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Salmerón et al. Carbon Footprints 2026, 5, 17 Page 19 of 26

agro-industrial residues beyond those from the olive oil industry, given the wide diversity of biomass
available in Andalusia .
[86]
This study considered a uniform biochar application rate of 5 t ha across the study region. However,
-1
alternative application rates are possible, and they would likely influence both soil responses and the total
land area treated [11,69] . For instance, severely degraded sites may require higher or more frequent applications
to effectively contrast degradation processes [62,87] . While the chosen application rate determines the carbon
sequestered per hectare, the estimated regional carbon capture remains unchanged as biochar production is
constrained by biomass availability. Consequently, varying the dosage redistributes the same total quantity of
sequestered carbon across a different spatial extent rather than altering the total mitigation potential.

Beyond application rates, biochar’s agronomic benefits (i.e., erosion reduction, lower fertilizer and water use,
and yield increase) are subject to local variability due to soil heterogeneity. However, regional modeling
studies suggest that local fluctuations tend to offset across space, making aggregated impact factors a robust
proxy for estimating overall trends [52,66,69] . While the absolute magnitude of these benefits may vary by site, the
direction of environmental impacts remains consistent, allowing regional data to capture broad spatial
patterns effectively [66,69] . For these reasons, results in this study are presented at an aggregated regional scale,
for which the use of regionally averaged factors provides a robust representation of overall trends, as local
heterogeneity in soils, climate, and management tends to offset. By contrast, analyses conducted at higher
spatial resolution or focused on a limited subset of locations (e.g., individual farms or specific grid cells)
cannot rely on regional averages and require context-specific empirical data to generate reliable estimates.
Future research should therefore prioritize the development of high-resolution databases on
biochar/AVS-induced soil effects to support site-specific assessments and enable more targeted and optimal
deployment of these strategies.

AVS deployment in this study was limited to irrigated olive groves with low slopes (< 5%), a constraint that
helps mitigate concerns related to grid access and technological feasibility [30,32] . However, future analyses
could expand this boundary, as some commercial AVS providers report feasibility on slopes up to 30% . A
[88]
more critical challenge lies in the grid’s ability to absorb the high deployment potential of renewables (up to
52 TWh) and address potential grid instability arising from the intermittent nature of solar power.
Consequently, the investment in grid reinforcement and energy storage strategies is essential to enhance
system resilience, reduce stress, and minimize reliance on fossil-based peak generation [49,89] . These challenges
have been underscored by events such as the 2025 national blackout . Alternative solutions for utilizing
[90]
surplus on-site electricity generation can also be explored, such as producing hydrogen, which can be stored
for use during periods of low renewable energy availability or exported to support the growing demands of a
future hydrogen economy.

Regarding the interactions between photovoltaic panels and the agroecosystem, our analysis assumed no
negative impact on crop yield. This assumption is grounded in the use of a dual-axis tracking system, which
has been shown to minimize shading effects , distinguishing it from static designs that have reported yield
[33]
reductions of up to 10% . Beyond yield preservation and the modeled water savings, future research should
[32]
quantify additional ecosystem services. For instance, AVS-induced groundcover and cooler
microclimates [34,59] could not only complement the erosion reduction effects of biochar in olive groves, but
also offer opportunities to establish biodiversity corridors in the unfarmed strips of land created, thereby
enhancing habitat quality for pollinators [34,59,91] .

However, the absolute magnitude of these co-benefits is sensitive to site-specific characteristics, such as soil
texture and topography , as well as operational constraints like machinery maneuverability or maintenance
[92]