N-fertilization of tropical pastures improves performance but not methane emission of Nellore growing bulls.

Grazing management and N-fertilizer have been reported to improve tropical forage productivity and quality, however, their effect on methane emission of grazing animals remains uncertain. Therefore, this study aimed to assess the effects of increasing application rates of nitrogen (N) fertilization of Marandu palisadegrass under continuous stocking on intake, digestibility, nitrogen balance, and enteric methane emissions of Nellore growing bulls. We hypothesized that changes in the forage nutritive value caused by N fertilization of pastures combined with adequate grazing management (e.g., greater crude protein [CP] and digestibility) would lead to an increase in animal productivity (e.g., greater average daily gain [ADG] and gain per area), and then, to a decrease in methane emission intensity. Treatments consisted of different annual application rates of nitrogen fertilization: 0, 75, and 150 kg N/ha using ammonium nitrate (32% N) as the nitrogen source. The experimental design was completely randomized, with three treatments and four replications (12 paddocks). Intake, digestibility, N balance, and methane emissions were measured in eight animals per treatment. CP intake, digestibility and N balance increased linearly with the increase in N fertilization (P < 0.05). In addition, stocking rate (SR) and ADG linearly increased from 1.75 animal unit (AU = 450 kg)/ha and 0.62 kg/d (0 kg N/ha) to 3.75 AU/ha and 0.82 kg/d (150 kg N/ha), respectively. Individual methane emissions nor methane emission intensity were affected by treatment with an average of 164.7 g/d and 199.7 g/kg ADG (P > 0.05). Annual N fertilization with ammonium nitrate between 75 and 150 kg N/ha in palisadegrass pastures under continuous stocking enhances animal performance per unit area yet not affecting neither methane production nor intensity.

The availability of nitrogen in the soil is one of the main factors that can affect plant growth and characteristics. Nitrogen fertilization is a tool to increase the efficiency in the productive responses of grazing beef cattle, reconciling the greater production per area, reduction of the production cycle, maximization of the use of nutrients, with the maintenance of the system sustainability by enhancing animal production indexes. The present study evaluated performance and methane production of Nellore growing bulls grazing continuously stocked Marandu palisadegrass fertilized with three rates of ammonium nitrate (0, 75, and 150 kg N/ha). Although nitrogen fertilization did not affect individual methane production, both stocking rate and average daily gain linearly increased as fertilization rate increased, thus increasing the beef productivity.

Response of Pasture Nitrogen Fertilization on Greenhouse Gas Emission and Net Protein Contribution of Nellore Young Bulls.

This study aimed to evaluate the greenhouse gas (GHG) emission and net protein contribution (NPC) of Nellore young bulls grazing marandu palisade grass (Urochloa brizantha cv. Marandu) under three levels of pasture nitrogen (N) fertilization during backgrounding and finished on pasture or feedlot, based on concepts of sustainable intensification. The treatments were: System 1: pastures without N fertilizer during backgrounding, and animals finished on pasture supplemented with high concentrate at a rate of (20 g of concentrate per kg of body weight; P0N + PS); System 2: pastures fertilized with 75 kg N ha−1 year−1 during backgrounding and animals finished on feedlot fed a total mixed ration (TMR; P75N + F); and System 3: pastures fertilized with 150 kg N ha−1 year−1 during backgrounding, and animals finished on feedlot fed a TMR (P150N + F). During backgrounding, all pastures were managed under a continuous and put-and-take stock grazing system. All animals were supplemented with only human-inedible feed. Primary data from systems 1, 2 and 3, respectively, in the field experiment were used to model GHG emissions and NPC (a feed-food competitiveness index), considering the backgrounding and finishing phases of the beef cattle production system. Average daily gain (ADG) was 33% greater for the N fertilizer pastures, while carcass production and stocking rate (SR) more than doubled (P75N + F and P150N + F). Otherwise, the lowest GHG emission intensity (kg CO2e kg carcass−1) was from the P0N + PS system (without N fertilizer) but did not differ from the P75N + F system (p > 0.05; pastures with 75 kg N ha−1). The main source of GHG emission in all production systems was from enteric methane. Moreover, NPC was above 1 for all production systems, indicating that intensified systems contributed positively to supply human protein requirements. Moderate N fertilization of pastures increased the SR twofold without increasing greenhouse gas emissions intensity. Furthermore, tropical beef production systems are net contributors to the human protein supply without competing for food, playing a pivotal role in the food security agenda.

Pasture management and greenhouse gases emissions

Pastures are important environments worldwide because they offer many ecosystem services and sustain meat and milk production. However, pastures ecosystems are responsible for greenhouse gas (GHG) emission. The major GHGs include CO2, CH4, and N2O. The present review summarizes GHG emission from pasture ecosystems and discusses strategies to mitigate this problem. In pastures, emissions originate from animal excretion, fertilization, and organic matter decomposition. Emissions of specific gases can be measured based on certain factors that were recently updated by the United Nation's Intergovernmental Panel on Climate Change in 2019. Urine is the main source of N2O emission. Forage structure is an important factor driving GHG transport. Forage fiber content and animal intake are the key drivers of enteric CH4 emission, and the introduction of forage legumes in pasture systems is one of the most promising strategy to mitigate GHG emission.

Performance and feed intake of beef heifers on rotational grazing of natural grassland receiving protein and energy supplement in cool season / Desempenho de bezerras de corte em pastoreio rotativo em pastagem natural recebendo suplemento proteico-energético

ABSTRACT: The aim of this study was to evaluate the performance and feed intake of grazing beef heifers on two grazing intervals determined by thermal sum related to leaf elongation duration during cool season on natural grasslands. A complete randomized block design experiment with two treatments and three replications was conducted from May to September 2011 in the central part of the state of Rio Grande do Sul, Brazil. The treatments were two thermal sums calculated at 375 and 750 degrees-days (DD) to determine the intervals between grazing periods in a rotational grazing system. Thirty six beef heifers with average age of 18 months old and (initial body weight = 220±14kg) were used, all heifers received ground corn supplement at a rate of 5g kg-1 of body weight per day, at 2p.m., throughout the experiment and had free access to mineral and protein supplementation (450g kg-1 of CP). Similar average daily gain (ADG), beef production gain (BPG) and feed intake (FI), were obtained in both treatments. Leaf elongation duration is an alternative grazing management tool for improved animal production and to increase animal stocking rate.

RESUMO: Objetivou-se avaliar o desempenho e consumo de matéria seca de bezerras manejadas em pastoreio rotativo, com intervalos de pastoreio definidos por duas somas térmicas relacionadas à duração de elongação foliar de dois grupos funcionais de gramíneas durante a estação fria em pastagem natural. O delineamento experimental foi o de blocos completamente casualizados, com dois tratamentos e três repetições de área na região central do Rio Grande do Sul, Brasil. Os tratamentos foram duas somas térmicas: 375 e 750 graus-dias (GD), que determinaram os intervalos entre os pastoreios. Foram utilizadas trinta e seis bezerras de corte com idade média de 18 meses e peso corporal médio de 220±14kg. Durante todo o experimento, as bezerras receberam como suplemento grão de milho moído a uma taxa de 0,5% do peso corporal por dia, às 14:00 horas e tiveram livre acesso à suplementação proteínada (45% PB). Não houve diferença para o ganho médio diário, ganho de peso por área e consumo de matéria seca entre os tratamentos. A soma térmica como intervalo de descanso entre os pastoreios mostrou-se uma alternativa de manejo para aumentar a taxa de lotação.