MAXIMIZE Photosynthesis and minimize tillage; Two Principles for Managing Soil Health.

By Andrew McGuire, CSANR Senior Extension Fellow.

There is no shortage of advice on soil health. Cover crop cocktails, reduced tillage, livestock integration…the list goes on. With so many options, it’s hard to know what matters most. Two principles can cut through all that, both grounded in the most influential factor for soil health: soil organic matter. These principles can help you make sound soil health decisions and avoid unsound advice.

Stay in Business

Before I get to the principles, there is one condition that must be met regardless of the value of any soil health practices or products: the farm must stay in business. Every soil health decision is made within the constraints of economic survival. It makes no sense to have the best soil in the county while headed to the auctioneer. If we acknowledge this first, then the principles become realistic guides rather than unyielding dogma.

Two Principles of Soil Health

Soil health management can be distilled into two principles: MAXIMIZE Photosynthesis and minimize tillage.

Maximizing photosynthesis is all about managing plants to intercept sunlight to power their growth (Janzen, 2015). Plant biomass—the carbohydrates produced by photosynthesis—feeds both us and everything in the soil. The more crop biomass we can grow, the more energy there is in the system for all the biology.

So, fill the space you have with plant growth. Aim for a full-time, full canopy as much as possible. And fill the time you have with plant growth, year-round plant growth, although I doubt we could tell if you missed a couple of weeks over the course of a year. To fill time and space will require a soil with sufficient nutrients, optimum pH, and structure conducive to seedling emergence and root growth, which brings us to the second principle.

Minimizing tillage focuses on reducing soil disturbance. Of all our farming practices, tillage is the largest disturbance of the soil, bigger than pesticides and fertilizers. Tillage damages soil structure and reduces protective residue cover. Minimizing tillage maintains soil structure and, by leaving crop residues, keeps the soil protected from erosion.

Together, Maximize Photosynthesis and minimize tillage provide the foundation of soil health: building or maintaining soil organic matter.

Soil Health≈Soil Organic Matter

Soil organic matter affects nearly every aspect of soil functioning: microbial activity, aggregation, infiltration, drainage, resistance to compaction, surface crusting, nutrient cycling, etc. (Viaene et al., 2025). Although there is no clear threshold of soil organic matter levels (SOM) for soil health (Loveland & Webb, 2003; Prout et al., 2020), having more is better than having less.

There is a simple equation for changes in soil organic matter levels:

ΔSOM (change in SOM) = INPUTS – LOSSES

Inputs are crop biomass, the result of photosynthesis (Janzen et al., 2022; Rubio et al., 2025). Losses are the decomposition of existing soil organic matter, which can be beneficial or detrimental (Janzen, 2006). Feeding soil microbes is a large but beneficial loss, while the tillage-induced loss of soil organic matter and disruption of soil structure is the main detrimental loss. Maximizing photosynthesis increases INPUTS and minimizing tillage reduces the most damaging LOSS of SOM – the principles affect both of the factors in this equation, favoring an increase of SOM over time.

Translate this back to the dials above: Maximize Photosynthesis controls the Inputs, Minimize Tillage controls the Losses. Combined, the Max and min principles produce a soil with the organic matter concentrated at the soil surface, where it can do the most good. The flow of carbon through the soil is nearly continuous, both from plants and from decaying crop residue. In the long-term, and sometimes in the short-term, these two principles can address real soil problems. The practices you already use to manage pH, nutrients, and pests all contribute to maximizing photosynthesis.

Practices from Principles

These are principles; they tell you what you want from the practices you choose. Each principle can be implemented through different practices depending on your system. Here is a partial list of practices for each principle. Some practices facilitate other practices and some address both principles.

Practices that Help Maximize Photosynthesis:	Practices that Help Minimize Tillage, in descending order of effectiveness:
Relay crops	No-till/Direct seeding
Cover crops	Strip-till
Perennial crops	Vertical tillage
Overwintering crops and cover crops	Non-inversion tillage
Manure/compost, imported photosynthesis
Practices that facilitate the above practices:	Practices that facilitate the above practices:
Livestock grazing	Livestock grazing
Crop rotation	Crop rotation
Nutrient management	Residue management
Pest management	Weed management
Irrigation
No-till, strip-till, practices that reduce field prep time between crops

These principles also assume that erosion, which is the opposite of building soil, is minimized. You cannot build health into soil that is losing ground.

Back to Staying in Business

Of course, it’s not that simple. These principles must be adjusted for many factors: climate, markets, economics, crops, pests, soils, regulations, equipment, technology, etc. and all the inherent trade-offs of agriculture. The constraints of “staying in business” often mean that the Maximize knob will never be at maximum, and the minimize knob never at minimum. This is what the equation reflects: a system optimized to your real constraints, not someone else’s ideal of soil health.

Two principles, Many Applications

That’s it, two principles. You have two dials to work with: turning one up and the other down can mean increased soil organic matter and soil health, all within the real-world constraints of your farm.

References

Janzen, H. H. (2006). The soil carbon dilemma: Shall we hoard it or use it? Soil Biology and Biochemistry, 38(3), 419–424. https://doi.org/10.1016/j.soilbio.2005.10.008

Janzen, H. H. (2015). Beyond carbon sequestration: Soil as conduit of solar energy. European Journal of Soil Science, 66(1), 19–32. https://doi.org/10.1111/ejss.12194

Janzen, H. H., van Groenigen, K. J., Powlson, D. S., Schwinghamer, T., & van Groenigen, J. W. (2022). Photosynthetic limits on carbon sequestration in croplands. Geoderma, 416, 115810. https://doi.org/10.1016/j.geoderma.2022.115810

Loveland, P., & Webb, J. (2003). Is there a critical level of organic matter in the agricultural soils of temperate regions: A review. Soil & Tillage Research, 70(1), 1–18.

Prout, J. M., Shepherd, K. D., McGrath, S. P., Kirk, G. J. D., & Haefele, S. M. (2020). What is a good level of soil organic matter? An index based on organic carbon to clay ratio. European Journal of Soil Science, n/a(n/a). https://doi.org/10.1111/ejss.13012

Rubio, V., Núñez, A., Berger, A., & van Es, H. (2025). Biomass inputs drive agronomic management impacts on soil health. Agriculture, Ecosystems & Environment, 378, 109316. https://doi.org/10.1016/j.agee.2024.109316

Viaene, J., Quataert, P., Joos, L., De Tender, C., Debode, J., & Vandecasteele, B. (2025). Link Between Soil Organic Carbon and Microbial Soil Health Indicators in Arable Fields: Management and Spatial Drivers. European Journal of Soil Science, 76(6), e70250. https://doi.org/10.1111/ejss.70250