Fertilizing pasture with nitrogen and supplementing the cattle herd’s diet with selected nutrients can both reduce greenhouse gas emissions and raise yields and economic efficiency in pasture-based beef production systems.
This is the main finding of a study by researchers at São Paulo State University’s School of Agricultural and Veterinary Sciences (FCAV-UNESP) in Jaboticabal, in collaboration with colleagues at the University of Queensland in Australia, the University of Florida in the United States, the Southeast Livestock division of the Brazilian Agricultural Research Corporation – EMBRAPA, and the Alta Mogiana Regional Hub of the São Paulo State Agribusiness Technology Agency – APTA.
Preliminary results of the study, which was conducted as part of the Thematic Project “Management strategies to reduce environmental impacts of beef cattle production systems” supported by FAPESP, were presented during the annual project presentation meeting of the FAPESP Research Program on Global Climate Change (RPGCC).
“The aim of the project is to evaluate the effect of nitrogen fertilization and strategic diet supplementation on emissions of methane, nitrous oxide and carbon dioxide, pasture and animal yields, and economic efficiency in terms of gain per hectare and energy consumption,” said Ricardo Andrade Reis, a professor at FCAV-UNESP Jaboticabal and principal investigator for the project.
According to data from Brazil‘s Ministry of Agriculture, Livestock & Food Supply (MAPA), beef and dairy cattle account for 83.9% of the nation’s livestock (89% beef cattle, 11% dairy cattle). A large proportion of this herd consists of Zebu breeds raised mainly in extensive grazing systems, with the Nelore breed in the majority (80%).
Most cattle in Brazil are raised extensively, given the size of the territory and favorable climate. However, estimates suggest that approximately 80% of the 45-50 million hectares of pasture in the savannas of Central Brazil is degraded to some extent, owing largely to diminishing soil fertility resulting in sharply reduced capacity to support pasture and animal weight gain.
As a result, Brazilian beef cattle productivity has been low for decades, with pastures carrying approximately one animal per hectare and live weight gain in the range of 100 kg per hectare per year.
To mitigate the environmental impact of beef cattle production systems, increase productivity and stocking rates, and improve economic efficiency, in 2014, the researchers at FCAV-UNESP Jaboticabal began studying different tropical pasture management strategies using a technique known as light interception at 95%, with pasture height and fertilization as assessment criteria.
Light interception at 95% is based not on programmed rotational paddock grazing but on pasture height, continuously offering higher-quality forage with a higher leaf proportion in herbage, greater protein digestibility and soluble nitrogen, and low levels of nondigestible fiber, the main source of methane from ruminants, which they eliminate by belching and breathing out. Methane is the main greenhouse gas emitted by cattle.
In addition to the role of methane in climate change, its elimination through the animal’s mouth and nostrils represents a loss of between 2% and 12% of the gross energy from feed consumed, consequently affecting the animal’s performance in terms of meat production.
“We aim to regulate methane emissions and energy loss by forage management combined with diet supplementation to include more nutrients,” Reis said. “This will increase pasture stocking levels from one to three or four animals per hectare per year, for example, and free up more hectares for the rehabilitation of degraded pasturelands, which can be converted to forest.”
Fertilization and supplementation
Since 2014, the researchers have been conducting two experiments in a 60-hectare area belonging to FCAV-UNESP Jaboticabal.
In the first experiment, they are tracking the rise in Nelore bullock stocking rates in pasture consisting of palisade grass (Urochloa brizantha) managed to a height of 25 cm and fertilized with four levels of nitrogen – 0 kg, 90 kg, 180 kg and 270 kg per hectare for 150 days in the rainy season. They are also measuring emissions of methane, nitrous oxide and carbon dioxide in connection with these doses of nitrogen fertilizer.
In the second experiment, the researchers are feeding animals in this grazing regime a diet of salt and a protein supplement comprising soybean meal, urea, and corn distillery waste (CDG).
Preliminary results from the first experiment indicate that merely by supplying higher-quality forage (i.e., even without nitrogen fertilization) the stocking rate reached three head per hectare per year. Application of 180 kg of nitrogen during the rainy season boosted the rate to six head per hectare per year.
“We don’t yet know how long the non-fertilized pasture will support this animal load,” Reis said.
Enteric methane emissions due to nitrogen fertilization were lower than those for the cattle-raising industry without fertilization as reported by international bodies such as the Intergovernmental Panel on Climate Change (IPCC), regardless of the dose applied.
Weight gain varied from 980 g to 1.1 kg per day for pastures fertilized with nitrogen. “Weight gain under the current beef cattle grazing system varies from 500 g to 700 g per day,” Reis said.
Preliminary results from the second experiment also indicate that the protein/energy supplement results in an additional weight gain of 100 g-150 g per day compared with that obtained using mineral salt.
“This translates to a shorter finishing time and frees up pastureland earlier. Furthermore, methane emissions from the animals are reduced for a longer period of their lives,” Reis said.
Source : By Elton Alisson | Agência FAPESP