Response to the Letter to the Editor "The role of South American grazing lands in mitigating greenhouse gas emissions. A reply to: 'Reassessing the role of grazing lands in carbon-balance estimations: Meta-analysis and review' by ."

The health, environmental, and economic dimensions of future dietary transitions in Argentina

Diets link human health with environmental sustainability, offering promising pressure points to enhance the sustainability of food systems. We investigated the health, environmental, and economic dimensions of the current diet in Argentina and the possible effects of six dietary change scenarios on nutrient adequacy, dietary quality, food expenditure, and six environmental impact categories (i.e., GHG emissions, total land occupation, cropland use, fossil energy use, freshwater consumption, and the emission of eutrophying pollutants). Current dietary patterns are unhealthy, unsustainable, and relatively expensive, and all things being equal, an increase in income levels would not alter the health dimension, but increase environmental impacts by 33-38%, and costs by 38%. Compared to the prevailing diet, the six healthier diet alternatives could improve health with an expenditure between + 27% (National Dietary Guidelines) to -5% (vegan diet) of the current diet. These dietary changes could result in trade-offs between different environmental impacts. Plant-based diets showed the lowest overall environmental impact, with GHG emissions and land occupation reduced by up to 79% and 88%, respectively, without significant changes in cropland demand. However, fossil energy use and freshwater consumption could increase by up to 101% and 220%, respectively. The emission of eutrophying pollutants could increase by up to 54% for all healthy diet scenarios, except for the vegan one (18% decrease). We conclude that the health and environmental crisis that Argentina (and other developing countries) currently face could be mitigated by adopting healthy diets (particularly plant-based), bringing in the process benefits to both people and nature.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s11625-021-01087-7.

A paradigm shift to CO2 sequestration to manage global warming - With the emphasis on developing countries

Global land use changes that tend to satisfy the food needs of augmenting population is provoking agricultural soils to act as a carbon (C) source rather than sink. Agricultural management practices are crucial to offset the anthropogenic C emission; hence, Carbon sequestration (CS) in agriculture is a viable option for reversing this cycle, but it is based on hypotheses that must be questioned in order to contribute to the development of new agricultural techniques. This review summarizes a global perspective focusing on 5 developing countries (DC) (Bangladesh, Brazil, Argentina, Nigeria and Mexico) because of their importance on global C budget and on the agricultural sector as well as the impact produced by several global practices such as tillage, agroforestry systems, silvopasture, 4p1000 on CO₂ sequestration. We also discussed about global policies regarding CS and tools available to measure CS. We found that among all practices agroforestry deemed to be the most promising approach and conversion from pasture to agroforestry will be favorable to both farmers and in changing climate, (e.g., agroforestry systems can generate 725 Euro_eq C credit in EU) while some strategies (e.g. no-tillage) supposed to be less promising and over-hyped. In terms of conservative tillage (no-, reduced-, and minimal tillage systems), global and DC's land use increased. However, the impact of no-tillage is ambiguous since the beneficial impact is only limited to top soil (0-10 cm) as opposed to conventional mechanisms. Grasses, cereals and cover crops have higher potential of CS in their soils. While the 4p1000 initiative appears to be successful in certain areas, further research is needed to validate this possible mode of CS. Furthermore, for effective policy design and implementation to obtain more SOC stock, we strongly emphasize to include farmers globally as they are the one and only sustainable driver, hence, government and associated authorities should take initiatives (e.g., stimulus incentives, C credits) to form C market and promote C plantings. Otherwise, policy failure may occur. Moreover, to determine the true effect of these activities or regulations on CS, we must concurrently analyze SOC stock adjustments using models or direct measurements. Above all, SOC is the founding block of sustainable agriculture and inextricably linked with food security. Climate-smart managing of agriculture is very crucial for a massive SOC stock globally especially in DC's.

Are grassland soils of the pampas sequestering carbon?

A belief that grassland soils act as carbon sinks and mitigate greenhouse gas emissions generated by livestock production is common among some farming organizations. A recent theoretical analysis proposed that grazing lands in South America sequester carbon as soil organic matter but this result is controversial. Here, we search for empirical evidence of changes in the carbon stock in the grassland soils of the Pampean region of Argentina. For this purpose, 22 natural grassland sites were selected, distributed across the region. The sites were first sampled in 2007 as part of a regional survey of soil carbon stocks; they were re-sampled in 2019. The sites represent a wide range of soil and climate conditions. Samples were taken to a depth of 50 cm. Bulk density, and inorganic and organic carbon, were determined, and the carbon stocks were estimated on an equivalent mass basis. The results were analyzed using ANOVA. No statistically significant differences were found in either inorganic or organic carbon stocks between the sampling times. Across all the sites, the average organic carbon stock was 59.0 t ha^-1 in 2007 and 56.2 t ha^-1 in 2019. These results suggest that the Pampas grasslands are not sequestering carbon.