Pastures, whether native or planted in winter or summer, play a key role in animal production in extensive, semi-extensive or intensive systems in Brazil. Pasture quality is reflected in animal weight conversion and milk production. Pastures occupy almost half of the country's rural establishments and feed more than 200 million animals, including cattle, sheep, goats, horses and buffaloes (EMBRAPA).
Brazil has the second largest cattle herd in the world, corresponding to 18% of the world herd, second only to India (MALAFAIA et al., 2019). Beef cattle production in Brazil is predominantly explored in the extensive system under a pasture regime, with native and/or cultivated pastures, with production distributed in three distinct phases: breeding, rearing and fattening (SVERSUTTI; YADA, 2019). In addition, it is among the five largest milk producers in the world, with national production of 35.3 billion liters of milk in 2021 (ANDRADE et al., 2023).
Good pasture production, regardless of the crop, is closely related to maintaining the soil-plant-animal balance, since all exported nutrients must be replaced in the system, aiming at its longevity (EDUCAPOINT, 2020).
Characteristics of pasture types
To the native pastures are the type of spontaneous vegetation that has some type of forage value, this type of vegetation grows after the destruction of the original vegetation. Native pastures with significant economic value for beef production in Brazil are located in different ecosystems in the North, Northeast, Central-West and South regions. Due to the great variability in the physiognomy and floristic composition of the different ecosystems, native pastures vary from a herbaceous extract with grasses and legumes to a shrubby tree with medium-sized plants (SVERSUTTI; YADA, 2019).
When natural pastures are affected in terms of their quantitative and qualitative potential or their persistence, we can then resort to pasture improvement techniques. These techniques include adequate soil correction and fertilization, introduction of species through techniques that do not disturb the existing herbaceous substrate, such as direct seeding, and the adoption of correct management with the aim of having an improved natural pasture (FREIXIAL; BARROS, 2012).
To the cultivated pastures (winter or summer) are composed of exotic or native species, where the original vegetation no longer exists (SVERSUTTI; YADA, 2019). They are normally included in agronomically coherent rotations with other crops, therefore having a shorter and more variable duration, depending on the objectives and criteria adopted for the rotation (FREIXIAL; BARROS, 2012).
In the winter pastures, the cultivation of winter forage plants is favorable in the southern region of Brazil (FERRAZZA et al, 2013). Examples of annual winter forages that have been used to meet the animals' food needs are ryegrass, black and white oats, rye, triticale and wheat (NICOLOSO; LANZANOVA; LOVATO, 2006).
Brazil is a country with a predominantly tropical climate, marked by high temperatures during the summer. And for summer pastures, the types are diverse. And among them, we can mention: sorghums for cutting and/or grazing which are interspecific hybrids of Sorghum bicolor x Sudanese sorghum (Sudan grass), millet (Pennisetum americanum), aruana grass (Panicum maximum cv. Aruana), Aries grass (Panicum maximum cv. Aries) and the Brachiarias (Urochloa brizantha – old Brachiaria brizantha – cv. Xaraes) (EMBRAPA).
Importance of fertilization for pastures
For Santos (2010), the most widespread effect of fertilization in pastures consists of increasing forage production per unit area. This makes it common to associate pasture fertilization with high-tech or intensive systems. In intensive production systems based on the use of pastures, fertilization is a management action that is generally present and fundamental (SANTOS, 2010). As an example of the use of fertilization to increase animal production in pastures, we can mention the work conducted by Moreira (2000) in the summer, which evaluated the primary and secondary production of Brachiaria decumbens cv. Basilisk (signal grass) fertilized with four nitrogen rates (75, 150, 225 and 300 kg/ha of N). Signal grass was managed with variable stocking rates in order to maintain the average pasture height at approximately 20 cm. In this management, pastures fertilized with higher N rates showed a higher growth rate and, consequently, higher forage accumulation, which made it necessary to increase the pasture stocking rate to maintain the average pasture height within the desired target (20 cm). As a result, there was higher animal production per unit area in those pastures fertilized with higher nitrogen rates, without compromising animal performance (SANTOS, 2010).
Among the main management strategies (Figure 1) are nitrogen fertilization and grazing intensity (height), since both, when properly guided, increase forage yield and improve crop performance sown in succession (ASSMANN et al., 2003). It is known that different grazing intensities (CARVALHO et al., 2010) and nitrogen fertilization strategies (LUPATINI et al., 2013) alter the pasture structure, affecting the ingestive behavior of grazing animals and, consequently, animal productivity in crop-livestock integration systems.
Figure 1- Possible objectives to be achieved with pasture fertilization. Source: Santos, 2010.
Fertilization systems are based on biological nutrient cycling, which is understood as the flow or movement of nutrients in the different compartments of the pasture ecosystem (soil-plant-animal-atmosphere) (DE SÁ SOUZA et al., 2028). Nutrient availability is determined by molecular changes for use by soil microbiota, plant and animal species within the pasture (DUBEUX JR et al., 2006). When we talk about a crop rotation system, the aim is to achieve maximum efficiency in the use of nutrients, reduce inputs, avoid losses and maintain soil fertility in the long term (BARRIGA, 2019). Furthermore, it must consider all crops involved and that nutrient transfer is a key component for the success of the production system (ASSMANN; SOARES, 2016).
For Barriga (2019), fertilization systems aim to supply nutrients to winter crops, with the aim that cycling also promotes their release to summer crops. The aim is to nitrogen fertilization, in the pasture phase, which is normally in winter, since at this time the cost of the input is lower, in addition, due to the lower temperatures, lower losses of N through volatilization are expected. In addition to the temperature factor, because the pasture is conducted with smaller spacing, with the presence of roots and soil cover, there is a greater capacity for absorption of the nutrient, which allows maximizing the use of nitrogen when applied to the forage crop during the winter (ASSMANN, 2008; DE BORTOLLI, 2016). For example, while in September a corn crop has 7 plants per m2, a ryegrass pasture can have 4600 tillers per m2 (PONTES et al., 2003), which allows the interception of nitrogen molecules by the roots and their absorption, avoiding losses due to leaching.
As well as nitrogen we can mention match which plays an important role in the initial start-up of plants and in maximizing tillering, combined with its role in energy metabolism (PEREIRA et al., 2018). And the potassium which is present in several processes in the plant, with emphasis on osmotic regulation and stomatal movements.
Although it is not customary to fertilize pastures with specific sources of sulfur (S), this nutrient is closely linked to N metabolism and must be taken into account when fertilizing (PEREIRA et al., 2018).
The cultivation of pastures on soils poor in fertility, with liming frequent without the proper calculations and the increase in productivity are favoring the emergence of deficiency micronutrients (RAIJ et al., 1997 apud PEREIRA, 2018). In this sense, forages are unable to express their maximum productive potential, as micronutrients perform vital functions in the plant, such as the composition of compounds responsible for metabolic and phenological processes, enzyme activators and even in the production and regulation of phytohormones (PEREIRA et al., 2018).
Another important factor is the maintenance fertilization since the pastures are classified as perennial crops, therefore, they remain in the field for a longer period of time; therefore, it is recommended maintenance fertilization, so that nutrients continue to be supplied to the plants in adequate quantities to achieve the desired biomass production.
The atmosphere, soil, plant species and grazing animals are considered the largest nitrogen (N) compartments within pasture ecosystems, where biotic (vegetation, animals and microorganisms) and abiotic (humidity and radiant energy) factors are responsible for its movement in the different compartments (DUBEUX JR et al., 2007). In most agricultural lands in the world, nitrogen is considered the most limiting nutrient for crops, due to its low availability in tropical regions, contributing to increased pasture degradation (VENDRAMINI et al., 2007).
Nutrients with high mobility in the soil, such as nitrogen and potassium, are more easily leached, especially in deeper soils, and are translocated by rainwater, making it difficult for the root systems of many crops to access nutrients. Volatilization, a process generally observed with nitrogen, occurs through denitrification (TEIXEIRA, 2010).
Among the main factors that interfere with nitrogen dynamics, the carbon:nitrogen (C:N) ratio of soil organic matter (SOM) deserves to be highlighted, which determines the decomposition rate, as well as interferes with the mineralization or immobilization of nitrogen by soil microbiota (Figure 2) (DE SÁ SOUZA et al, 2018). Troeh & Thompson (2007) explained that when microbial activity acts on the decomposition of SOM, inorganic forms of elements are released, a process known as mineralization. However, when inorganic ions are converted into organic forms, it is called immobilization (TROEH & THOMPSON, 2007). These authors also stated that a large part of nitrogen immobilization occurs due to the fact that soil microorganisms need nitrogen to synthesize proteins, concluding that the introduction of decomposable materials into the soil with low concentrations of this nutrient will result in greater immobilization of the same (DE SÁ SOUZA et al, 2018).
Pastures play a fundamental role in both the movement and content of carbon in the soil. According to Braga (2006), approximately 20% of the carbon circulation on the planet and 12% of the carbon stored in the soil come from pastures.
Figure 2. Nitrogen cycle in a cropping system. Source: ILSA
Nitrogen applied in winter enables higher pasture and animal product yields, remaining in the system and being able to be used by the subsequent crop. This effect characterizes nutrient cycling and allows the practice of fertilization of the production system and not restricted only to the crop in question (BARRIGA, 2019). There is better use of nutrients, there is a reduction in production costs as well as lower environmental impacts considering the dynamics of the nutrient in a crop production system (SARTOR, 2014).
Sandini et al. (2011) state that the use of N in winter pastures contributes to increased forage production, the production of grazing animals with greater weight gain and increased animal load, in addition to the grain production of subsequent crops. Nitrogen fertilization has a direct effect on the increase in forage production as well as the carrying capacity of the pasture (DE BORTOLLI, 2016). Correa et al. (2006) showed that the application of 200 kg per ha of N promoted an increase in the carrying capacity of the pasture, with an animal load equivalent to two hectares without fertilization. Follmann (2015) states that nitrogen applied to pasture will provide an increase in plant production that will be consumed by animals, resulting in greater milk or meat production, also promoting greater animal carrying capacity through pasture and N cycling due to the return of plant material with better quality to the soil (lower C:N ratio).
As seen the importance of fertilizing pastures in all their types and regions where they are established, ILSA has nitrogen fertilizers obtained from the matrix as a tool. AZOGEL, rich in organic nitrogen and amino acids with a low C:N ratio, which allows the N present in the fertilizer to be absorbed by the plant. AZOSLOW is a pelletized organomineral fertilizer formulated from the combination of the AZOGEL matrix with mineral nitrogen sources, which promotes better use and absorption of N by plants, generating increases in forage productivity. In addition to favoring N absorption, the presence of the AZOGEL matrix contributes to the activity of soil microorganisms, enhancing the mineralization processes of nitrogen present in the soil organic matter. Nitrogen fertilization is essential for pasture establishment, tillering, quality and production (CORSI, 1994); however, applying N all at once can favor losses by leaching due to its mobility in the soil in the form of nitrate (NO3-). De Bortolli (2016) and Bernardon (2016) observed that nitrogen fertilization increased the availability of mineral N for plants in the surface layer of the soil, favoring pasture productivity. Nitrogen fertilization of pasture promotes greater biomass production and nutrient cycling, favoring the productivity of subsequent crops (SVERSUTTI, YADA, 2019).
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Authors
- Agr Eng. Dr. Angélica Schmitz Heinzen
- Agricultural Eng. Msc. Carolina Custodio Pinto
- Agricultural Eng. Msc. Thiago Stella de Freitas
