Good points Emilie.
I would like to add that make sure that fertilized crops have greatly more yield than non fertilized crops, for 2 reasons.
1)Makes sense
2)At the current ratios (and even planned ones) if it takes 1 seed to yield 5 crops unfertilized, 1 seed + 1-2 guts/fish to yield 10, then no point in fertilizing when you can simply just plant another one. Fertilizing to 100% should give about 3x more yield (3 for unfertilized, 8 to 10 fertilized).
Also note that farming is 100% upfront cost. Land usage area, 4 fertilizers, 1 water, 1 seed. If you do not properly farm/harvest it correctly you are out all those resources.
Yield should be effected by skill. Allow the best farmers to want to plant/harvest. Let the trainees and workers learn skill by tending the fields, which have no effects on failures but only when the work is done. Allowing new players, and helpers to help with farming without messing up the crop size.
A large worry is that if you are low skill you will not get food, well farming at low levels will yield still a LARGE harvest IF you use fertilizer and it has the effect as noted 3x. But I think it makes sense this way while still allowing low skill helpers to get skill through farming without messing up the crops for skilled farmers.
I think getting more than 1 seed from extracting makes sense also (should be done for forestry also IMO) however, I think more than 5 is a bit over kill. You can base this on skill.