Abstract
Animal production systems are increasingly required to co-produce meat products and other ecosystem services. Sown biodiverse pastures (SBP) were developed in Portugal as an improvement over semi-natural pastures (SNP). SBP increase yields and animal intake during grazing, are substantial carbon sinks, and the abundance of legumes in the mixtures provides plants with a biological source of nitrogen. However, the data available and the data demands of most models make integrated modelling of these effects difficult. Here, we developed “BalSim”, a mass balance approach for the estimation of carbon and nitrogen flows and the direct greenhouse gas (GHG) balance of the two production systems. Results show that, on average, the on-farm GHG balance is −2.6 and 0.8 t CO2e/ha.yr for SBP and SNP, respectively. Ignoring the effects of carbon sequestration, and taking into account only non-CO2 emissions, the systems are responsible for 17.0 and 16.3 kg CO2e/kg live weight.yr. The annual analysis showed that non-CO2 emissions were highest in a drought year due to decreased yield and stocking rate. We also showed through scenario analysis that matching the grazing level to the yield is crucial to minimize emissions and ensure reduced feed supplementation while maintaining high soil carbon stocks.
Highlights
The idea that current global production patterns of animal products, meat, in particular, are unsustainable gained popular support and media attention following the 2008 “Livestock’s Long Shadow” report [1]
In this paper we propose a mass balance approach based on the OECD model, but tailor-made for this application at the level of detail that fits the limited available data on Sown biodiverse pastures (SBP)
We considered that each livestock unit (LU) can be partitioned between one adult cow (1 LU/head) and a corresponding less than one-year old weaner calf (0.4 LU/head)
Summary
The idea that current global production patterns of animal products, meat, in particular, are unsustainable gained popular support and media attention following the 2008 “Livestock’s Long Shadow” report [1]. Dominant global animal production systems must change to cope with future demand sustainably, and there is room for improvement. Extensive grass or grass/legume-based systems use marginal land for grazing [5], accelerate nutrient recycling [6], and can sequester carbon (C) in soils [7]. SBP are self-reseeding grass-legume pastures with up to 20 native and high-yielding species/cultivars with an annual life cycle. They increase grassland productivity and sustainable stocking rates [7]. SBP occupy more than 4% of the country’s agricultural land [8,10] They can be a prime example of how to improve the sustainability of meat production systems
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