The Vegetable Field works on a 5 day cycle:
Day 1 : Growing (nothing needs doing)
Day 2 : Growing (nothing needs doing)
Day 3 : Growing (nothing needs doing)
Day 4 : Growing (nothing needs doing)
Day 5 : Pick your vegetables (work is intelligence related)
If you employ your workers at 0 stats, you will normally get 4 vegetables.
If you employ your workers at 20 stats, you will normally get 4 vegetables (the maths works it out to be 4.4, which is rounded down to 4)
As you can see, you would normally only hire workers at 0 stats.
The average price for vegetables is around 11 pounds. The maths is:
(4x11)-16=28 pounds
This averages out to 6 (5.6) pounds per day.
If this is your second field, there is a -25% penalty imposed on your yield. So the numbers for a second field look like this:
If you employ your workers at 0 stats, you will normally get 3 vegetables.
If you employ your workers at 20 stats, you will normally get 3 vegetables (the maths works it out to be 3.3, which is rounded down to 3)
0 stats : (3x11)-16=17 pounds profit.
Which averages out to 3 (3.4) pounds per day.