importance of nitrogen fertilization for corn cultivation
The application of nitrogen (N) to corn is considered an important practice for the crop. Corn is highly responsive to this element, and adequate nitrogen availability is essential to achieve high yields, both in terms of biomass production and final grain production. Therefore, nitrogen fertilization is one of the most important agricultural practices to maximize corn productivity.
N is an important structural agent in plants, a constituent of chlorophyll, proteins and amino acids, in addition to being involved in the production of hormones. The element also has a great influence on the photosynthesis process and several other characteristics that define it as one of the main macronutrients for plants.
Furthermore, nitrogen plays a crucial role in plant development and growth. In corn cultivation, it is the nutrient most accumulated and exported by the grains, and, on average, 17 kg/ha to 23 kg/ha of nitrogen are removed for each ton of harvested grains (Coelho et al., 2011 apud Embrapa, 2021). This high demand and removal of nitrogen further highlights its indispensable importance in corn production.
Nitrogen deficiency symptoms
In case of N deficiency, the crop may present: reduced growth, lower quality and quantity of carbohydrates, proteins and fats and, above all, becomes more susceptible to attack by pests and diseases.
Some common symptoms seen in the field are chlorosis of the oldest leaves (base of the plant), in a “V” shape, followed by necrosis (as represented in figure 1) and reduction in ear size, which will consequently result in in crop productivity losses.
Ways of nitrogen absorption by plants
N is transported to the roots of plants by mass flow, where the nutrient moves in the soil through the existing water flow and is absorbed by plants in the forms of ammonium (NH4+) and nitrate (NO3-), forms of N that they represent less than 2% of the total nitrogen in the soil.
In other words, this indicates that most of the nitrogen (N) present in the soil is in organic form, which means that it can be gradually mineralized throughout the crop's growth cycle, due to microbial activity. As a result, it is not readily available to plants in its entirety, which explains the importance of incorporating N into the production environment.
Possible sources of nitrogen input in our cultivation
N in a production system can come through biological fixation and/or nutrient cycling through cover crops, mineralization of organic matter, application of organic fertilizers such as swine manure, mineral application of ammonium sulfate (20% N and 22-24% S), ammonium nitrate (32% N), urea (45% N) among others. The main and most used being urea (45% of N), however, for this N is quite susceptible to losses, mainly due to volatilization of ammonia (NH3) if applied and the climate conditions are favorable to this loss.
Main precautions that must be taken during application
It is essential to pay attention to soil moisture and urea application times to optimize the efficient use of nitrogen (N). In this sense, it is advisable to apply it to soils with adequate humidity or before rain of moderate to low intensity. It is preferable to carry out this operation in the afternoon, as the peak of ammonia transformation occurs approximately 6 hours after the application of urea, coinciding with the night period, when there is no direct solar radiation and temperatures are milder. These factors contribute to minimizing N volatilization losses.
On the other hand, it is important to avoid applying urea before heavy rainfall and during periods of strong sunlight. In soil conditions with lower humidity and high radiation, ammonia losses through volatilization can be significant, reaching more than 50% of the N applied. Therefore, the timing and conditions of application play a critical role in the effectiveness of urea fertilizer.
What criteria can be used to define the amounts of nitrogen for best results?
To determine the appropriate amounts of nitrogen to be applied, it is essential to carry out a soil analysis in the area intended for cultivation. According to guidelines in the Fertilization and Liming Manual for the states of Rio Grande do Sul and Santa Catarina (2016), the amount of nitrogen to be applied to the crop is determined based on several factors, including the organic matter content of the soil, which it is obtained through soil analysis, as well as considering the previously cultivated crop and yield expectations. Normally, the nitrogen dose is divided between a portion applied at the base, close to the sowing line, and the remainder applied as cover throughout the crop cycle. This process aims to ensure adequate nutrition for the corn throughout its development.
Still according to the Manual, in the direct planting system, it is suggested to apply at the base, next to the sowing line, from 20 kg to 40 kg of N ha-1, when cultivation is in an area with grass residues and between 10 kg and 20 kg of N ha-1 when cultivated in an area with legume residues.
Best times to apply nitrogen top dressing in corn crops
For the application of N in top dressing, it is suggested that this be carried out in two moments to enable better synchronism between the N available in the soil and the plants' demand, and it is recommended that 50% of the dose be applied in top dressing between the vegetative stages. V4 to V6 and the other 50% during stages V8 and V9. It can also be applied once between stages V4 to V6, with the number of applications mainly defined by the dynamics of machinery and people within the property.
The increase in the availability of this nutrient in the soil at stages V4 to V6 is due to the fact that the crop at this stage defines its productive potential. During the V8 and V9 stages, the crop defines the number of rows per ear and the size of the ear. Applications carried out outside the recommended season can enhance biomass production, but not final grain productivity in an economically viable way.
Has foliar nitrogen supplementation resulted in corn crops?
Foliar nitrogen (N) supplementation in corn crops, as a complement to topdressing N application, can be a strategy to address possible deficiencies of this element during the grain filling phase, as highlighted by Pacentchuk et al. (2014). However, in studies conducted at Fazenda Santa Cruz, located in the municipality of Guarapuava, in the state of Paraná, the same authors observed that the application of supplemental N via foliar means presents itself as a viable alternative to increase the final grain productivity in soybean crops. , corn and beans.
Although they did not observe a significant response in corn productivity in relation to the application of nitrogen foliar fertilizer, they noted that this response was quadratic in nature, that is, non-linear, with the increase in the dose of nitrogen foliar fertilizer. The response was more pronounced, reaching an increase of 5% when the application occurred in the V13 phase of the plant, and 1% in applications carried out during pre-tasseling and flowering. This suggests that the effectiveness of foliar N supplementation may vary depending on the stage of crop development and the dose applied, highlighting the importance of carefully considering these factors when making decisions about foliar fertilization in corn.
In the field, foliar nitrogen supplementation to top dressing in corn is not a common practice. However, if this approach is adopted, it is crucial to closely monitor the concentration used in order to avoid potential problems related to phytotoxicity.
By: Alfredo Henrique Suptiz and Caetano Rocha, academics from the Agronomy course at UFSM, Frederico Westphalen campus, members of the Tutorial Education Program (PET) Agricultural Sciences, under the supervision of the tutor, professor Dr. Claudir José Basso.
BIBLIOGRAPHIC REFERENCES:
EMBRAPA. Morphological and Productive Parameters of Corn Culture Inoculated with Plant Growth-Promoting Bacteria in Teresina, PI. Available at: https://ainfo.cnptia.embrapa.br/digital/bitstream/item/226246/1/ParametrosMorfologicosProdutivosMilhoInoculadoBP131.2021.pdf. Accessed on: Aug 5th. 2023
MANUAL. Fertilization and liming for the States of Rio Grande do Sul and Santa Catarina. 11 ed. Brazilian Society of Soil Science, Southern Regional Center, Soil Chemistry and Fertility Commission, 2006. 125 to 127 p.
PACENTCHUK et al. Supplementary nitrogen via foliar use in corn, soybean and bean crops: doses and phenological stages of application. Plantio Direto Magazine, 2014, ed. 142/143. Available at: https://www.plantiodireto.com.br/storage/files/142-143/5.pdf. Accessed on: Aug 7th. 2023.
