First, let’s consider the supposed necessity of using manure. The agroindustry clearly shows that it’s possible to grow food without any manure. Food is produced using chemicals for fertilization, or even without soil by using liquid feeds in hydroponic culture. At the other end of the spectrum, if we look at a natural system such as a forest, plants grow wonderfully without the addition of manure.
Farmed-animal manure is not necessary for crop production. Organic farms have access to such large amounts of manure because the high consumption of animal products in North America results in an abundance of animal feces. Manure used in organic food production is often sourced from animals that were raised in inhumane conditions and exposed to contaminants like pesticides, antibiotics, and GMO’s. This excess of manure is a modern condition, resulting from densely-packed industrialized farms and a dietary shift in westernized countries to animal-centered meals, but manure is by no means the most efficient or cleanly-sourced way to fertilize organic crops.
In fact, it would be more efficient to directly use the fodder to fertilize the soil than to feed the animals, collect the manure, compost it, transport it, and spread it on the soil. And by using plant-based fertilizers instead of manure, farmers can produce fertility from their own land and use fertilizers that have not been exposed to common agricultural contaminants.
Instead of adding manure to the soil, we can add plant-based fertilizers like mulch, “green” manure, vegetable compost, and chipped branch wood. This provides food for the multitude of organisms that live within the soil. The organic material is decomposed and eaten by earthworms, arthropods, fungus, and bacteria, making nutrients available for the plants. In other words, “manure” is present, but it comes naturally as a byproduct of this free living fauna.