Pasture fertilization in soils in the center-west and south of Brazil

Currently, the pasture area occupies around 159 million hectares, around 18,5% of the national territory. According to the Brazilian Association of Meat Exporting Industries – Abiec, Brazil is the second largest producer and largest exporter of beef. When we analyze production systems, we find that around 87% of all beef produced in the country is grass-fed (Embrapa, 2020). This provides high competitiveness due to lower production costs.

When we analyze milk production in Brazil, despite the high modernization of the production system, ceasing to be based on pastures and migrating to confined and semi-confined systems, pasture still finds itself as a food of great importance for the production system, being it under grazing or even in the form of pre-dried hay and silage, providing an excellent source of fiber for dairy cows.

For this reason, the quality of pastures is strategically important for the producer, with a direct relationship with the health and increased productivity of the herd, whether beef or dairy.

Among the species cultivated in the Center-West and South regions of the country, some have high genetic potential for forage production, especially when their soil fertility requirements are met. The problem is that a large part of the soil covered with pasture has low fertility and does not meet the demand for macro and micronutrients essential for the good development of the cultivar, limiting its productivity and consequently the conversion into animal products.

Therefore, to avoid nutrient deficiency and degradation, fertilization is a necessary management strategy to keep the production system healthy and economically viable.

When we talk about pasture fertilization, we cannot leave aside the need to correct acidic soils, as this will directly impact the use of nutrients by forage plants. Soil analysis is a fundamental tool for identifying the need and type of limestone to increase base saturation and reduce soil acidity by neutralizing aluminum, which is toxic to plants, providing conditions for greater nutrient availability.     

In certain situations, the use of agricultural gypsum after the use of limestone is also necessary, in order to correct the deeper layers of the soil (20 to 40 cm), meeting the needs for calcium and sulfur. This management, when necessary, provides conditions for the plant to develop its root system, reaching deeper layers in the search for water and nutrients.     

The southern region of Brazil is characterized by a predominantly subtropical climate, with well-defined seasons and large temperature variations. It is the coldest region in the country, with frosts occurring during the winter. For this reason, the forage species adopted differ slightly from other regions of the country.

The most used forage crops in this region are: alfalfa, oats, ryegrass, elephant grass cultivars, sudan grass, millet, forage sorghum, clover cultivars, cultivars of the genus Cynodon (Tifton, costcross, etc.), in addition to native fields in the southern region of Rio Grande do Sul.

The Brazilian Central-West region is characterized by a semi-humid tropical climate, with two well-defined seasons. The summer is hot and humid, with a high volume of rain and a dry winter. Being a region where there is a predominance of grasses of the genus brachiaria such as marandu, xaraés, piatã and the genus Panicun such as tanzânia and Mombaça.

The forages mentioned above differ in terms of their nutritional requirements, with some being more demanding compared to others. For this reason, whenever the livestock farmer decides to implement a new cultivar on his property, it is extremely important to take into account the predominant climate of the region, the soil and relief characteristics, the management that best suits the production system, the degree of dry matter productivity per desired hectare and the level of investment to achieve this productivity. In this regard, we must take into account the fertility level of the forage plant chosen during implementation and during maintenance, and take care of it to obtain greater efficiency.

When we talk about fertilizing forage plants, the main nutrient is phosphorus, which provides better plant establishment, root development and tillering. The greater the tillering, the greater the forage production and animal stocking rate. This type of response was observed in Mombasa by Carneiro et al. (2017) who evaluated different sources and doses of phosphorus and concluded that fertilization promoted greater tillering, plant height and greater dry mass production. Costa et al. (2017) also observed this response pattern in Massai grass.

Another important nutrient for both the implementation and maintenance of forage plants is potassium. The extraction levels of this nutrient in pastures are high, around 2% in the dry matter of the harvested forage (Oliveira, 2008). However, in grazing systems, there is a return to the system via recycling through losses during the grazing process and the deposition of feces and urine. Even so, soil correction at the time of implementation and during maintenance is necessary, since potassium deficiency can cause a decline in the growth and development of both the aerial part and root system of plants.

Nitrogen, in turn, is an extremely important fertilizer for pasture-based animal production systems, being responsible for significant increases in dry mass production, which allows increases in the stocking rate and animal gain per area. Furthermore, the combination of nitrogen fertilization with sulfur is well documented in the literature and brings significant gains in productivity and bromatological quality for forage crops.

Santos et al. (2006), evaluated the bioeconomic efficiency of pasture fertilization in southern Brazil and found that investment in fertilization of natural pastures is biologically and economically viable in doses of up to 200 kg of N/ha, with an increase in live weight production, margin and efficiency in converting N into animal products.

Canto et al. (2009) evaluated the production of rearing beef cattle under continuous stocking in Tanzania grass pastures fertilized with increasing doses of nitrogen (100, 200, 300 and 400 kg/ha). The authors' response was a significant increase in forage production, which allowed an increase in the stocking rate from 3,2 AU/ha at a dose of 100 kg of N/ha to 7,1 AU/ha at a dose of 400 kg. of N/ha, with an average daily gain of 730 g animal/day. For doses of 200 and 300 kg of N/ha, the increase in stocking rate was 4,5 and 5,8 AU/ha, respectively. With the increase in stocking rate obtained, the authors also found greater animal production per unit area. These results make clear the potential of using nitrogen fertilizers.

It is worth remembering that, whenever we intensify the level of fertilization in forage plants, it is necessary to increase the harvesting efficiency of this material through grazing management. With more frequent grazing, with a shorter interval between grazing for rotational systems and adjustment in the stocking rate to make better use of the forage produced in the case of continuous systems. This ensures that all forage produced is harvested at the optimum point, combining the production of green leaves and the nutritional value of the forage.

Bibliography consulted

CARNEIRO, JSS; SILVA, PSS; SANTOS, ACM; FREITAS, GA; SILVA, RR Response of grass mombasa under the effect of sources and doses of phosphorus in the fertilization formation. Journal of Bioenergy and Food Science, v.4, n.1, p.12- 25, 2017.

COSTA, NL; JANK, L.; MAGALHÃES, JA; GIANLUPPI, V.; FOGAÇA, FHS; RODRIGUES, BHN; SANTOS, FJS Morphogenetic characteristics and forage accumulation of Megathyrsus maximus x M. infestum cv. Massai in response to phosphate fertilizer. Proceedings... XII Northeastern Congress of Animal Production.

OLIVEIRA, PPA; PENATI, MA; CORSI, M. Soil correction and pasture fertilization in intensive dairy production systems. EMBRAPA, 2008.

SANTOS, MER & FONSECA, DM Pasture fertilization in animal production systems. Ed. UFV, Viçosa, 2016.

*Per Eliana Geremia (in the picture), livestock specialist at Mosaic Fertilizers.