Soil Protein as an Indicator of Soil Health

Soil health is an important part of agricultural production and entails a balance of soil physical, chemical, and biological properties. Biological indicators of soil health are important to measure but which ones merit spending valuable resources measuring?

Here I’ll point out a few highlights of research by Naasco et al. (2024) on a soil health indicator called ACE (autoclaved-citrate extractable) protein. A healthy soil is a living system that sustains biological productivity (FAO 2008). Plants obtain nutrients from the soil, of which nitrogen is essential. Most of the nitrogen in soil is bound up in organic matter and released over time as it breaks down. Naasco et al. (2024) explain that protein constitutes the largest portion of organic nitrogen in the soil. Thus, soil protein has a strong connection to soil health.

Why bring up ACE protein? While there are other indicators of soil nitrogen, most have significant drawbacks in assessing how well a farmer’s practices are working to manage soil nitrogen. Nitrate, for example, is readily leached from the soil, so values can change quickly in response to rainfall and irrigation events. Total nitrogen, on the other hand, is so stable that it doesn’t respond well to seasonal management changes. ACE protein is a relatively new test that provides a much better understanding of how farming practices affect soil nitrogen. If you are doing agricultural research and are looking for laboratories to send soil samples to, you’ll want to be aware of ACE protein. The Cornell Soil Health Lab, for instance, offers the ACE Protein Test at the cost of 30 USD per sample. Hopefully, more labs worldwide will offer the test.

Naasco et al. (2024) found that perennials and diverse plantings resulted in soil protein levels that were two to four times higher than annual cropping and monoculture systems. They pointed to numerous studies showing that perennials and crop diversity contribute to soil organic matter via their root systems. Their paper points to other studies on fine roots (e.g., Martin and Sprunger, 2021), those with a diameter of less than 2 mm. Fine roots interface between the soil and the plant and add organic matter through the release of various exudates (secreted chemicals) into the soil and decomposition. Naasco et al. (2024) also discussed the relationship between soil protein and soil structure. It all connects!

I trust these concepts are helpful to you in thinking about an agroecological approach to nitrogen management that fits your context. Even if you don’t have access to a laboratory that can measure soil protein, you can still implement concepts shown to improve soil health such as increased crop diversity.


FAO 2008. An international technical workshop Investing in sustainable crop intensification-the case for improving soil health. Integrated Crop Management Vol.6-2008. FAO, Rome: 22-24 July 2008

Hurisso, T.T., D.J. Moebius-Clune, S.W. Culman, B.N. Moebius-Clune, J.E. Thies, and H.M. van Es. 2018. Soil protein as a rapid soil health indicator of potentially available organic nitrogen. Agricultural & Environmental Letters 3:180006.

Martin, T. and C.D. Sprunger. 2021. Belowground dynamics influence nitrogen cycling and crop productivity in diversified corn systems. Frontiers in Sustainable Food Systems 5-2021.

Naasco, K., T. Martin, C. Mammana, J. Murray, M. Mann, and C. Sprunger. 2024. Soil protein: a key indicator of soil health and nitrogen management. Soil Science Society of America Journal 88:89-108.


Getting good insights from nitrogen assays is often challenging. Getting a glimpse at protein N helps us hone in on N ready to cycle to our plants, and is maybe not a bad proxy for assessing the soil food web. Thank you for sharing this approach, Mr. Motis!

I would offer one caveat that you may well find you have increasing levels of soil protein without and accompanying increase in plant-available N. That would be the case where bacteria, fungi, and algae are rising in the soil, but the ecosystem lacks the predators/nutrient-cyclers necessary to mineralize those proteins into plant-available NH4s and amines.

If I were measuring soil protein and not seeing the changes in crop outcomes I expect, I would look for someone with a microscope who can do an assesment of the different functional groups in the soil ecosystem. That approach could offer a soil protein estimate as well as it correlates with biomass, though not as precise as ACE protein.

Peace be with y’all.


Thank you Scott. Your thoughts are very helpful in giving a more complete understanding of what can be learned from soil protein measurements and about nitrogen cycling in the soil in general. Much appreciated!