Home / H. Environment, ecology and agriculture / Part IND
"Agriculture can't work without manure."
agriculture works with green manure, composting, crop rotation with legumes, which fix nitrogen in the soil, and mineral fertilizers. Besides, manure comes from animals fed on crops: it returns to the soil part of the nutrients that were taken out to grow their feed. Without animals, far less land would be needed, and nutrients could go straight from plants back to the soil.
Short answer
Agriculture has many ways to fertilize: green manure with legumes, which fix nitrogen from the air into the soil, composting plant waste, crop rotation and mineral fertilizers. Manure doesn't create nutrients: it returns to the soil part of what the animals ate, and those animals eat crops. Without livestock, far less land would be needed, and nutrients could go straight from plants back to the soil.
For children
Plants need food to grow, which comes from the soil. Manure helps, but it isn't the only way. You can make fertilizer from plant scraps, leaves and peels, and grow beans and other plants that make the soil stronger. That way, plants grow well without needing animals.
"If manure comes from animals that eat crops, where do the nutrients in manure come from?"
Como pode aparecer
"Without animals there is no fertilizer."
"Organic farming depends on cattle."
"Your organic vegetables were fertilized with manure."
"Vegans eat plants fertilized with cow dung."
"Crop-livestock integration is essential for soil fertility."
"Cattle graze where crops can't grow." (which is H4)
The strongest version
"Without animals there is no fertilizer. Organic farming depends on cattle."
Strongest version (steelman):
- P1Plants need nutrients such as nitrogen, phosphorus and potassium.
- P2Animal manure is a traditional source of these nutrients, especially in organic farming.
- P3Without animals, there wouldn't be enough manure.
- CSo agriculture depends on raising animals.
P1 and P2 are true. The problem lies in P3 and the conclusion: there are other sources of nutrients, and manure doesn't create nutrients, it only returns part of what the animals ate.
The argument is valid. Its soundness fails because it ignores the alternatives and where the nutrients in manure come from.
Full answer
- a
Reconstruction and diagnosis
The argument treats manure as a source of nutrients, when it's a middleman:
Step What happens Feed crop Takes nutrients out of the soil The animal eats the feed Uses part of the nutrients; the rest becomes manure Manure returns to the soil Returns part of what was taken out Without the animals, plant residues could go back to the soil directly.
- b
Where the argument breaks
1. Manure is a middleman.
It returns to the soil nutrients that came from the plants the animals ate, with losses along the way.
2. There are well-known alternatives.
Green manure, composting, rotation with legumes, cover crops and mineral fertilizers are established farming practices.
3. Legumes fix nitrogen.
Beans, soy, peas and other legumes host bacteria that capture nitrogen from the air and leave it in the soil.
4. Without livestock, far less land would be needed.
A global vegan diet would reduce farmland by about 75%. Less cropland means less need for fertilizer.
5. Vegan farming exists.
There are growers who farm without animal inputs, sometimes called "veganic", and even a certification for it, the Biocyclic Vegan standard, used mainly in Europe.
- c
Data and sources
Source What it says Note Our World in Data, land use and diets A global vegan diet would reduce farmland by about 75% Based on Poore and Nemecek, 2018 Embrapa, green manure as a source of nitrogen (in Portuguese) Legumes fix nitrogen in the soil; green manure and composting replenish organic matter A publication by Embrapa, Brazil's agricultural research agency - d
The strongest counter-reply: manure is a useful byproduct
The most serious version grants that there are alternatives, but says that as long as there are animals, using their manure is better than wasting it.
- e
Why the counter-reply doesn't reach the conclusion
Using it doesn't justify producing it.
That manure is useful isn't a reason to raise animals.
Excess manure is a problem.
In regions of intensive livestock farming, manure pollutes rivers and soils.
The transition can be gradual.
Agriculture can reduce its dependence on manure as livestock farming declines.
- f
Back to the moral question
Agriculture doesn't depend on raising animals to kill them. If there are ways to fertilize without them, the argument doesn't justify livestock farming, and the moral question returns to the center.
Reasoning errors
Logical
Is the form valid?
False dichotomy
Epistemological
Does the evidence support it?
Not knowing agronomy
Reversing the origin
Biases
Extrapolations
The principle being tested is: "if a byproduct is useful, the activity that generates it is necessary".
If it applied to…Ash from burned forestsTap to see
Burning forests would be necessary for fertilizer
No one concludes this
If it applied to…Heat from coal plantsTap to see
The plants would be necessary for heating
No one concludes this
If it applied to…ManureTap to see
Livestock farming would be necessary for fertilizer
There are alternatives
Contradictions
Most conventional farming uses mineral fertilizer.
Which also needs fertilizer.
The criterion only comes up against vegans.
What the argument gets right
What is true
Manure is indeed a traditional and useful fertilizer, and integrating animals and crops has a long history. A transition to systems without animals requires knowledge and investment, and doesn't happen all at once.
But
But agriculture doesn't depend on animals. Plants can feed the soil directly, and without livestock, far less land would be needed to feed the world.
Connections
Usually comes before
Usually comes after