I did a test yesterday to compare the small, medium, and large crop plots by building one of each right next to each other, irrigating them via pipes, putting one sack of fertilizer in each, and seeding them with a narcoberry seed.
So far, they've started fruiting, and they're all at 3 narcoberries. Same spoiling time, same growth rate. The only three differences are (1) larger crop plots take significantly more resources to build, (2) larger crop plots are harder to place because they take up up to 4x more ground area (large vs small), and (3) each crop plot has 200 more water capacity than the previous one, which is entirely useless unless you don't plan on irrigating them, and instead waiting for rains to come.
So, in conclusion, the engram points and effort required to build large versus small crop plots is completely not worth it at the given time. Hopefully the devs will take a look at this.
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Edit 1
Narcoberries spawn a maximum of 30 berries at the same growth rate using the same amount of fertilizer for every size plot.
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Edit 2
Medium and large plots growing savoroot are exactly the same. Caps at 13, same growth rate.
Large crop plots are useless.