Livestock farming systems on South American native grasslands: when production meets conservation

Resúmen

The livestock industry faces the double challenge of coping with the increasing demand for animal protein and reducing its high load on the environment. On the one hand, livestock has been recognized for its contribution to the economy, providing 40% of global agricultural GDP, ensuring a living for farmers, maintaining rural heritage and traditional farming landscapes, providing draft power, fuel, and sources of nutrients, particularly proteins. On the other hand, the livestock industry emits 13-18% of global greenhouse gas emissions, occupies 33% of total arable land and is responsible for 8% of global water use.

South American Río de la Plata grasslands comprise more than 500,000 km2, including all of Uruguay, north-eastern Argentina and southern Brazil. These grasslands provide feed for 43 million heads of cattle and 14 million sheep. The biome is habitat of 4000 native plant species, 300 species of birds, 29 species of mammals, 49 species of reptiles and 35 species of amphibians. They store 5% of the total soil organic carbon stock of Latin America on 3% of the area, and they protect soils from erosion. Cropping areas and livestock herds have shifted spatially. Regions that used to integrate crop-livestock systems have specialized in cropping, decreasing stocks but increasing beef confined systems (feedlots). Regions with historical predominance of cattle due to low-potential productive have been increasing in stocking rates which could aggravate overgrazing problems. Land-use change very likely increased provisioning services while very likely decreased supporting and regulating services. Overgrazing regimes with low forage allowances were predominantly associated with negative effects on provisioning and supporting and regulating ecosystem services. The most documented impacts of land use-change and overgrazing include: reducing soil organic carbon stocks and the diversity of plants, birds and mammals, and increasing soil erosion.

In order to identify the diversity in farming systems, the first biome-wide beef farm typology of the Rio de la Plata grasslands was constructed. While seven farm types were identified, most of the farms belonged to the family farms, with cow-calf operations using native grasslands. We identified positive deviant farms, which performed excellently in economic and environmental terms when compared to the other farms in the region, and, more generally, to farms from OECD countries. These positive deviant farmers achieved 192 kg LW ha-1 yr-1 or 201 US$ ha-1 year-1 with negligible fossil energy consumption and phosphorus surplus, low carbon footprint (13 kg CO2 eq kg LW-1) and having over 95% of their land under native grassland. This means that the native grassland-based farming systems of the Río de la Plata grasslands region have the potential to produce high-quality beef with low use of inputs and preserve biodiversity, thus constituting one of the most sustainable livestock farming system models. However, the greenhouse gas emissions per unit of product may be high when compared to other forms of protein production as a consequence of the digestive system of the ruminant.

Droughts may affect grazing systems at multiple levels: they reduce plant growth and biomass production, decrease intake, weight, and reproductive performance of livestock, increase costs and reduce income for farmers, and affect rural communities and even countries’ economies. The relationship between management and resilience to drought at paddock and farm level was studied. At paddock level, higher herbage allowance increased the resistance of herbage accumulation rate and animal weight. A positive relationship was found between pre-drought herbage height and resistance of herbage accumulation to drought, which means that herbage height can be used as a guideline for grassland management. The sheep to cow ratio was negatively correlated with pregnancy rate of cows, a key variable defining meat production and farm income.

The economic and environmental issues with livestock production systems discussed above demand local actions by stakeholders. One such action is to actively work on the redesign of individual farms, to improve farmer livelihoods and ecosystem service provision. To aid this process we present and evaluate a dynamic whole-farm simulation model (PASpALuM). The model elucidates the relations between grazing management, productivity and environmental impact. The herbage dynamics module was evaluated against experimental data, showing acceptable simulation of the seasonal dynamics of herbage height and mass. A simulation exercise explored the effect of grazing management on enteric methane emissions and soil organic carbon from 2007 to 2009.

Maintaining this example of nature inclusive agriculture and improving it to the level of agriculture-inclusive nature, seems possible by changing grassland management strategies. Contributions to greenhouse gas emissions by livestock will remain, but this should be seen as the price to be paid for maintaining a unique and priceless biome that cannot be maintained in another way than through low-intensity grazing by ruminants. The contribution of greenhouse gas emissions from livestock systems on native grasslands is determined by the carrying capacity of the grasslands and will remain much lower per hectare than that of intensive pastures. Solutions for global meat production should be considered within social and ecological boundaries. Such quest is not advanced by unilateral reliance on one size fits all efficiency measures.