Top dressing in corn

The application of nitrogen sources can be a difference in increasing productivity in corn crops. But in order to minimize losses from the applied fertilizer, it is necessary to use strategies and technology, as is the case of coating the nutrient with a protective layer, which allows controlled release.

The application of nitrogen sources in corn crops can be a differentiator for expressing the productive potential of the sown hybrid. Nitrogen losses from the application of urea can occur in different ways, being leached, volatilized and even immobilized during the decomposition of plant residues left by previous crops.

With the technological development applied to the agricultural sector, technologies have emerged to protect urea granules, in order to minimize the losses that occur after covering this source of nitrogen. This coverage tends to control the release of the nutrient, allowing its absorption for a longer period when compared to urea without coverage, which offers all the nitrogen applied at once.

According to data from Conab (2014), total corn production in Goiás in the 13/14 harvest averaged 107sc/ha. Nitrogen (N) is the nutrient absorbed in the greatest quantities by corn and the one that most influences grain yield (SILVA et. al., 2005). Urea has the advantage of high concentration of nitrogen, easy handling, lower cost per kilo of nitrogen, but presents high losses of this element due to volatilization (PRIMAVESI et al., 2004). Inadequate use of N can cause environmental damage, such as contamination of surface and groundwater by nitrate, due to losses through erosion and leaching (SIMS et. al, 1998). An alternative to reduce these losses would be to protect the urea granule with less hygroscopic products that allow it to be applied to the soil surface, which could delay its release (BONO; SETTI; SPEKKEN, 2006).

With the objective of evaluating the application of urea with and without coating in two doses of total N, applied as top dressing in corn crops, an experiment was conducted in the experimental area of ​​IFGoiano, Câmpus Rio Verde. A randomized block design in a 4x2 factorial was used, consisting of seven treatments with four replications: control (C) without application of N, urea (U), polymer-coated urea (URP) and sulfur-coated urea (URS), with two doses of total N: 75 kg/ ha and 150 kg/ ha.

The study was conducted on soil under cerrado. Table 1 presents the results of the chemical analysis of the soil collected in the 0cm-20cm layer. 

According to SOUZA et.al (2004), for soils under cerrado in a layer of 0cm-20cm, the value found for P and K is in the content range known as low. Therefore, correction was carried out with KCl at an application rate of 120kg/K₂O/ ha for potassium correction and 120kg/ P were used₂O_5/ ha of triple super phosphate (SFT) applied by broadcast as a source of phosphorus.

The experimental design used was a randomized block design with four replications in a 4x2 factorial scheme, with four sources of nitrogen (control [C] without application of N, urea [U], polymer coated urea [URP] and sulfur-coated urea [URS]), with two doses of total N (75Kg/ ha and 150Kg/ ha).

Corn planting was carried out with Agroeste AS1598PRO2 seeds, VTPRO 2 version within the ideal planting window, recommended by the company supplying the seeds.

The spacing used for sowing was 0,45m between plants and also 0,45m between rows with an average of 3 plants per meter and a total of 60.000 plants per hectare. For each plot, 6 rows of 6 meters each were planted, totaling an area of ​​16,20m².

Table 2 presents the nutrient portion that comprises the total value of each product used as a source of nitrogen.

The application time was determined by the number of leaves per plant. The treatments were applied between phenological stages V4 and V6, following recommendations from Embrapa (2011) to cover corn with nitrogen between stages V4 and V8.

The supply of N to the corn crop at the application stage was sufficient to increase productivity in relation to the control. It can be seen in Table 3 that there was a significant difference using the Tukey test at 5% probability for the productivity variable, where the treatments that used nitrogen fertilizer were statistically superior to the control treatment.

For the dose variable, it can be seen in Table 3 that there was no significant difference using the Tukey test at 5%, with no statistical difference for productivity in kg/ha regardless of the dose or source of nitrogen fertilizer used. A similar result was obtained by VALDERRAMA, et al. (2014), where the Corn productivity was not affected by N sources, demonstrating that ureas coated with polymers in different compositions and concentrations did not stand out in relation to conventional urea.

CASAGRANDE & FORNASIERI FILHO (2002) obtained control productivity of 4.592 kg/ha and attributed this effect to the supply of N by soil organic matter, whose value was 27 g dm^-3. In the present work, the organic matter content observed in the soil before planting was 30,1 g dm^-3, so this effect may also have occurred.

It was observed that URP at a dose of 150 kg N/ha provided greater grain production, which is probably due to the full use of the N released in the application followed by a subsequent gradual supply. For U, the dose of 75 kg N/ha was ideal at the time of top dressing application, reducing losses due to volatilization. For U at a dose of 150 kg N/ha, it is assumed that the high availability of N through fertilization, associated with the N released from the decomposition of organic matter, may have resulted in a longer period of plant permanence in the vegetative phase, denoted by the higher average height of plants between treatments (2,39m), thereby delaying the reproductive phase.

For the URS 150 Kg N/ ha treatment, similarity is observed with that suggested for URP 150 Kg N/ ha^.  However, possibly because the product contains a layer of sulfur and a layer of wax, there may have been a delay in the initial release of N, with an increase in this release in subsequent weeks.

Observing the variables Productivity of Bags More than the Control Treatment (PSTC) and %STC (percentage of bags more than the control treatment) it is possible to observe more clearly the increase in productivity over the control treatment. It is also possible to verify the differences between each treatment that used different doses and sources of nitrogen fertilizer, even though there was no significant difference using the Tukey test at 5%. It is observed that U 75 had a higher production than U 150. This must be attributed to the amount of nutrient that was offered at once to the plant, saturating its absorption capacity. On the other hand, URP 150 obtained the highest production of the treatments, which is due to its ability to produce a controlled release of nitrogen. In the first instance, the released dose supplied the plants that were in the development phase, and the second part released by this source must have been absorbed in the reproductive phase. URP 75 probably acted in the same way. However, in the first instance it released a much smaller amount of N than URP 150. As for URS, along with the release of N, there is also the release of S, which is also an essential nutrient for the plant. The URS 150 achieved a greater increase in production when compared to the URS 75.

Under the conditions of the experiment, it is possible to conclude that the use of nitrogen fertilizers resulted in an increase in the productivity of corn grains. Controlled release sources were not satisfactory for application between phenological stages V4 to V6, as they provided results similar to conventional urea at the same doses. Successor research is suggested by varying the application stage of coated nitrogen sources to better position the technology.

Fernando Rezende Corrêa, Daivid Vieira Lima, Instituto Federal Goiano Campus Rio Verde; Daniel Arisawa Capelari, Renovar Agrícola; Orlando Homero Ribeiro Neto, Comnagro; Agnaldo Eleuterio Silva, Monsanto; Ludmilla Ribeiro da Rocha Gomes, University of Rio Verde

Article published in issue 204 of Cultivar Grandes Culturas.