Soil as a Lead Indicator of the Global Goal on Adaptation (GGA)

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Scientific Legitimacy for Global Monitoring

Soil health, anchored by soil organic carbon (SOC) and its biological, chemical, and physical foundations, offers a rigorous, globally relevant set of indicators for tracking adaptation progress under the GGA while delivering mitigation co-benefits. Across continents and production systems, long-term experiments, syntheses, and regenerative case studies show that no/reduced tillage, cover crops, crop–livestock integration, pasture cropping, and agroforestry consistently:

• Increase SOC stocks (including deeper pools) and stabilize labile/recalcitrant fractions (Bayer et al., 2014; Thierfelder et al., 2013; Rodale Institute, 2020; Soils For Life, 2011; Soils For Life, 2012; Negi et al., 2025; Abán et al., 2025; Khangura et al., 2023; Mäder et al., 2025; Nguyen et al., 2023).

• Enhance water infiltration, holding capacity, and aggregate stability (LaCanne et al., 2021; Rodale Institute, 2020; Soils For Life, 2011; Soils For Life, 2012; Abán et al., 2025; Khangura et al., 2023).

• Improve biodiversity and biological activity, including microbial biomass, earthworms, and enzymes (LaCanne et al., 2021; Rodale Institute, 2020; Soils For Life, 2011; Abán et al., 2025; Bogušas et al., 2022; Khangura et al., 2023; Mäder et al., 2025).

• Boost yields stability and profitability under climate stress while reducing input dependence (Lotter et al., 2003; Thierfelder et al., 2013; LaCanne et al., 2021; Soils For Life, 2011; EARA, 2025; Bunch, 2025).

• Deliver mitigation co-benefits via carbon sequestration and reduced soil-driven GHG emissions (Kopittke et al., 2024; Khangura et al., 2023; Nguyen et al., 2023).

Indicators for soil tracking in the GGA

1. Soil organic carbon (SOC) stock and change rate

Evidence across systems shows SOC responds measurably to management and correlates with resilience and yield:

• Continuous no-till in Brazil’s soybean–maize system increased SOC in the top 0–20 cm and enhanced labile carbon. Each additional 1 megagram of SOC per hectare was associated with 11 kilograms per hectare more soybean and 26 kilograms per hectare more wheat (Bayer et al., 2014).

• In Zambia, conservation agriculture increased SOC by 12% in the top 0–30 cm compared to a 15% decline under conventional practices. Maize yields rose by 75 to 91% after four to six seasons (Thierfelder et al., 2013).

• A 40-year U.S. trial showed that organic manure systems maintained higher soil organic matter than conventional systems (Rodale Institute, 2020).

• Case studies from Australia reported significant SOC gains. Clover Estate saw a 45% increase in the top 150 mm, while Shannon Vale recorded a 203% increase to 500 mm depth, with most of the carbon in stable forms (Soils For Life, 2011; 2012).

• Agroforestry systems in the Indian Himalayas increased both surface and deep SOC. At 30–60 cm depth, SOC reached 33.52 megagrams per hectare, with labile carbon 33% higher than fallow plots (Negi et al., 2025).

• Perennial pastures with Brachiaria grass showed a 62% increase in SOC compared to bean monoculture systems (Abán et al., 2025).

• In Southeast Asia, SOC consistently increased under biochar, compost, manure, cover crops, crop rotations, and conservation tillage. Agroforestry systems showed 4 to 6% higher SOC than monocultures (Nguyen et al., 2023).

• A review of regenerative organic agriculture found SOC levels were 22% higher than in conventional systems across multiple experiments (Mäder et al., 2025).

• Systems combining no-till, residue retention, and crop diversification increased SOC by 0.1 to 0.3 megagrams per hectare per year. Regenerative agriculture systems sequestered between 0.3 and 0.8 megagrams per hectare per year in early years (Khangura et al., 2023).

Recommended metrics:

• SOC stock (Mg C ha⁻¹) at standardized depths (0–30 cm; optionally 30–60 cm), resampled every 3–5 years

• Annual SOC change rate (Mg C ha⁻¹ yr⁻¹)

2. Soil carbon fractions (labile and stable pools)

Labile carbon responds quickly to management and serves as a predictor of near-term productivity. Stable carbon fractions reflect durable sequestration and long-term resilience.

• Continuous no-till systems increased labile carbon, which correlated with improved resilience and crop productivity (Bayer et al., 2014).

• Pasture cropping and planned grazing practices led to increases in stable, non-labile soil organic carbon down to 500 mm depth (Soils For Life, 2012).

• Mulberry-based agroforestry systems in the Indian Himalayas showed labile carbon levels up to 33 percent higher than fallow plots (Negi et al., 2025).

Recommended metrics:

• Labile carbon fraction (percentage of SOC)

• Particulate organic matter

• Carbon Management Index (CMI)

3. Soil biodiversity and biological activity

Biodiversity underpins nutrient cycling, pest suppression, and structural stability.

• Regenerative almond systems showed significantly higher microbial biomass (total and bacterial), Gram-positive bacteria, Actinobacteria, invertebrate richness, earthworm abundance, and plant diversity. Yields remained comparable to conventional systems, while profits were twice as high (LaCanne et al., 2021).

• Long-term organic systems exhibited higher microbial activity and reduced soil compaction compared to conventional systems (Rodale Institute, 2020).

• Biological inoculants and biofertilizers improved pasture vigor and increased SOC at Clover Estate (Soils For Life, 2011).

• Perennial pasture restoration led to increases in microbial respiration (40 percent), microbial biomass carbon (38 percent), microbial biomass nitrogen (59 percent), glomalin-related soil protein (24 percent), enzyme activity (25 percent), and bacterial diversity (Abán et al., 2025).

• In a long-term Lithuanian study, crop rotations significantly increased earthworm abundance and biomass compared to monoculture rye. Earthworm biomass ranged from 2.4 to 13.5 times higher in diversified systems, with strong correlations to soil moisture and temperature. These biological improvements were linked to enhanced soil structure and resilience under variable climatic conditions (Bogušas et al., 2022).

• Adoption of regenerative agriculture practices resulted in earthworm density increases of 50 to 200 percent and microbial biomass increases of 20 to 60 percent (Khangura et al., 2023).

• A literature review of regenerative organic agriculture reported microbial biomass carbon levels 133 percent higher than conventional systems (Mäder et al., 2025).

Recommended metrics:

• Microbial biomass carbon (mg C kg⁻¹ soil)

• Soil respiration rates

• Biodiversity indices (microbial and invertebrate richness)

4. Soil physical health (structure, compaction, water metrics)

Physical properties determine erosion risk, root penetration, and water resilience:

• In regenerative almond orchards, water infiltration was six times faster than in conventional systems (LaCanne et al., 2021).

• Long-term organic plots showed 15 to 20 percent higher infiltration rates and reduced soil compaction. However, caution is warranted, as chemical-intensive no-till systems may also lead to compaction (Rodale Institute, 2020).

• At Clover Estate, improved soil structure reduced irrigation water use per unit of animal weight by 25 percent and halved energy required for pumping. Total water use was approximately 5 to 6 megaliters per hectare per year, compared to the typical 7 to 8 megaliters for deep sandy soils (Soils For Life, 2011).

• At Shannon Vale fields in Australia, gains in SOC increased water holding capacity by an estimated 120,000 to 150,000 liters per hectare per year (Soils For Life, 2012).

• Under perennial pasture systems, aggregate stability increased by 76 percent, and water holding capacity rose significantly (Abán et al., 2025).

• A literature review of regenerative organic agriculture found that infiltration improved by more than 30 percent with residue cover and no-till. Water holding capacity improved by 10 to 20 percent with higher SOC. A one percent increase in soil organic matter can raise available water holding capacity by up to 1.5 percent, depending on soil texture (Khangura et al., 2023).

Recommended metrics:

• Infiltration rate (mm/hr)

• Bulk density (g/cm³)

• Plant-available water holding capacity (mm)

• Aggregate stability (percentage)

5. Productivity and profitability under climate stress

Adaptation performance is reflected in yield stability and net margins under variable climate.

• In multiple drought years, organic maize outperformed conventional maize by 38 to 137 percent in legume/manure systems, with water capture during heavy rains being nearly double, and soybeans also exceeded conventional yields (Lotter et al., 2003).

• In Zambia, conservation agriculture increased maize yields by 75 to 91 percent compared to conventional methods. These gains were supported by improvements in SOC and residue retention (Thierfelder et al., 2013).

• Regenerative almond systems achieved similar yields to conventional orchards but delivered twice the profit due to reduced input costs and enhanced ecosystem services (LaCanne et al., 2021).

• At Clover Estate, stock output increased by 33 percent while water and chemical inputs declined significantly (Soils For Life, 2011).

• A long-term study in Lithuania found that winter rye monoculture yielded 22.5 percent less than rotational systems. When winter rye followed two years of perennial grasses, yields were 27 percent higher than in monoculture plots. (Bogušas et al., 2022).

• Farmer-led case studies across EU sites reported gross margins between 20 and 187 percent higher than conventional systems, despite occasional yield reductions. Use of synthetic inputs declined by 62 to 100 percent (EARA, 2025).

• Maize–mucuna systems yielded approximately 30 percent less than mechanized maize but achieved higher profitability per bushel. Soil organic matter ranged from 12 percent to a depth of 35 cm (Bunch, 2025).

• In India, treatments combining NPK with farmyard manure showed the greatest microbial resilience under heat stress (Kumar et al., 2013).

Recommended metrics:

• Yield stability index (stress-year yield / average yield)

• Input intensity (fertilizer, pesticide, irrigation)

6. Soil greenhouse gas (GHG) balance

Soils act as both sources and sinks of greenhouse gases. Tracking net flux ensures that adaptation delivers mitigation co-benefits and avoids unintended trade-offs.

• Net anthropogenic soil emissions account for approximately 15 percent of global radiative forcing from well-mixed greenhouse gases. These include carbon dioxide (74 percent), nitrous oxide (17 percent), and methane (9 percent) (Kopittke et al., 2024).

• Conventional systems tend to have higher levels of inorganic nitrogen, which increases the risk of nitrate leaching and nitrous oxide emissions. In contrast, organic systems reduce nitrate percolation and improve water infiltration (Rodale Institute, 2020).

• A literature review of regenerative organic agriculture reported net greenhouse gas reductions ranging from 0.5 to 1.5 tonnes of CO₂-equivalent per hectare per year. These reductions were achieved through SOC sequestration and lower fuel use. Methane emissions were commonly reduced with biochar applications, while results for carbon dioxide and nitrous oxide varied depending on context (Khangura et al., 2023; Nguyen et al., 2023)

Recommended metrics:

• Net soil GHG flux (CO₂, N₂O, CH₄) in CO₂-equivalent per hectare per year, where feasible

• Validated proxies: inorganic nitrogen pools, nitrate leaching, residue cover, fuel use intensity

Measurement guidance for global monitoring

Soil health provides a scientifically grounded and globally scalable framework for tracking adaptation under the Global Goal on Adaptation (GGA). It integrates chemical, biological, physical, and functional dimensions that are responsive to management and relevant across diverse agroecosystems.

To ensure consistency across regions and production systems, the following six indicators are recommended for inclusion in national and global monitoring frameworks:

1. Soil Organic Carbon (SOC) Stock and Change Rate tracks carbon accumulation and loss over time, reflecting long-term resilience and productivity.

2. Soil Carbon Fractions (Labile and Stable Pools) measures short-term responsiveness and durable sequestration potential through labile and recalcitrant carbon pools.

3. Soil Biodiversity and Biological Activity captures microbial biomass, respiration, and invertebrate richness as key drivers of nutrient cycling and soil health.

4. Soil Physical Health (Structure, Compaction, Water Metrics) assesses infiltration, bulk density, water holding capacity, and aggregate stability to evaluate erosion risk and climate resilience.

5. Productivity and Profitability Under Climate Stress evaluates yield stability, input efficiency, and net margins under variable climatic conditions.

6. Soil Greenhouse Gas (GHG) Balance accounts for net emissions or sequestration of CO₂, N₂O, and CH₄, with validated proxies where direct measurement is not feasible.

Policy relevance to the GGA

Embedding soil indicators in national adaptation Monitoring and Evaluation enables countries to:

• Quantify adaptation outcomes, including improved water capture, yield stability, and reductions in erosion and compaction. 

• Demonstrate mitigation co-benefits such as SOC accrual, reduced nitrous oxide risk, and deep carbon storage through agroforestry and pasture systems. 

• Advance equity and profitability by supporting smallholder systems that reduce input dependence while maintaining or improving yields.

• Align climate finance and incentives with measurable soil outcomes and farm economics, including the adoption of cover crops, crop rotations, grazing intensity management, and agroforestry.

Recognizing soil as climate-critical infrastructure allows countries to bridge adaptation and mitigation goals, empower farmers, and unlock co-benefits across sectors.

Bibliography

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