Imagine there is a small island, like Malta, and the ecosystem has no external inputs (no fertilizer delivery, etc).
What does a sustainable plant based agriculture system look like? Are there already existing examples?
I’m very interested in how top soil is maintained without external fertilizer inputs?
One area of concern, I have, with modern monocrop farming techniques is the depletion of top soil, with something like 60 crop cycles left before we are current system falls over.
The industrial production of fertilizer is only about a century old (Haber-Bosch process for nitrogen fertilizers). Fertilizers are mainly concerned with nitrogen, phosphorus and potassium.
Before industrial fertilizers existed, people replenished the soil with:
Crop rotation works, because there are also natural processes which replenish these nutrients. For example, this is the nitrogen cycle:
https://en.wikipedia.org/wiki/Nitrogen_cycle
In particular, you can plant legumes, which will naturally bring nitrogen into the ground.
Either plant them as part of your crop rotation, or you can also plant e.g. potatoes and beans close together to continually replenish the nitrogen.
My understanding is that manure, and the crop rotation (three field system) both rely on animals; Does composting provide enough to replenish the soil sustainably?
The Three Sisters method, https://www.nal.usda.gov/collections/stories/three-sisters, has a ruminant cycle in it as well I believe.
I’m not sure, are ruminants acceptable as part of a plant based ecosystem?
No animal exploitation necessary. Humanure can return fertility to the soil, and syntropic agriculture takes a successional approach to crop rotation, building fertility over time.
That looks really cool. Thanks for the great references.
I watched a couple videos about it, and I think I understand the major themes. Where does the biomass come from that’s being referenced? Is external fertilizer needed after the food for us to set up? Is it self-sustaining, or does it need external inputs?
Referenced where exactly? Biomass in humanure comes from… well, your rear end. Biomass in syntropic agriculture is formed through photosynthesis, either in the plants deliberately grown on the farm or in native species used for chop-and-drop.
Unless the soil is severely depleted of micronutrients (e.g. calcium, magnesium, trace minerals), no external fertiliser should be required. Carbon comes from photosynthesis, nitrogen comes from microbial fixation, and phosphorus and potassium are usually not the limiting nutrients, but even in areas where they are, the only fertiliser needed to replenish them is ash. All of the people destroying the forest for fuelwood and charcoal are making plenty of fertiliser for you to use! (I’m not familiar with Malta specifically, but there seems to be some of this happening there as well.)
Ideally, a syntropic farm should cycle nutrients similarly to natural forest. Is a forest ecosystem self-sustaining, or does it need external inputs?
Hmm, I’m definitely out of my depth with that question.
Personally, I wouldn’t expect animals to perform a vital chemical transformation, since plants are likely to need the same form of nutrients for growing like a fully grown plant would contain when it goes onto the compost.
I guess, the animals may eat grass or hay, which’s nutrients then get concentrated onto the field with their manure. It doesn’t typically happen that all the human manure is delivered back onto the field, so you would lose nutrients with each harvest. So, it’s probably good to cut grass/hay specifically for composting. to help close the cycle more quickly.