary the use of micronutrient Zn, once the various soils types of Brazil have different fertility levels. Should also highlight, the importance of evaluate the products marketed in Brazil, assessing, in this case, if the raw materials used to manufacture fertilizers have good quality.

This way, seeking assess different sources and levels of Zn marketed by Brazilian companies and obtain information related to fertilization and phytoavailability of micronutrients in corn plants to soil conditions of the western region of Parana state, promoting better fertilization recommendations for this place, the aim of this study was evaluate the productivity and yield components of corn fertilized with different sources and levels of Zn.

2. Material and methods

The experiment was conducted in the extreme west of Parana state (24[degrees] 27' S, 54[degrees] 09' W), in an area with 415 m of average altitude. The climate of the region is subtropical (Cfa) according to Koppen, without a definite dry season and presenting hot summers with trend towards concentration of rains in this season. The average annual temperature of the region is 21[degrees]C, with minimum of 14[grados]C and maximum 28[degrees]C.

The soil of the experimental site was classified as an Rhodic Eutrudox (Food and Agriculture Organization, 2006), with clayey texture (558.50 g [kg.sup.-1] of clay, 278.61 g [kg.sup.-1] of silt and 162, 89 g [kg.sup.-1] of sand).

Table 1 shows the results of the soil chemical analysis prior to the experiment at depths of 0 to 5 and 0 to 20 cm. The chemical analysis followed the manual of soil chemical analysis from the Agronomy Institute of Parana (Pavan et al., 1992).

The interpretation of the initial availability of Zn in soil ranked the concentrations of this element, for soils of Parana state, in the layer of 0 to 5 cm as good and for 0 to 20 cm as medium (Abreu et al., 2007).

The experimental design used in this experiment was a complete randomized block (CRB) in 8 x 4 factorial design, with three replications, being the treatments consisting of eight different sources of Zn and four different levels of Zn (0, 2, 4 and 6 kg [ha.sup.-1]), totaling 32 treatments and 96 experimental plots.

The eight sources of Zn used in this experiment are presented in the form of granules produced from two raw materials, which were the zinc oxide (ZnO) and the fritted trace elements (FTE), that are micronutrients fused with silicates at high temperatures, thus, the sources were classified as follow:

* Source A - ZnO granulated with 15% of Zn from company 1;

* Source B - ZnO granulated with 10% of Zn from company 2;

* Source C - FTE granulated with 15% of Zn from company 3;

* Source D - FTE granulated with 15% of Zn from company 4;

* Source E - FTE granulated with 10% of Zn from company 5;

* Source F - FTE granulated with 15% of Zn from company 6;

* Source G - ZnO granulated with 2% of Zn from company 1, but with different formulation.

* Source H - FTE granulated with 15% of Zn from company 7;

Thus, this study only varied levels of Zn, and fertilization with macronutrients was identical in all treatments, being applied at seeding, consisting of the elements nitrogen (N), phosphorus (P) and potassium (K).

For determination of the levels of N, P and K, based on the soil chemical analysis, it was used the recommendations of Coelho (2006). This way, it was applied 350 kg [ha.sup.-1] of a N:[P.sub.2][O.sub.5]:[K.sub.2]O formulation at 8:20:20 ratio. As source of macronutrients were used ammonium sulfate [[(N[H.sub.4]).sub.2]S[O.sub.4]] for N, superphosphate simple [Ca[([H.sub.2]P[O.sub.4]).sub.2] * [H.sub.2]O and CaS[O.sub.4].[H.sub.2]O] for P and potassium chloride (KCl) for K.

Each evaluation plot of the experiment consisted of five planting rows with 0.9 m spacing and 4.0 m length. As useful plot were used the three central rows, discarding 1.0 m from the edges as a border, providing a 5.4 [m.sup.2] floor area.

The pre-emergence weeds control was performed with the application of 2.0 L [ha.sup.-1] of 2,4-D and 5.0 L [ha.sup.-1] of glyphosate 15 days before sowing and 3.0 L [ha.sup.-1] of paraquat + diuron 7 days before sowing.

The seeds were sown on 28 October 2009, being used a corn hybrid cultivar 30F98 from Pioneer company, thus, six seeds were seeded per meter, aiming a 66666 plants per ha population. The seeds treatment against pests and diseases was performed with the insecticide fipronil (250 g [L.sup.-1]) at 50 mL per 50 kg of seeds and the fungicide carbendazin + thiram (100 g [L.sup.-1]) at 300 mL per 50 kg of seeds. Seven days after the full emergence of seedlings, November 11 2009, it was manually performed the application of Zn in their respective treatments.

The control of fall armyworm (Spodoptera frugiperda) was performed with the application of 50 mL [ha.sup.-1] of the insecticide spinosad (480 g [L.sup.-1]), being performed two applications for control. It was also performed hand weeding every 15 days for weed control. At 25 days after emergence (DAE) was performed a covering fertilization for N nutrient, being applied 100 kg [ha.sup.-1] of N as urea [[(N[H.sub.2]).sub.2]CO] (Coelho, 2006).

The material collection for foliar diagnosis of Zn concentration in plants was carried out at the onset of the female inflorescence (stage R1), reached at 61 DAE, and according recommendations of Ritchie et al. (2003). For this purpose, leaves were collected from the opposite side and below the upper cob of four randomly chosen plants within each plot. In the laboratory, leaves were washed with detergent and distilled and deionized water, afterwards the leaves midrib were discarded and these were dried in an oven of forced air circulation at 65[grados]C for 48 h. Subsequently, the leaves were crushed and stored in polyethylene bags cleaned properly and identified for further analysis.

To obtain the Zn contents in leaf tissue of corn plants was performed nitroperchloric digestion (Association of Official Analytical Chemists, 2005), using atomic absorption spectrometry, flame mode (AAS) (Welz and Sperling, 1999) to determine the concentrations of the element.

The experiment was ended at 119 DAE and the harvest of the useful plot was performed to determine productivity and yield components (weight of 1000 grain and cob weight). The cob weight was performed by weighing all the cobs collected and dividing by the total number of cobs, to determine the mass of 1000 grains was used the methodology described in Brazil (1992).

The statistical analysis of the results obtained in this work was performed with the aid of the SAS software. The data were subjected to variance analysis at 1 and 5% significance levels, the difference among sources was compared by the Tukey test at 5% probability and the fertilization levels effect was evaluated by regression analysis.

3. Results and discussion

The Zn content on leaf tissue of corn plants and productivity showed significant differences (p<0.05) in the interaction between the sources and levels of Zn. For the variables weight of 1000 grain and cob weight there was no significant difference (p>0.05).

The obtained results for the production components (weight of 1000 grains and cob weight) showing that the different sources and levels of Zn did not affect these variables. In other works related to Zn fertilization in corn, Ferreira et al. (2001) and Domingues et al. (2004) also did not obtain significant differences for the weight of 1000 grains in the varying levels of this micronutrient. According to Prado et al. (2008), the main functions of Zn in plants are: act as component of a large number of enzymes; act in the plant basic functions, such as metabolism of carbohydrates, proteins and phosphates; act in the formation of structures of auxin, RNA and ribosomes; as well in the phenols metabolism, in the increase of size and, cell multiplication and fertility of the pollen grain. Thus, this provides increased plant height, grain protein content, leaf number and production of forage and grains (Decaro et al., 1983).

The comparison between the means of Zn content on leaf tissue of the corn plants was showed in Table 2, were can be observed that source A was superior to the others, which in turn were similar among each other.

The fact of the source A is produced from ZnO, while sources C, D, E, F and H are formulated from FTE may explain the differences between them, since a study by Vale and Alcarde (2002), assessing the availability of different Zn sources in fertilizers, found that Zn present in oxide form provided much of this nutrient in relation to the FTE. This fact may be explained by the form in which the Zn is founded in these sources, where the form of ZnO has a high solubility in soil and availability to plants, while in the FTE form, the Zn is founded in poorly soluble forms, with slow release and lower than ZnO.

With respect to the sources A, B and G, all produced with ZnO, the difference could be explained by their solubility too, since they are formulated with different raw materials.

In an experiment evaluating the corn dry matter production as function of different Zn sources application, Amrani et al. (1999) concluded that the total Zn content guaranteed in the formulations did not match the nutrient availability for plants, even inferring that at least 50% of Zn contained in fertilizers must be soluble in water to ensure good availability of the element for plants. According to Alcarde and Rodella (1993), Brazilian law, through Decree 86.955 (Brazil, 1982), requires a minimum guarantee and the expression of the total content of each micronutrient in fertilizers marketed by companies, thus, the authors warn that such requirement allows the marketing of industrial byproducts that have trace elements with the minimum content required by law. However, these sources may not be in the chemical forms required in the legislation, nevertheless, some of these products may have poor agronomic efficiency, not being recommended for use as fertilizer.

The regression analysis for Zn contents on leaf tissue as function of the Zn levels from each source studied is shown in Figure 1, the interaction among treatments occurred to the Zn sources C, D, E and H, being that the mathematical model in which the data were best explained is the quadratic. For presentation of the equations and coefficients of determination for the models was developed an auxiliary table (Table 3).

By means of quadratic equations (Table 3) were obtained the Zn levels that provided the greatest amounts of this nutrient in corn plants, thus to the source A, the level of 3.48 kg [ha.sup.-1] provided the highest content of Zn the plants of all experiment, with 39.06 mg [kg.sup.-1] of Zn; for the source C was found that the level of 3.85 kg [ha.sup.-1] gave 31.01 mg [kg.sup.-1] of Zn to plants; the source E, with the level of 3.81 kg [ha.sup.-1] showed 28.92 mg [kg.sup.-1] of Zn, and finally, to the source H, it was found that the level of 3.95 kg [ha.sup.-1] provides a concentration of 28.18 mg [kg.sup.-1] of Zn. For the source D, the quadratic regression obtained was contrary to the others, making it impossible to calculate the level of maximum Zn accumulation by plants.

According to Rosolem and Franco (2000), the ideal levels of Zn in leaves of corn plants are between 20 and 70 mg [kg.sup.-1]. To Malavolta et al. (1997) and Coelho and Franca (1995) the optimal Zn level in corn leaves lies between 15 and 50 mg [kg.sup.-1] at culture flowering. In this experiment, all the means of Zn content on leaf tissue found were fall within the ideal range, including the maximum values obtained by the quadratic regression, demonstrating that the Zn sources studied provided good nutrition for corn plants without causing deficiency or toxicity to them.

The regression analysis of the corn productivity fertilized with different sources and levels (interaction) are showed in the Figure 2, where can be observed that occurred significant difference only for the sources A, D, F and H. Again, the data are better explained by quadratic regression.

By means of the regression equations were obtained the maximum crop productivities as function of Zn levels, however, Figueiredo et al. (2006) state that the level that best shows economy and efficiency of a fertilizer is usually between 80 to 100% of the maximum productivity level. Thus, it was considered as maximum level of economic productivity (MEP) the one that provided 90% of maximum productivity (Raij, 1981).

For source A, the Zn level that allowed the MEP was 3.17 kg [ha.sup.-1] (8487.71 kg [ha.sup.-1] of grains), as to the source F, the level was 2.52 kg [ha.sup.-1] (7661.54 kg [ha.sup.-1] of grains), and finally to the source H, the ME-1P level was 3.55 kg [ha.sup.-1], providing 7832.20 kg [ha.sup.-1] of grains.

Likewise that Zn contents in leaf tissue, for productivity, the source D showed opposite behavior to others, not being possible to determine the Zn level for maximum productivity, the level of 6.0 kg [ha.sup.-1] of source D promoted 8268.30 kg [ha.sup.-1] of grains.

The fact that the source D provides the best results only in higher levels allows us to infer two assumptions: this source has a high solubility, which would result in a quick release and/or consequential loss by leaching, thus making difficult the nutrient absorption at low levels. However, this first theory can be discarded due to the soil has high clay content (558.50 g [kg.sup.-1]) and a high cation exchange capacity (CEC) (12.55 [cmol.sub.c] [dm.sup.-3]). The second hypothesis justifies the opposite, the source has low solubility, and will only provide adequate nutrient at high levels, which may have been manufactured from raw materials of inferior quality.

There are several studies related to level and/or sources of Zn in the literature (Korndorfer et al., 1995; Ferreira et al. 2001; Furlani et al. 2005; Lana et al., 2007), some obtained responses in corn productivity while others did not. Data comparison is very specific and complex, as if dealing with micronutrients, were the initial values in soil are of great importance, this way, responses will be different in each study. However, concerning corn fertilization with Zn, Souza et al. (1998) argue that there is no advantage in applying Zn levels higher than 5.0 kg [ha.sup.-1] in Brazilian soils, confirming the results of this experiment to the sources with best performance, where it is not justified the fertilization at Zn levels higher than 4.0 kg [ha.sup.-1].

In a practical view, the present results demonstrate the need for evaluating the nutritional status of the soil before fertilization recommendation, as well the requirement from farmers that the fertilizer sold in Brazil had good quality, because only the guarantee of the minimum contents of nutrient is not enough for a good solubility and availability to plants.

Is also important highlight that low-quality raw materials, besides do not provide the nutrients properly, can provide significant amounts of contaminants, such as toxic heavy metals, that can cause significant environmental impacts.

4. Conclusions

Among sources studied, the Zn source from company 1 (source A) provided greater Zn availability to corn plants of the experiment, considered thus superior to the others.

Fertilizers produced from raw materials of low quality have low nutrient availability to plants, and thus, their use should not be recommended.

In this experiment, and for most soils in western of Parana, it is justified the Zn fertilization at 4.0 kg [ha.sup.-1] maximum level.



DOI: 10.5261/2011.GEN3.07

Received: 01 June 2011

Accepted: 29 July 2011


To the colleague Daniel Schwantes who spared no efforts to carry out this work and the CAPES funding agency for granting the master scholarship.


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Nacke, H. *, Goncalves Junior, A. C., Stangarlin, J. R., Schwantes, D., Strey, L., Nava, I. A.

Universidade Estadual do Oeste do Parana, Centro de Ciencias Agrarias, Rua Pernambuco 1777, Marechal Candido Rondon, PR, CEP: 85960-000.

* Corresponding author:
Table 1. Chemical analysis of the Rhodic Eutrudox used in the
experiment at 0-5 and 0-20 cm depths

                          [K.sup.+]   [Ca.sup.2+]   [Mg.sup.2+]
Sample   pH

0-5           5.10          0.66         6.36          1.07
0-20          4.83          0.42         4.34          0.99

                           H+Al       SB      CEC          OM
Sample   pH
                          --[cmol.sub.c][dm.sup.-3]-- g [dm.sup.-3]

0-5           5.10         4.46      8.09    12.55        25.97
0-20          4.83         5.79      5.75    11.54        20.51

                            P      Cu      Zn     Fe       Mn      V%
Sample   pH
                                          --mg [dm.sup.-3]--        %

0-5           5.10        24.09   8.10    2.01   38.77   162.00   64.46
0-20          4.83        10.58   12.50   1.44   76.65   261.00   49.83

H + Al (potential acidity); SB (sum of bases); CEC (cation exchange
capacity); OM (organic matter), V% (saturation by bases), Cu, Zn, Fe
and Mn extracted by Mehlich-1.

Table 2. Means of Zn contents in leaf tissue of corn plants fertilized
with different Zn sources

Zn source   Zn content (mg [kg.sup.-1])

source A              31.89 A
source B              26.41 B
source C              26.46 B
source D              27.14 B
source E              25.36 B
source F              25.00 B
source G              23.84 B
source H              24.88 B
M.S.D.                 4.13

Means followed by different letters differ by the Tukey test at 5%
probability; M.S.D--minimum significant difference

Table 3. Quadratic regression equations and coefficient of
determination for Zn contents on leaf and productivity of corn crop
fertilized with different sources and levels of Zn

Variable   Zn source          Quadratic regression equation

Zn         source A     [Zn] = -5.483[x.sup.2] + 30.073x - 2.172
           source C     [Zn] = -3.178[x.sup.2] + 18.584x + 3.833
           source D      [Zn] = 1.202[x.sup.2] - 3.708x + 27.394
           source E     [Zn] = -2.510[x.sup.2] + 14.578x + 7.743
           source H     [Zn] = -2.235[x.sup.2] + 13.301x + 8.393
PROD       source A   PROD = -785.38[x.sup.2] + 4331.78x + 2514.78
           source D    PROD = 103.42[x.sup.2] - 344.97x + 6615.00
           source F   PROD = -662.91[x.sup.2] + 3182.91x + 3854.07
           source H   PROD = -432.49[x.sup.2] + 2567.97x + 4036.86

Variable   Zn source   [R.sup.2]

Zn         source A     75.80%
           source C     98.14%
           source D     95.12%
           source E     73.20%
           source H     99.79%
PROD       source A     95.80%
           source D     99.91%
           source F     85.65%
           source H     96.22%

[R.sup.2] (determination coefficient of the quadratic equation); R
(correlation coefficient of the quadratic equation); [ZN] (Zn content
on the leaf tissue of corn plants evaluated at the R1 growth stage);
PROD -productivity of the corn crop.
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Author:Nacke, H.; Goncalves, A.C., Jr.; Stangarlin, J.R.; Schwantes, D.; Strey, L.; Nava, I.A.
Publication:Spanish Journal of Rural Development
Date:Jul 1, 2011
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