Sustainable intensification of agriculture andlivestock production in Brazil: a meta-analysis of soil C changes in integrated systems

The use of agroforestry systems and integrated production models have been considered as viable options for tropical regions. Several studies have reported that these sustainable production systems have decreased the GHG emissions into the atmosphere and increased soil carbon stocks. If successful, the integration of crops, forests, and livestock will account for around 23% of Brazil’s 112 million ha of pasture. Every ha of integrated agriculture and livestock farming (IALF) pasture has the potential to remove an average of 3.79 tCO2e from the atmosphere per year. However, given the dynamics and complexity of soil management required when integrating different production components, it is necessary to perform regionalized research about soil carbon storage capacity. According to the Fourth National Communication of Brazil to the United Nations Framework Convention on Climate Change (UNFCCC), greenhouse gas (GHG) emissions in Brazil totaled 1,467 teragrams (Tg) of CO2e in 2016. In the search for more sustainable agricultural systems that increase the productivity of cultivated areas and at the same time can mitigate GHG emissions, the National Plan for Low Carbon Emission in Agriculture (ABC Plan), now renamed ABC+, was created aiming to incorporate new practices to mitigate GHG emissions for the 2020–2030 period. The objective of ABC Plan is to expand the agricultural land using the technologies outlined in the plan by 72 million ha - the area is currently close to 50 million ha - and achieve an estimated mitigation capacity of 1.1 billion tCO2e by 2030. Areas that integrate agriculture, livestock and forests, known as agrosilvopastoral systems are projected to expand by over 10 million ha in the period, according to ABC+ Plan.  In order to make recommendations about the adoption of agrosilvopastoral systems, the objective of this study was to summarize the data from literature using the meta-analysis to evaluate the effect of integrated production systems introduction on soil carbon stocks, considering the different biomes in Brazil. When we compared the land use with low-productivity pastures and integrated production systems, we found an increase in soil C stocks under agropastoral, silvopastoral and agrosilvopastoral systems. Considering all the evaluated Brazilian biomes, higher soil C stocks were found for the integrated production systems when compared to low-productivity pastures. The Cerrado and Atlantic Forest biomes showed a higher sampling value, and this is due to the fact that  integrated production systems are more adopted in these two Brazilian biomes. Additionally, the agrosilvopastoral systems in the Cerrado biome showed the highest soil C stocks, but did not differ in relation to the Atlantic Forest and Pampa biomes. The agrosilvopastoral and silvopastoral systems were efficient on soil C inputs, and the values were 65.58 and 57.14%, respectively, higher than in low productivity pasture at 0-30 cm depth. These findings indicate that the land use with pastures and the introduction of trees in productive systems can reverse soil carbon losses. Additionaly, the introduction of trees can increase soil carbon stocks, supporting the potential of agroforestry systems to recover low-productivity areas in Brazil.