Wheat plays a key role in the global diet, being one of the main crops responsible for meeting the food needs of the world today. Therefore, the demand for the grain has increased significantly, which puts producers in the face of the challenge of finding innovative and sustainable strategies to increase production without compromising quality.
When it comes to quality productivity, several factors are involved, but one of the most important is the adequate supply of nutrients throughout the crop's growth cycle. In this article, we're going to focus specifically on one essential nutrient, nitrogen (N).
Considered a primary macronutrient, according to Bona et al. (2016), nitrogen performs several crucial functions in wheat plants, in addition to being one of the most demanded by them. It is present in the composition of the chlorophyll molecule, as well as in the carbohydrates that make up the plant. This participation in the molecular structure is fundamental for the development of photosynthetic activity, ensuring that it occurs efficiently.
Precisely for this reason, institutions such as Embrapa recommend that it be necessary to adopt agricultural practices that guarantee an efficient and balanced application of nitrogenous fertilizers, taking into account the specific needs of wheat plants at each stage of growth.
Nitrogen in the soil
Organic matter is the main natural source of nitrogen in the soil, however, this nitrogen is not readily available to plants. Its release occurs slowly and depends entirely on the microbial activity of the soil, which becomes a problem when it does not have ideal amounts of organic matter or an active microbiota. In addition to all this, the nutrient has high mobility in the soil profile, which means that the producer cannot depend exclusively on its natural supply.
As a curiosity, the soybean crop has the unique ability to fix atmospheric nitrogen and use it for its basic functions. In the case of wheat, the situation is different, and fertilization becomes the best way to be followed to meet the N needs of this crop.
How to identify N deficiency in your crop?
In cases of disability, the main form of identification is through the sheets. Because it is a nutrient directly linked to chlorophyll, when low, the plant reduces the levels in the leaves and begins to lose the characteristic green, showing chlorosis. In addition, as it is a nutrient with high mobility in the phloem, these symptoms are initially noticed in older leaves.
There are also other symptoms, such as lower tillering, low number of leaves and, mainly, increased susceptibility to attacks by pests and diseases.
When the deficiency becomes visually evident in plants, it means that productivity has already been compromised. However, to determine the appropriate amount and time to apply nitrogen to a wheat crop, it is necessary to resort to other strategies, as soil analysis does not provide direct information on nitrogen content.
Nitrogen in soil analysis?
Nitrogen, unlike other nutrients, is not included in the analysis results because it is a very dynamic element in the soil and for some other reasons:
its availability is directly related to microbial activity and the decomposition of organic matter;
it is highly soluble in water and can easily move within the soil profile, making its measurement more complex.
Rather than directly measuring soil nitrogen content, chemical analysis usually focuses on determining other essential nutrients such as phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg) and various micronutrients, for example. be more stable and less subject to changes considered rapid on the ground. However, the good news is that nitrogen levels can be estimated indirectly based on other characteristics such as soil organic matter content.
For this, it is necessary to carry out specific tests, such as the determination of mineralized nitrogen or the evaluation of microbial activity – such tests help to provide information about the soil's ability to make nitrogen available to plants. This information can be useful to adjust management practices, mainly as the direction of nitrogen fertilization.
Parallel to this perspective, there are some agronomic approaches that contribute to determine the need for N and the ideal moment of application in a wheat crop. They consider:
the already known nutritional demand of the wheat crop;
the expected productivity of the crop;
which management practices are historically practiced on the farm.
Some of the tools that can be used for this recommendation:
Leaf analysis: the collection and analysis of leaf tissue samples can provide information on nitrogen levels in plants;
Crop demand forecast: currently, with so much research, we can, based on the crop development phase, recommend nitrogen fertilization and plan the application according to the productivity goal;
Exclusive recommendation models: there are technological models available that integrate NDVI data and images on the crop, integrating productivity history, soil characteristics and climate, to understand and generate personalized N recommendations for your crop.
Grower Tip: It is important to consult an agronomist for specific guidance based on local conditions, management practices and desired yield goals.
Understanding that your crop cannot fail to be fertilized with N, when should you apply the fertilizer?
Nitrogen fertilization in wheat is usually carried out at specific times of the crop's growth cycle, which are:
Planting fertilization: a portion of nitrogen can be applied at the time of planting or before planting, incorporated into the soil. This helps provide initial nutrients to the plant's roots as they begin to become established and ensures an excellent initial start.
Top dressing: Most nitrogen fertilization on wheat is done as a top dressing application after the plants emerge. This application is usually divided into two or more installments, about 3 to 4 weeks apart. This allows nitrogen to be supplied to the plants as their growth needs increase throughout the cycle.
In studies by Embrapa Trigo, also by researcher Fabiano Daniel De Bona, this division is ideal, the first of which consists of applying, on average, 15 to 20 kg of N/ha in the sowing line. The remainder of the fertilizer should be applied as cover during the tillering period. He concludes that these two phases are considered essential for plant growth, mainly to guarantee the formation of the leaf area and grain filling.
It is important to point out that nitrogen fertilization has a perceptible visual impact on the productivity and health of wheat crops, since its effects can be easily observed by the color of the leaves.
What is the best font to use?
There are several sources of nitrogen currently available on the market. Some of the main ones include:
Urea: one of the most popular sources. It is solid and has a concentration of 46% N. In addition, its ease of handling is another competitive advantage compared to other sources.
Ammonium nitrate: highly soluble in water, provides N in both nitrate and ammonium forms, and is also a popular source of nitrogen. It has a high concentration, around 34%, and is often used in crops that demand rapid nitrogen availability.
Ammonium sulfate: is a fertilizer that supplies nitrogen in the form of ammonium, along with sulfur. It is highly recommended for alkaline soils.
Calcium Nitrite: This is a less common fertilizer, but is still used to provide nitrogen in the form of nitrate. It also provides calcium to the crop.
Grower Tip: When selecting the most suitable fertilizer for your wheat crop, it is important to consider the specific characteristics of each nitrogen source, such as release rate, solubility, volatilization and interaction with other nutrients in the soil.
Currently, there are technologies such as stabilized and controlled-release fertilizers, which aim to provide nitrogen in a gradual and prolonged way throughout the crop cycle. Such products focus on reducing losses and increasing efficiency of use, such as NBPT stabilized urea. Check out the benefits:
Reduction of nitrogen losses: we know that urea is susceptible to nitrogen losses in the form of gaseous ammonia by volatilization, especially when applied on the surface and not incorporated into the soil. NBPT is precisely a stabilizer that inhibits this volatilization, reducing nitrogen losses and increasing the efficiency of its fertilization.
Greater Availability: NBPT can also help convert urea into a more stable form of nitrogen. This means that it will remain available to plants for an extended period, contributing to more efficient uptake and preventing excessive release.
Improved uniformity of distribution: Urea stabilized with NBPT is usually granulated or coated, which improves uniformity of distribution during application. This avoids variations in the amount of nitrogen applied in different areas of the field, ensuring more balanced nutrition.
Sustainability: by reducing nitrogen losses, it contributes to minimizing the risk of water contamination.
It is always recommended to consult a crop nutrition expert for guidance appropriate to your specific context.
