Bringing Soil Back to Neutral: The Hidden pH Fix That Stores Carbon and Boosts Crop Yields

For decades, agricultural scientists have treated soil acidity and soil carbon as two separate problems demanding two separate solutions. A sweeping new synthesis published in Advanced Science now shows they are deeply, quantitatively intertwined — and that fixing one can quietly pay for the other. By analyzing 251 field trials from around the world, researchers demonstrate that when farmers replace part of their synthetic fertilizer with organic amendments such as manure, biochar, or compost, the soil’s pH drifts back toward neutrality, and that chemical shift alone — independent of the carbon added by the amendments — locks away a substantial amount of soil organic carbon while lifting crop yields.

The scale of the problem the study addresses is staggering. Roughly half of the world’s croplands now have a pH below 5.5, a consequence of decades of intensive synthetic nitrogen fertilization. This acidification has stripped away up to 20 percent of soil organic carbon and cut average yields by about 14 percent. At the opposite extreme, nearly 397 million hectares of alkaline cropland are losing carbon at a rate of about 3.47 tonnes per hectare per year. Soil organic carbon is the backbone of soil health: it stabilizes structure, regulates water retention, and drives nutrient cycling, while pH governs nutrient availability, microbial activity, and ion toxicity. When both deteriorate simultaneously, food production and climate mitigation suffer together.

The central methodological challenge has always been disentanglement. Organic amendments do two things at once: they add exogenous carbon directly to the soil, and they shift pH. Any measured increase in soil organic carbon under organic substitution could therefore come from the carbon you put in, from the pH change itself, or from some interaction of the two. Previous studies could not separate these contributions, leaving a critical gap in predictive carbon models and in the design of climate-smart farming policies. The research team, led by scientists at Northwest A&F University in China, built a weighted mixed-effects meta-analytic framework that statistically partitions the carbon increment attributable solely to pH change after controlling for exogenous carbon inputs.

To validate this statistical partitioning, the researchers compiled a second, independent dataset of 29 liming experiments in which pH was adjusted without any organic carbon addition. The results aligned strikingly. In acidic soils, organic substitution raised pH by 5.6 percent on average and increased total soil organic carbon by 22.2 percent — and up to 15.0 percent of that accrual was attributable to pH amelioration alone. The lime-only experiments, where no organic carbon was added, produced a comparable pH-specific carbon gain of 6.8 percent, confirming that the effect is real and not an artifact of the added material.

The pattern differed sharply by initial soil condition. In neutral soils, total carbon accrual reached 28.2 percent, with 9.2 percent driven by pH movement. Alkaline soils showed the largest composite carbon gain at 35.7 percent, yet the pH-specific share was more modest at 4.1 percent, reflecting the smaller absolute pH shift of just 0.6 percent achieved in those buffered, carbonate-rich systems. Crucially, the direction of the relationship held everywhere: carbon accrual rose as pH moved toward neutrality, whether that meant raising it in acidic soils or lowering it slightly in alkaline ones.

The mechanism, the study finds, runs through the soil’s microbial inhabitants. Random forest analysis identified microbial biomass and pH itself as the principal drivers of pH-mediated carbon accrual, and structural equation modeling revealed a clear cascade: pH amelioration enhances microbial biomass, which in turn drives soil organic carbon accumulation, which ultimately contributes to yield gains. In acidic soils, microbial biomass increased by 42.2 percent under organic substitution, and lime-only trials corroborated a 35.9 percent biomass increase from pH adjustment alone. Microbial biomass was the strongest biotic driver of carbon accrual in acidic soils, explaining 54.4 percent of its variance there, with weaker but still significant effects in neutral and alkaline soils.

The chemistry behind this microbial carbon pump is elegant. In acidic soils, raising pH suppresses acid-catalyzed hydrolysis that would otherwise chew through organic macromolecules like polysaccharides. It also promotes the deprotonation of carboxyl groups, strengthening their bridging with polyvalent cations such as calcium and fostering microaggregate formation that physically shields carbon from decomposition. Microbial residues themselves — bacterial peptidoglycans, fungal chitin, extracellular polymeric substances — contribute recalcitrant carbon that persists for decades. In alkaline soils, a slight shift toward neutrality weakens excessive deprotonation of organic functional groups, reduces the mobility of dissolved organic carbon, and helps colloids stay aggregated rather than dispersing, all of which favor carbon retention in the solid phase.

The yield story is equally compelling. Composite yield gains reached 24.6 percent in acidic soils, 15.3 percent in neutral soils, and 9.5 percent in alkaline soils, and the carbon accrued through pH amelioration accounted for 8.6, 5.1, and 8.1 percent of those gains respectively. Liming trials showed pH adjustment alone could raise yields by 45.4 percent, underscoring how powerful the nutrient-availability effects are — raising acidic soil pH dramatically improves phosphorus uptake, while lowering alkaline pH frees up iron and zinc that would otherwise be locked into insoluble hydroxides. Every 10 grams per kilogram increase in soil organic carbon also adds available water to the profile, improving drought resilience, and global modeling suggests large-scale carbon accrual could shave temperatures slightly, indirectly protecting cereal yields from heat stress.

Geographically, the benefits were universal but uneven. Europe showed the strongest pH-driven carbon accrual at 27.4 percent, likely a product of temperate hydrothermal conditions and conservation-oriented management such as cover cropping and reduced tillage. Africa posted the highest yield gains at 9.9 percent, plausibly because low-fertility, aluminum-toxic croplands offer the greatest marginal returns when acidity constraints are lifted. Among amendment types, biochar, manure, and soil conditioners all shifted pH effectively, while straw return alone failed to move pH significantly and delivered correspondingly weaker carbon and yield benefits — a notable rebuttal to earlier suggestions that straw return worsens acidification.

The authors are candid about limitations: their partitioning is statistical attribution rather than strict experimental causation, and data on soil aggregate stability and root traits were too sparse to test every proposed pathway. Still, the implications are concrete. Acidic soil regions should be prioritized for pH management in carbon sequestration programs, and carbon crediting frameworks — which currently reward organic inputs but ignore microhabitat optimization — should recognize pH-mediated microbial carbon stabilization as a legitimate sequestration pathway. As the world grapples with the trilemma of feeding a growing population, restoring degraded cropland, and flipping agriculture from carbon source to sink, this study suggests that one of the most powerful levers may be the humblest of all: getting the soil’s chemistry back to neutral.

Subject of Research: Soil pH amelioration under organic fertilizer substitution and its effects on soil organic carbon sequestration and crop yields

Article Title: Soil pH Amelioration Synergizes Carbon Accrual with Yield Gains Under Organic Substitution

Article References: Dong, X., Yao, Y., Han, B., Zhong, Y., Li, B., Li, M., Dai, Y., & Li, Z. (2026). Soil pH Amelioration Synergizes Carbon Accrual with Yield Gains Under Organic Substitution. Advanced Science, Article e78051. https://doi.org/10.1002/advs.78051

Image Credits: AI Generated

DOI: 10.1002/advs.78051

Keywords: soil pH, soil organic carbon, organic substitution, carbon sequestration, crop yield, microbial biomass, meta-analysis, soil acidification, liming, climate-smart agriculture, biochar, sustainable intensification