Sure, compost adds nutrients. But that might be this soil amendment’s least important function.
Quite often, articles will mention compost as a replacement for some or all of the nutrients that might be provided to plants through applications of synthetic (man-made) fertilizers.
That’s certainly true. Compost delivers the macronutrients nitrogen, phosphorus, and potassium (NPK), plus a slew of plant-essential micronutrients that are missing from most synthesized fertilizer products. Compost provides plants with a wholesome, well-rounded meal, not the nutritional equivalent of junk food.
But what these fertilizer-focused articles rarely mention is the fact that the real value in compost use is not related to feeding plants, but to feeding soil … and soil does require a wholesome diet to function as a true soil and not a dead substrate.
Providing plant nutrients is just one of many soil functions. Worms and other creatures that live in healthy soils help to physically break down food sources, then microbes take over to convert that food into plant-available form.
Both physical and microbial conversion depend on a soil environment that can support those lifeforms. If the soil is chronically too wet, too dry, too compacted – yada, yada – then it can’t support a healthy soil ecosystem. That plot of ground may not be soil at all, but lifeless dirt.
To countermand the impacts of human activity, disturbed soils require a regular program of replenishment that includes organic matter and microbes. Compost provides both. Compost feeds soil.
Then, when it rains, soil retains that water, reducing runoff. When runoff is reduced, so is erosion, sedimentation, and water pollution. Because soil microbial activity also degrades pollutants, any stormwater that does run off is cleaner.
That same microbial activity can help neutralize some soil-borne diseases, too.
Improving plant nutrition, aiding in disease control, reducing water pollution, and retaining water are all important soil functions.
But wait, there’s more.
The build-up of greenhouse gases in the earth’s atmosphere is cause for concern. As more greenhouse gases flood the atmosphere, temperatures increase.
This rise in global temperatures influences many things, erratic and extreme weather being one of the most visible. Subsequent climate shifts can impact people, crops, and livestock for hundreds of years.
When used to amend soils, compost sequesters carbon. This means the soil will act as a carbon “sink,” capturing and holding carbon in stasis – but only as long as the soil remains undisturbed. When the soil is tilled, that carbon is released.
Extensive use of compost for perennial crops and other long-term applications (grasslands, tree farms, utility easements, etc.) can positively impact atmospheric conditions by reducing greenhouse gases.
At the same time, the addition of compost rebuilds a topsoil layer that has been eroded or scraped away by farming, development, and other human activity. Since topsoil loss has been identified as a significant threat to planetary health, second only to population growth, its restoration is a global priority.
At a time when nearly a third of the world’s arable land has become unproductive in just a few decades, compost really can be that superhero swooping in to save topsoil, save water, save the atmosphere, and save the planet.