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Lal. Carbon Footprints 2026, 5, 10 Page 5 of 20

Soil C, the sum of SOC and soil inorganic carbon (SIC), is the heart of soil health. In turn, soil health is the
source of critical ESs, including food, energy, water, moderation of climate, etc. Thus, the strong
interconnectivity that depends on soil C dynamics is also called the Food-Energy-Water-Soil (FEWS) nexus.
Indeed, soil health (as moderated by its C content) is the most basic natural resource that is at the center of
the FEWS nexus. The FEWS nexus is moderated by the coupled cycling of carbon, water, and nutrients. This
coupling is sensitive to land use and management of soil and its disruption by anthropogenic activities. Such
disruption can lead to soil degradation, land desertification, and the creation of disservices because of
alterations in planetary processes. It is also this disruption that is the cause of the accelerated soil erosion,
water eutrophication, emission of GHGs, the drought-flood syndrome, and decline in food production along
with reduction in its nutritional quality and safety. Thus, soil C content must be maintained in the root zone
at an optimal level (1.5% to 2.5% by weight) for provisioning of ESs for humans and nature.

SOIL CARBON POOL AND GLOBAL WARMING
The terrestrial C pool has two components: (1) soil C and (2) the biomass C. Together, these two pools
contain ~2,870 Pg C, comprising 2,250 Pg of soil to 1 m depth and 620 Pg of biomass C. The soil C pool
comprises two components: SOC (1,500 Pg) and SIC (750 Pg). The soil C pool is ~78% (2,250 Pg C out of
2,870 Pg C) of the total terrestrial pool. The soil C pool can be a source or sink of atmospheric CO 2
depending on land use and management and other natural or anthropogenic factors. Thus, the aim of land
use and soil management is not only to decrease the source of GHGs but also to increase the C storage
capacity by re-carbonization of the terrestrial biosphere. Indeed, the interaction between soil and biotic pools
is affected by land use change, soil degradation, and drastic soil disturbance (deforestation, war and
explosives, plowing, irrigation and use of agro-chemicals).

The ACC may create positive feedback by aggravating an increase in the atmospheric C pool, and negative
feedback by creating new sinks of atmospheric CO . The ACC can increase global warming by accelerating
2
decomposition and altering the composition of SOM. However, credible and verifiable assessment of the
exact magnitude of increase in global warming is a major challenge. Thus, available information is highly
variable. For example, Ofiti et al. observed that 4.5 years of soil warming created divergent responses in
[13]
sub-soil (> 20 cm depth) compared to those in the surface soil. Melillo et al. reported that soil warming has
[14]
the potential to alter both pedologic (soil) and biotic (plant) processes which can affect C stock in the
terrestrial ecosystems (soil and vegetation). Melillo et al. also observed that soil warming increases losses
from soil C pool but increases C stock in woody tissue of trees, probably due to increase in N availability .
[14]
Global warming also leads to increase in soil respiration through its effect on autotrophic and heterotrophic
respiration. Schindlbacher et al. observed similar responses of soil warming to both types of respiration.
[15]
However, the autotrophic component had a distinct seasonal pattern and was the highest during summer.

SOIL MANAGEMENT PRACTICES WHICH SEQUESTER CARBON
Plow-based methods of seedbed preparation and indiscriminate use of agro-chemicals can aggravate
emissions from agro-ecosystems by degradation of soil and environment. Indeed, soil of agroecosystems can
be a source or sink of GHGs depending on land use and soil/crop/water management. When prone to
accelerated erosion and other degradation processes, soil is a source of GHGs. When the amount of C in
sediments is buried, it can be a sink. However, the net effect over the entire pathway (from upper reaches of
the watershed to the burial aquatic site) can make the erosion process a major but unknown source of GHGs.
Similarly, agro-inputs and farm operations are also a major source, especially plowing, use of nitrogenous
fertilizers, input of pesticides, grain drying, etc. Despite their importance in aggravating ACC, the precise or
credible magnitude of emissions from farm operations is not known. For example, an excessive use of
chemical fertilizers may aggravate soil degradation and increase GHG emissions. Wu et al. observed that
[16]