Do we need livestock for fertility?
Some people get the idea from some new Permie and Regenerative Ag sources that livestock magically generate fertility, that fertility is impossible without livestock.
So they think “I have to have livestock to do Permaculture, otherwise I have to import fertilizer.”
Here’s the most important fact to know: 100% of the fertility in any animal manure came from plants. Period. Animals originated 0 fertility or nutrients.
It’s a fact that livestock significantly REDUCE the net fertility produced by any system. Don’t believe me?
Here’s some numbers. According to the U of I a mature Holstein will require an acre of grazing under ideal pasture, but probably still need some imported feed. It will produce 210 lbs of total Nitrogen before leaching and losses. (I’ll focus on N since it’s the major limiting factor.)
Maintaining the pasture production will require 100-150lbs of N annually. If you’re grazing, there will be about 50% loss of N during the “cooling off” (even balanced manure like cow manure loses N as it sits) or storing phase, and probably another 20-40% loss after application to the garden.
Now, we have to fudge, because some of that “loss” goes to fertilize the pasture, and you had to import some feed, and the cow won’t always be mature…. So let’s say best case scenario you get 60lbs/year of N out of an acre of cow pasture.
So, to pick a heavy feeder and assume continuous cropping (so we have a steady annual comparison) let‘s use corn, which will require 200-240lbs+ lbs of added N for high average yields. (See link 2.) So, let’s just say our acre of cow pasture produces the fertilizer for 1/4 acre of corn, which is probably about right for good garden productivity.
Plus it will yield about 1 million calories of meat.
There are a few ways we can do non-livestock comparisons. One is to use Grow-Biointensive numbers, where by using carbon cropping on 60% of the garden area, a garden can reliably generate its own fertility without fallowing or cover cropping, if crop residues are returned in the form of compost. (Note that chop and drop would be even more efficient.)
So, one acre of diverse Biointensive garden will actually grow its own fertility, PLUS the fertility for nearly another whole acre.
Systems using this will necessarily increase in soil carbon over time without animals. And with carbon cropping on 60% of the land area (such as with corn) we’re likely to get at least 5 million calories out of that same acre, and get more net protein, too, and a far more diverse variety of nutrients. 4
Another way to do the comparison is raw N comparison. For example an acre of soy grown for fertility will have 240lbs of above ground harvestable N. 5. Plus fixation of about 100 lbs of below ground N, and it can be followed by a veg or calorie crop in the same season. Of course, there are technicalities as with manure as far as how much of that can be captured for a crop, but in any case it’s going to be far better than the 1/4 acre of fertility produced by the cow.
And for Permaculture, we have not even scratched the surface of ecosystem sources of fertility, such as wetland, forest, hedgerows, floodplain, slashmulch, Swidden, etc. which can provide fertility without livestock. Mollison emphasized all of these, such as with the hierarchy of soil creation, mountain top forest systems, etc.
So, for an area of intensive production, any land set aside for a cow will produce 1/4 of the calories and fertility as it could in a calorie crop garden.
But don’t livestock enrich the soil with microbial goodness? Not compared to compost! The compost process improves the quality of manure and composted plant material is better than manure. Holistic methods like mulching and using Polyculture probably work better for increasing microbial mass and diversity than livestock OR compost.
If you have too much land to manage without livestock, then by all means add livestock to he,p manage it. Or, if the land is no good for plant crops, by all means add livestock.
But the point is livestock are not needed for fertility and actually reduce net fertility compared to systems without livestock.
2: https://www.agry.purdue.edu/…/historical… (Continuing thoughts on animals and land use from my last post)
4. http://www.waldeneffect.org/…/Calories_per_acre_for…/5. http://bulletin.ipm.illinois.edu/?p=4773
(Picture: Alan Chadwick’s famous vegetable garden was extremely productive and grew its own fertility.)