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What is the Value of Soil Organic Matter

September 07, 2023

Soil Organic Matter (SOM) contributes to the financial sustainability of farms by:

(1) Allowing for fertilizer reductions due to improved nutrient pathways.

(2) Improved water management from water retention.

(3) Pest suppression caused by increased biodiversity and plant health.

Improving SOM leads to cost savings by reducing reliance on external inputs, but also improves yield overtime increasing the bottom line.

Monetary Value of SOM = [|Fertility Value|+ |Water Value| + |Pest Value|]

X [Present Value of Future Benefit]

While calculations like these could be scrutinized for making assumptions, it is an important demonstration to compare short-term detrimental activities to long-term beneficial ones.

∆SOM = Change in SOM % (3% to 3.1% = .1)

A = Cost/Acre Fertilizer

B = Avg. Revenue/Acre of Crop

C = Avg # Water Stress Events/Cycle

D = Cost/Acre Pesticide

n = Number of Years of Evaluated Benefit

r = Interest Rate

Monetary Value = ∆SOM×[(.15×A)+(.10×B×C)+(.15×D)]×[(1-(1+r)^(-n))÷r]

Fertilizer Savings: +1% SOM -> ~15% Reduction in Fertilizer

While it is well understood that increasing SOM reduces fertilization requirements, it is not often acknowledged that the liberated nutrients are due to microbial ecosystems. Nutrient pathways are opened when saprophytic microorganisms mineralize SOM and predatory organisms begin to graze. Additionally, organic matter have a high cation exchange capacity and can hold soluble fertilizer more efficiently than bare soil, reducing the leaching potential. We acknowledge that pH, CEC, and many other factors would play a part in fertilizer reductions, but for this calculation we would estimate that a 0.1% increase in SOM would result in a 1.5% Fertilizer Reduction.

Water Management: +1% SOM -> 10% Yield Increase multiplied by the number of Water Stress Events

Increasing SOM will increase your soils water holding capacity. This allows your crop to access water between rain or watering events contributing to a more robust crop. Additionally, an increase in SOM will result in more water availability for microbial biomass and fungal networks. These networks contribute to root development and soil structure, thereby reducing the erosion potential of your soil during a high rain event.

Dale Strickler’s Drought Resilient Farm has great data quantifying SOM’s impact on water retention. In his book he shows that a 1% increase in SOM will result in approximately 0.4inches-/ft of moisture retention, and he demonstrates that yield of various Row Crops is increased after the minimum threshold of water is provided. In Corn for example, Strickler shows that that after the threshold is reached, each addition inch of moisture yields 16.9 bushels (approximately 10%? of the average US corn farmer yield of 175 bushels/acre)

Even if a plant’s roots only expand into 2.5 cubic feet of soil, then 1% increase in SOM would result in an additional 16.9 bushels, or 10% yield increase.

It is important to note that the benefit compounds in dry areas since water will be available in the soil for longer after a rain event. For those who irrigate, you may look at the efficiency of water holding capacity vs. irrigation costs.

Pest Suppression: +1% SOM -> ~%15 Savings in Pesticide and fungicide

While Management techniques such as no-till, composting, and cover crops do not necessarily target pests, they do contribute to a more diverse biological profile within the soil. Biodiversity results in resiliency, and this comes through mechanisms like ‘Predation’ - Any rise in pest pressure will result in a rise in its predator, if the predator exists.

There are many microorganisms that produce antagonistic chemicals that help to control pests and diseases, and their populations are supported by SOM. Other beneficial species like nematodes such as Butlerius sp that consume root feeding nematodes, and Ladybugs which regulate harmful aphid populations also thrive in higher SOM soils. With improved SOM and biodiversity, your crop will better resist pests and diseases leading to reductions in chemical applications.

In summary, too often are agricultural products and practices evaluated for their impact over one growing season, when their benefit or detriment is experienced over decades.

These rough assumptions should encourage you to include regenerative practices like cover cropping, roller crimping, and composting while avoiding detrimental practices like tilling and burning of crop residue.

Lastly, while it is not included in the equation, building organic matter in soil has the potential to store large amounts of carbon, helping to lower greenhouse gas levels. It is also feasible that in the near future, carbon credits may play a financial role in farming decisions, further incentivizing practices that support soil health.

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