Yes, but the problem is that meat consumes approximately 25 plant calories to produce 1 meat calorie. It's a reducing function, which means calorie for calorie meat produces 25 times as much greenhouse gas simply from the costs involved in plant production.

This isn't universally true - some meat is grown by grazing "free" plant calories. But it is true for grain fed cattle -- for most US industrial meat production.

The methane production issue is in addition to the plant/meat production inefficiencies.

Fortunately, there are other means of fertilising. Green manures - generally annual legumes - are a good option. The difficulty is that this, and other organic approaches to fertilising and structuring soil, require a proportion of land to be allowed to lie fallow for a while.

In other words, fertilising the soil with fossil fuel derived products is just.. more profitable.

The solution is probably carbon pricing of some kind for fertilisers: the cost of organic farming needs to be roughly the same. Agricultural subsidies are already enormous, so some of them could be directed to food prices directly, to ease the transition for consumers.

This is unrelated to the argument that animal feed from plants is/isn't a sustainable method of carbon capture.

That isn't true. The carrying capacity of the earth would shrink but there would be enough food for at least a billion people.

This is true, but if you use synthetic fertilizer, even if the fertilizer itself contains no carbon it still uses hydrogen split from methane. The carbon part has already gone into the atmosphere, which plants then pull down. You would need to sequester the carbon released during SMR for synthetic fertilizer to have no effect.