Greenhouse gas balance and carbon footprint of pasture-based beef cattle production systems in the tropical region (Atlantic Forest biome).

The production of beef cattle in the Atlantic Forest biome mostly takes place in pastoral production systems. There are millions of hectares covered with pastures in this biome, including degraded pasture (DP), and only small area of the original Atlantic Forest has been preserved in tropics, implying that actions must be taken by the livestock sector to improve sustainability. Intensification makes it possible to produce the same amount, or more beef, in a smaller area; however, the environmental impacts must be assessed. Regarding climate change, the C dynamics is essential to define which beef cattle systems are sustainable. The objectives of this study were to investigate the C balance (t CO2e./ha per year), the intensity of C emission (kg CO2e./kg BW or carcass) and the C footprint (t CO2e./ha per year) of pasture-based beef cattle production systems, inside the farm gate and considering the inputs. The results were used to calculate the number of trees to be planted in beef cattle production systems to mitigate greenhouse gas (GHG) emissions. The GHG emission and C balance, for 2 years, were calculated based on the global warming potential (GWP) of AR4 and GWP of AR5. Forty-eight steers were allotted to four grazing systems: DP, irrigated high stocking rate pasture (IHS), rainfed high stocking rate pasture (RHS) and rainfed medium stocking rate pasture (RMS). The rainfed systems (RHS and RMS) presented the lowest C footprints (-1.22 and 0.45 t CO2e./ha per year, respectively), with C credits to RMS when using the GWP of AR4. The IHS system showed less favorable results for C footprint (-15.71 t CO2e./ha per year), but results were better when emissions were expressed in relation to the annual BW gain (-10.21 kg CO2e./kg BW) because of its higher yield. Although the DP system had an intermediate result for C footprint (-6.23 t CO2e./ha per year), the result was the worst (-30.21 CO2e./kg BW) when the index was expressed in relation to the annual BW gain, because in addition to GHG emissions from the animals in the system there were also losses in the annual rate of C sequestration. Notably, the intensification in pasture management had a land-saving effect (3.63 ha for IHS, 1.90 for RHS and 1.19 for RMS), contributing to the preservation of the tropical forest.

Frequências de cortes em nove leguminosas forrageiras tropicais herbáceas cultivadas ao sol e sob plantação florestal / Cutting frequencies of nine herbaceous tropical forage legumes cultivated under full sun light and under a forest plantation

O objetivo deste trabalho foi estudar a produção e o valor nutritivo de nove espécies de leguminosas forrageiras herbáceas tropicais, cultivadas sob dois níveis de irradiação luminosa e seis frequências de corte na estação chuvosa, em Anhembi (SP), Brasil. Parcelas puras foram estabelecidas ao sol e sob plantação de Eucalyptus grandis, com 8 anos de idade, com 1.000 árvores/ha, que interceptou mais de 80% da radiação luminosa incidente. Avaliou-se a taxa de acúmulo de matéria seca, a proteína bruta e a digestibilidade in vitro da matéria seca em amostras de plantas colhidas em intervalos de 30, 60, 90 e 180 dias, com cortes adicionais aos 120 e 150 dias. Sob pleno sol, as leguminosas testadas toleraram cortes mais frequentes (intervalos de 30 - 90 dias), exceto o Lablab. Na sombra, o grau de tolerância variou conforme a espécie; em termos de produção de MS e de persistência, a Centrosema e a Puerária se destacaram dentre as demais leguminosas comparadas, quando os cortes foram realizados em intervalos de 60 dias, enquanto o Arachis e o Estilosantes foram os mais produtivos quando os cortes ocorreram em intervalos de 120 dias, mantendo o valor nutricional. O Alysicarpus e a Aeschynomene não persistiram sob o nível de sombreamento que prevaleceu nesse experimento.

The aim of this study was to evaluate the production and nutritive value of nine tropical legumes under two light intensities and six cutting regimens in the wet season, in Anhembi (SP) - Brazil. Pure stands were established in full light and under an eight-year-old eucalyptus plantation with 1.000 plants per hectare. The trees intercepted over80% of the incident radiation. Dry matter herbage accumulation, dry matter in vitro digestibility and crude protein under the cutting intervals 30, 60, 90 and 180 days, with additional cuttings at 120 and 150 days were evaluated. With the exception of Lablab, all other tested legume species tolerated higher cutting frequency under when grown under full sun light then under shade. The degree of shade-tolerance varied according to the species; Centrosema and Pueraria produced well at cutting intervals of 60 days, showing higher dry matter production and persistence while Arachis and Stylosanthes showed better results under longer cutting intervals, keeping the nutritional value, and can be indicated for differential grazing. Alysicarpus and Aeschynomene did not persist under the prevailing conditions.