Fertilizer run off from organic farms contains just as many nitrates as metal^h^h^h^h^h^h non-organic farms. Those are the pollutants that cause the biggest problems in water ways and generally encourage algal blooms that kill other plants and animals.

Switching to plant based agriculture would require even more fertilizer to be used as the land area needed limits super effective crop rotation.

Other problems are plants are much less tolerant of different environments than live stock, so you have to more aggressively farm the limited area. Many of the ideal areas for growing plants also lack nutrients or even water (CA is essentially a desert but grows most of the worlds cereals because the weather, soil are excellent for growing, even if you have to pump the water in from elsewhere...)

Of course this ignores harmful effects of livestock, and is just meant to illustrate “not livestock” does not mean “good”.

Just wanted to add some supplemental material.

A few write-ups with accompanying audio transcripts/podcasts from science writer Brian Dunning of Skeptoid.

- Organic vs. Conventional Agriculture: https://skeptoid.com/episodes/4166

- Organic Food Myths: https://skeptoid.com/episodes/4019

- Environmental Working Group and the Dirty Dozen: https://skeptoid.com/episodes/4623

Bibliographic references and further reading at the end of each if interested.

It depends a lot on the crops and the actual production methods, but from talking to my neighbors at the post office, in organics, sometimes more land is consumed (since production per unit area can be lower) and soil erosion is higher (you cannot no-till without herbicides.) I am not very well versed in this but simply wanted to point out that our assumptions may not be correct.

As for traditional production, herbicides, pesticides, and genetic contamination are big issues.