The establishment of sustainable soil waste management practices implies minimizing their environmental losses associated with climate change (greenhouse gases: GHGs) and ecosystems acidification (ammonia: NH₃). Although a number of management strategies for solid waste management have been investigated to quantify nitrogen (N) and carbon (C) losses in relation to varied environmental and operational conditions, their overall effect is still uncertain. In this context, we have analyzed the current scientific information through a systematic review. We quantified the response of GHG emissions, NH₃ emissions, and total N losses to different solid waste management strategies (conventional solid storage, turned composting, forced aerated composting, covering, compaction, addition/substitution of bulking agents and the use of additives). Our study is based on a meta‐analysis of 50 research articles involving 304 observations. Our results indicated that improving the structure of the pile (waste or manure heap) via addition or substitution of certain bulking agents significantly reduced nitrous oxide (N₂O) and methane (CH₄) emissions by 53% and 71%, respectively. Turned composting systems, unlike forced aerated composted systems, showed potential for reducing GHGs (N₂O: 50% and CH₄: 71%). Bulking agents and both composting systems involved a certain degree of pollution swapping as they significantly promoted NH₃ emissions by 35%, 54%, and 121% for bulking agents, turned and forced aerated composting, respectively. Strategies based on the restriction of O₂ supply, such as covering or compaction, did not show significant effects on reducing GHGs but substantially decreased NH₃ emissions by 61% and 54% for covering and compaction, respectively. The use of specific additives significantly reduced NH₃ losses by 69%. Our meta‐analysis suggested that there is enough evidence to refine future Intergovernmental Panel on Climate Change (IPCC) methodologies from solid waste, especially for solid waste composting practices. More holistic and integrated approaches are therefore required to develop more sustainable solid waste management systems.

Goat milk production is an important agricultural resource in the Mediterranean basin. Market demands and scarcity of pastures during drought periods has led to farms becoming more intensive and based on imported concentrate feeds. The use of alternative feedstuffs from agro-industry can help decrease dependence on external concentrates, while preventing the environmental issues associated with livestock production and by-product disposal. From a life-cycle assessment perspective, we investigated the change on greenhouse-gas (GHG) emissions of replacing a conventional dairy goat diet in southern Spain with two alternative dietary strategies, including tomato waste or olive by-products silages. The effect on enteric methane emissions and milk productivity was assessed through specific feeding trials. Experimental data were integrated within a modelling framework comprising different submodels to describe the farm system and associated production chain. A new model describing carbon and nitrogen losses from solid waste was applied to estimate the emissions associated with the baseline scenarios for food by-product management. The assessment revealed that the two dietary strategies achieve GHG reductions (~12–19% per kg milk). In both cases, nitrous oxide and carbon dioxide emissions from crop production were partially reduced through the displacement of typical concentrate ingredients. An additional mitigation effect was obtained when including tomato wastes in the diet because it reduced the methane emissions from enteric fermentation. Results suggested that use of agro-industrial residues for feeding is a feasible mitigation option in this case. However, as organic by-products could have alternative uses (bioenergy, soil amendment), with different implications for land use and soil carbon stocks, a more complete overview of both scenarios is recommended. Potential trade-offs from non-GHG categories may play an important role in a decision-making process.

Purpose: Transhumance has rarely been analyzed through LCA approaches, and there is little evidence about its emissions level when conducted under different practices (by truck or on foot) or compared to sedentary livestock systems. Moreover, mobile pastoralism is strongly linked to natural resources by its seasonal grazing patterns, thereby occupying the niche of wild herbivores. Considering natural emission baselines in these ecosystems could have relevant effects when estimating their carbon footprint. Materials and methods: Inventory data of 20 sheep farms was collected to estimate the carbon footprint (CF) of lamb meat produced. Farms were divided into three sub-groups representing typical management practices in the region: (1) sedentary (SED), (2) transhumance by truck (THT), and (3) transhumance on foot (THF). Livestock GHG emissions were modeled according to herd structure and IPCC guidelines. Off-farm emissions from external feeds and fuels were accounted based on existent LCA databases. A natural baseline of wild herbivores was established from the population of red deer reported in a hunting preserve, previously considered to be a reference for the natural carrying capacity in Mediterranean ecosystems. GHG emissions of wild herbivores were estimated through two methods based on (1) IPCC guidelines and (2) allometric regression equations. Results and discussion: Carbon footprint ranged from 16.5 up to 26.9 kgCO₂-eq/kg of lamb liveweight (LW). Significant differences were identified among sedentary and transhumant farms, the latter consistently showing lower CF values (SED: 25.1 kg CO₂-eq/kg LW, THT: 18.3 kg CO₂-eq/kg LW, THF: 18.2 kg CO₂-eq/kg LW). Sedentary farms resulted in higher GHG emissions (+ 27%) and higher CO₂ and N₂O, contributions derived from the consumption of additional feeds. Both methods applied to compute emissions for wild herbivores led to similar results (25.3–26.8 Mg CO₂-eq/km²), comparatively lower than estimation for transhumant sheep (47.7 Mg CO₂-eq/km²). When considering natural baseline emissions, the CF of transhumant lamb meat is reduced by almost 30%, reaching values quite below those reported for intensive lamb production systems in Spain. Conclusions: From our results, mobility of grazing livestock can be considered as a strategy promoting climate change mitigation. This is achieved mainly by reducing the need of external feeds, while maximizing the use of local forage resources that otherwise would be difficult to valorize. Further reductions in the CF result when considering natural baseline emissions. The application of this new GHG accounting perspective could have relevant implications when aiming at climate neutrality of grazing-based ruminant systems.

Pastoralism in Old World savannas is known to emit a significant share of global livestock-sourced greenhouse gases (GHG). Here, we compare calculated emissions from animals in a wildlife-dominated savanna (14.3 Mg km⁻²), to those in an adjacent land with similar ecological characteristics but under pastoralism (12.8 Mg km⁻²). The similar estimates for both, wildlife and pastoralism (76.2 vs 76.5 Mg CO₂-eq km⁻²), point out an intrinsic association of emissions with herbivore ecological niches. Considering natural baseline or natural background emissions in grazing systems has important implications in the analysis of global food systems.