Matt’s video prompted this reply. 🙂 Now you may know my views on compost, well…
In the video above they show a comparison of the effect of soil imprinting on run-off vs not imprinting on the left. Soil imprinting is a wonderful way to start a garden if you don’t have much compost or organic matter in topsoil, say in a dry climate. Throw what compost you have in those troughs, or not. Soil imprinting simply makes your soil look like one big egg carton helping to collect rain and wind debris. Soil moisture is the single biggest factor when it comes to building soil carbon and fertile productive soils, living plants and the microbes they host in the soil are the other. Harvesting that water where plants can use it to suck carbon from the air and feed it to soil microbes is critical, but so is the material that blows into the troughs. This material is very nitrogen rich, like the air that blows it in, and tends to have a high cation exchange capacity. It’s why weeds thrive in cracks and crevices.
This is mulching in place.
Live in a wet climate? Try planting in the peaks.
Cattle, bigfoot and astronaut grazing systems have a similar effect to soil imprinting, this can be a useful feature in intensive rotational grazing systems, so long as you have enough astronauts…
Once you’ve imprinted, simply broadcast seeds and what compost you have into the troughs where water and debris blown by wind and rain collect and away you grow.
And while compost is great and helps get plants and a garden get started, what really gets the party going after that is when you chop and drop or roll and crimp just when plants flower and reach peak biomass. Studies have shown you get 3x more microbial biomass carbon and nitrogen than from compost if you chop a cover crop. More if you roll and crimp it, and even more on sandy soils.
It’s the leaching of soluble compounds from fresh litter that helps achieve this by feeding microbes that glue soil particles together and make houses for themselves, along with the moisture management properties of the bulk material once soluble nutrients are leached. Rolling and crimping helps by slowing the moisture loss.
I’ve previously written that when mulching ideally mulch should have a C:N of less than 50:1 to prime soil carbon, otherwise until the soil interface layer with mulch has biodegraded enough it will have a negative carbon priming effect that leads to problems like nitrogen deficiency. Planting legumes can help here if you’ve made that mistake, so can running chickens over the mulch, or simply moving it aside to expose the soil to more air.
Ultimately, we should aim for the Soil Carbon Continuum approach that consists of increasing C:N and chip sized mulch layers. Increasing in chip size is similar in many ways to the soil imprinting above.
It’s not just plants that need layers in the permaculture world.
I like to start with soil imprinting, then compost, fresh plant litter, dry leaf/twig/bark mulch, branch mulch, sapwood mulch and then heartwood mulch layers. Each increasing in C:N ratio and halving the amount applied with each layer. All followed by a living root.
Because ultimately it’s the inputs that drive microbial diversity and power the soil food web, not the other way around. Fungi for example need a continuous supply of carbon to grow and fruit. In forests massive old growth trees do this in large quantities when they suck carbon from the atmosphere. It’s been shown that adding nitrogen fertilizer disrupts this feeding of soil microbes by trees, upsetting the highly tuned ecosystems.
So don’t forget the living root in those layers above. They host symbiotic microbes like mycorrhizal fungi that can shunt nutrients and water at 3mm per hour, that’s 72mm or 3″ a day!
And roots pump the carbon in the air into the soil to feed soil microbes, but only up to a point. What’s that point I hear you ask? It’s soil moisture dependant. It’s been shown that plants exhale more carbon than they sequester when when moisture deprived during droughts. And increasing carbon in our atmospheres means plants thirst for more water leading to even worse droughts in some climates as plants suck that water up.
That’s it. Follow the path of the living root.
In another post I’ll cover some different forms of carbon that make up the soil carbon continuum and play different roles and why we want diversity there too.