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Zhang et al. Carbon Footprints 2025, 4, 36 https://dx.doi.org/10.20517/cf.2025.29 Page 5 of 17

cooking and heating, thereby closing a key nutrient and energy loop within the farm system. Thus, this
manure is not returned to the grassland. At the same time, the farmers ride motorcycles instead of riding
horses to manage the herd and consume power for living and lighting. Therefore, the energy consumption
that is directly or indirectly generated can contribute to the GHG emissions, which act as farm input and
influence the GHG balance of the yak grazing farm systems on the QTP.

GHG emission inventory data and calculation methods
The partial life-cycle-assessment method that was evaluated followed the whole-system GHG balance in
[25]
compliance with International Organization for Standardization (ISO, 2006) protocols, with the findings
contextualized by both land area and annual LWG. The data underpinning this analysis were synthesized
from multiple sources. Primary data included field-level quantifications of carbon sequestration and
CH /N O fluxes from local yak grazing operations, a subset of which was acquired from the aforementioned
4
2
experiments . Complementing this, secondary data on CH and N O emissions from various sources -
[26]
2
4
namely the field, night pens, manure heaps, and excrement (dung and urine) patches - were sourced from
the existing literature, specifically the work of Sun et al. . The CH emission factor from yak enteric
[23]
4
[24]
fermentation was adopted from Yang et al. . Our assessment of GHG emissions, grounded in the Inter-
Governmental Panel on Climate Change (IPCC, 2006) framework, focused on those linked to the supply
[27]
chain and on-farm use of inputs, with input quantities being sourced from local farm data. The system
boundary for this analysis was defined to omit emissions from two key areas: biological processes (i.e.,
breeding and calving) and the embodied emissions in infrastructure, buildings, and vehicles (including their
construction, maintenance, and operation). Thus, the GHG emission inventory in this system included
pasture soil carbon, CH and N O emission/uptake, enteric CH emission, CH and N O emission from
2
4
4
4
2
manure management and indirect GHG emission from farm input [Table 2]. Furthermore, we calculated
the total GHG emission by summing the individual emission sources. The details of the inventory and
calculation methods are described below.
Carbon sequestration
Carbon sequestration was quantified by following the methodology of Sun et al. (2012) . This approach
[23]
involved tracking changes in the organic carbon stock of the topsoil (0-5 cm). To this end, undisturbed soil
core samples were obtained from the Ah-horizon annually from 2011 through 2013 for analysis. Soil
samples were collected from the different grazing farm sites and the fenced site with a stainless steel
cylinder. Soil organic carbon (SOC) was determined using the wet combustion method with K Cr O and
7
2
2
concentrated H SO at 170-180 °C. Bulk density (BD) was measured by dividing the mass of the samples
2
4
that were oven-dried at 105 °C to constant weight by the core volume. SOC sequestration (SOCS) was
[23]
calculated using
SOCS = SOC × BD × (1 - RF) × D
To determine the net CO fluxes to the atmosphere, we analyzed changes in carbon sequestration over the
2
2012-2013 period. This net flux represents the overall balance of carbon, accounting for inputs via
autotrophic fixation and outputs through autotrophic respiration (from plant metabolism) and
heterotrophic oxidation (from organic matter decomposition). The calculation of carbon sequestration was
based on several key variables: SOC storage (SOCS, kg m ), which was computed using the SOC
-2
concentration (SOC, mg g ), BD (g cm ), the volumetric fraction of rock fragments > 2 mm (RF), and the
-3
-1
sampling depth (cm). The annual rate of SOCS [ASOCS, kilograms per hectare per year (kg ha year )] was
-1
-1
then determined by dividing the change in SOCS from 2011 to 2013 by the number of years. It should be
noted that potential losses of carbon and nitrogen through leaching were not considered within the scope of
this study.