Manure and feed conversion ratio

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Canastenard
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Manure and feed conversion ratio

Post by Canastenard »

As vegans one of the most common arguments we tend to tell is that feed conversion ratio from animals is poor, and that it takes many times a given amount of calories from plants to have the same amount of animal product calories. However, a considerable part of that loss comes in the form of feces and urine, which can be used as fertilizer in the form of manure. So technically a part of that lost energy is actually reused to fertilize other crops.

Now I'm not saying that the argument is invalid, as other energy is lost outside of feces and urine (for example, heat loss and unedible part of the carcass) and manure comes with its own set of problems as well (like methane emissions and potential pathogens). The question I'm asking is not about a whether the argument is valid but rather a question of to which degree, so we can be more honest when we argue.
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Jebus
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Re: Manure and feed conversion ratio

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This doesn't affect the argument that more land is required to produce a certain amount of beef compared to the same amount of grain. I try not to use specific numbers when using this argument as I don't want the whole point to be debunked just because I got the numbers wrong. What you are pointing out could be used in the plus (pro beef) column just like methane gas production could be used in the minus column even though neither of these points affect the original land requirement claim.
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Canastenard
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Re: Manure and feed conversion ratio

Post by Canastenard »

Yeah of course I'm not arguing that using more land to feed farmed animals then using their poop as fertilizer to plant-based food that's mostly going back to farmed animals is a good idea. It's just that the numbers I'm familiar with are generally a 10% feed conversion ratio from plant food to beef and that because of manure fertilizer maybe it's lower than that. Unless that number is already taking this variable into account?

If anyone who has a better idea about this give a new approximation taking manure into account (if it's not already the case) it would make the argument more solid when giving a specific number, but I understand your point about not giving one to not have your argument discredited because of one error. But having one would still be interesting if people ask.
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brimstoneSalad
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Re: Manure and feed conversion ratio

Post by brimstoneSalad »

Manure is not food, and fertilizer can be produced synthetically so it doesn't detract from our food production.

If you wanted to, though, you could look at manure output and compare that to how much land it would take to produce that much green manure.

That said, we probably need to start making better use of materials recovered from human waste streams.
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Canastenard
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Re: Manure and feed conversion ratio

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Yeah of course manure isn't food, I'm saying that since part of the energy wasted in animal agriculture becomes manure, which can go back to plant agriculture, then that part of the energy isn't completely wasted. And I know there are synthetic fertilizer, but these cost energy to be made and while we have animal agriculture the energy used by producing synthetic fertilizers can be reduced by replacing part of it with manure. But of course the combination of manure + animal food is not going to increase the amount of edible calories compared to eating plants directly, "animal manure is necessary for agriculture" is not my point.

My point is that since a part of the wasted calories in the form of animal urine and feces can actually be reused to fertilize crops, then part of the calories wasted actually comes back to food. Variables to calculate that would be how much energy loss from animal agriculture comes in the form of manure that can be reused to fertilize crops, how much of this energy from manure is used by plants to grow, and finally whether those plants are fed directly to humans or fed back to farmed animals.

Also there's something I'm wondering about: how do we get nutrients from nature to agricultural lands in a sustainable way? Even with perfect optimization of agricultural, food and human waste I think we're never going to fully close the cycle which is going to have some loss at every revolution, so we'll always need to take some nutrients from nature. We should also limit land use as naturally growing forests are probably better for carbon sequestration than any human-made agricultural system, and less land use also means less disruption of wildlife. Of course nutrients can be mined but that doesn't seem sustainable due to the fact we extract them faster than their reserves can be restored.

Maybe we could make some areas destinated to growing green manure, that would be somewhere in between nature and agriculture, and would basically be transition areas between the former and the later: they wouldn't need as much human inputs as agricultural lands and because they're not overexploited they would fertilize themselves better than, say, a land exclusively used for wheat, but part of their organic matter would be taken to be used as green manure to fertilize agricultural lands, and then we leave them alone for some time before taking organic matter again (we don't want to take too much, it must recover otherwise we're breaking the "not overexploited" point). Preferably they would be forests because trees are great carbon sinks, and if regulated properly, they maybe wouldn't be much worse for the environment and wildlife compared to nature that's completely left alone. Technically that would still be increased land use for our agricultural ends, but it wouldn't be like a farm that decreases environmental damage by acre of land but uses more land for the same yield, resulting in a net negative for the environment compared to something more conventional, since contrary to that what I'm proposing here it wouldn't use land homogeneously (one part to grow crops for humans that must take as little land as possible without compromizing sustainability and the other part for green manure being closer to nature). And of course the lower the need for it the easier it is to harvest it sustainably, as we should let nature restore biomass in these areas, so we should lower the need for it by doing other efforts like limiting losses at each revolution of the agricultural cycle and preverving the fertility of soils where we grow our crops like wheat and soy for example with little- or no-till farming, and I'm not opposed to artificial fertilizers if sustainably harvested green manure isn't enough.

Does that make sense or it is irrealistic? It doesn't sound like pseudoscience at least? Or does it? I'm only making an hypothesis based on my limited understanding of agronomy and ecology, so I'd like to see my hypothesis criticized or even refuted if necessary, by someone with better knowledge than me in that regard.
Last edited by Canastenard on Tue Oct 17, 2017 3:23 pm, edited 2 times in total.
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brimstoneSalad
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Re: Manure and feed conversion ratio

Post by brimstoneSalad »

Synthetic ammonia is produced from natural gas, which is not otherwise very important for producing food. If the question is simply feeding the world today with no concern for long term environmental impact (global warming), then synthetic nitrogen production doesn't take from available food. It doesn't require significant land use, etc. it only has a resource cost, but a resource that is currently plentiful and not a limiting factor.

When we're asking environmental questions of total greenhouse gas output, that's another issue.

For that, we would be interested in things like green manure and intercropping. We might be looking at using something like 2x the land to do that, to grow enough green manure to sustain cereal crops.

http://www1.agric.gov.ab.ca/$department/deptdocs.nsf/all/agdex133
For example, a cereal crop requires 45 lb/acre of nitrogen for optimum growth. The cereal crop can obtain 12.5 lb/ac of nitrogen from the ploughed-down legume crop if the legume residue contains 62 lbs/acre of nitrogen. Assuming an additional 9 lbs/acre of mineral nitrogen is released from the soil reserves, then the cereal crop will require only 23.5 lbs/acre of fertilizer nitrogen. In most cases, as in this example, legume green manuring does not supply all the nitrogen for optimum crop growth but can reduce the amount of nitrogen fertilizer required.


That's a speculative example from crop rotation.

It's very likely that just by eating more legumes (as a higher ratio of diet than grains, which vegans should be doing for protein in replacement of meat anyway) there would be enough nitrogen fixation for the cereal crops we eat, particularly if we can do waste stream recovery ( https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5274620/ ) which is really the priority here when it comes to closing the loop (animals certainly don't help).
Canastenard wrote: Tue Oct 17, 2017 11:35 am Variables to calculate that would be how much energy loss from animal agriculture comes in the form of manure that can be reused to fertilize crops, how much of this energy from manure is used by plants to grow, and finally whether those plants are fed directly to humans or fed back to farmed animals.
Fungus can use the energy in manure to grow, but plants do not (beyond possibly saving the trouble to fix as much nitrogen for nitrogen fixing plants). Nitrogen just makes them grow faster because it's a limiting factor. They only use the minerals (mostly phosphorous, which can also be provided as ground up rock or other sources, or by better farming methods) and the fixed nitrogen.

Plants need something like 50 lb or nitrogen per acre, which equates to thousands of gallons of liquid manure (something like 4,000).

We can compare the nitrogen in manure to synthetic and look at the energy savings, but they're still not 100% identical.
Canastenard wrote: Tue Oct 17, 2017 11:35 amAlso there's something I'm wondering about: how do we get nutrients from nature to agricultural lands in a sustainable way?
We need to recover nutrients from the human waste stream. We don't have to completely close the cycle, we do get some nitrogen fixing from legumes we already grow, and we get phosphorous and potassium and other minerals from the soil (particularly from trees with their deep roots), alley cropping is a way to take advantage of deep rooted plants pulling these minerals up.
Canastenard wrote: Tue Oct 17, 2017 11:35 amOf course nutrients can be mined but that doesn't seem sustainable due to the fact we extract them faster than their reserves can be restored.
Doesn't really matter, most of the earth's crust is made of these things. The only reserves that are running out in any meaningful way is the most concentrated forms which are the cheapest to mine, transport, and spread on fields. There's still a virtually unlimited quantity, it'll just cost a little more.
Of course we should recover these thing from the waste stream, and will as soon as it costs less than mining it fresh.
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