The Problem with “More Is Better”
A study led by Dr. Swarnali Mahmood, tested a common assumption in soil health assessment: do higher indicator values consistently represent better soil function and greater crop productivity? Using bahiagrass pastures as a model system, the researchers found that the answer depends strongly on drainage conditions.
Many soil health frameworks use a “more is better” scoring approach for indicators such as soil organic matter, mineralizable carbon, and water-extractable organic carbon. Under this approach, higher values receive higher soil health scores because they are assumed to represent greater biological activity, nutrient cycling, carbon storage, or resilience.
This interpretation is often reasonable, but it assumes that indicator values increase for the same reasons across all fields. In reality, soil properties are influenced by both management and inherent site conditions, including soil texture, landscape position, climate, and drainage.
Drainage is especially important because it can affect soil aeration, organic matter decomposition, nutrient availability, root growth, and plant productivity. Consequently, a poorly drained field may have relatively high values for some carbon-based indicators while remaining less productive.
Under adequate soil moisture, aboveground bahiagrass biomass was positively associated with several soil indicators. This finding suggests that soil fertility and biologically active carbon pools can provide useful information about pasture productivity under favorable growing conditions. However, these relationships do not prove that increasing any one indicator will automatically increase forage production.
The relationships changed under simulated drought. None of the evaluated soil health indicators was significantly associated with the ability of bahiagrass to retain biomass during drought stress.
Drainage also influenced how the indicators related to farmer-observed productivity. When the most and least productive pastures had similar drainage conditions, the more productive fields tended to have higher soil organic matter, potassium, and water-extractable organic carbon. In these comparisons, the “more is better” interpretation generally agreed with farmer observations.
However, when the least productive pasture was more poorly drained, the pattern changed. In some comparisons, the poorly drained, less productive fields contained more soil organic matter and water-extractable organic carbon than the better-drained, more productive fields.
Key Takeaway
Higher soil health indicator values do not always represent better soil function. Drainage can increase some carbon-based measurements while simultaneously restricting plant productivity.
The study supports a more contextual approach to soil health assessment. Rather than asking whether a value is simply high or low, farmers, laboratories, and advisers should ask why the value is high, what soil function it represents, and whether it corresponds with actual field performance.
Reference: Mahmood, S., Dubeux, J. C. B., Jr., & Lin, Y. (2026). Drainage conditions complicate the “more is better” paradigm in soil health assessment. European Journal of Soil Science, 77(3), e70364. https://doi.org/10.1111/ejss.70364.
