This seems like an impossible requirement to meet for landlocked countries.

I didn't see how deep they go here: for example, Ireland ranked higher than I expected, because of a lot of dairy and meat production. But how much of the cattle feed is imported?

According to this article, "Ireland imports around 80 percent of its animal feed, food, beverages, and other agri-food products".

https://en.wikipedia.org/wiki/Agriculture_in_Ireland

I haven't examined the source link to see if that's fully accurate, but if it's even mostly true, and that import collapsed, it would be a catastrophe.

It's not enough just to label a country as producer/not producer for a category but rather whether that production is fully stable and internalized in case of disasters/war.

My guess is that the results in the study should look worse for many of the countries listed.