Eh, I've started growing exotic fruit trees for a few years now and never measured any of the elements in the soil whatsoever and just periodically add more fertilizers into the soil- So far my Cherimoyas have been fine.

The only thing that ever kills off any of my plants is winter, specifically this last one killed off a few of my starfruit, despite me taking them in every night for months on end- we had one of the harshest winters in something like 40 years here, so not much I could do about that...

Potatoes definitely are one of the easiest things to grow ever though- like I'm growing them too and my grandfather got the mower out to cut the grass and accidentally ran them over on 3 separate occasions- and everytime the potatoes grew back perfectly fine like they didn't even notice.

Anyways, the question anon asked was if it was profitable to grow potatoes- and sure it can be, if you have a massive amount of land and a large cheap labour force- or super expensive advanced farming equipment to plant and harvest them. Potatoes are extremely cheap and to become rich farming them you'd need to produce hundreds if not thousands of tons of them- which would require a ton of work to plant and harvest them & a large amount of starting land.

In contrast, lets say you have 1 acre (43560ft)- According to a starfruit growing guide 1 Acre would be adequate enough to support 2,178 Star fruit trees. A 3 LBS package of Starfruit on amazon is 80$, A single Starfruit tree can produce 200~400 pounds of fruit per year. To make it more even, we'll go for the 300 Lbs of fruit per tree- 2,178 x 300 = 653,400Lbs of fruit, @ 80$ per 3 Lbs = 17,424,000$

Meanwhile, Walmart is selling a 10Lbs bag of Potatoes for 6.88$, which is 68.8 cents per pound- and according to a potato farmer in Oregon they produce about 22,000 Lbs of potatoes per acre per year. 22,000 Lbs @ 6.88$ per 10 Lbs = 15,136$

As you can see, the profits from potatoes is far far far less than profits from growing exotic fruit- however this usually means you must live or operate your farm in warm tropical climates, meanwhile potatoes will usually grow literally anywhere. Another bonus for fruit trees is how much easier it is to harvest, digging up and harvesting potatoes is a massive chore unless you have expensive farming equipment, plus you need to re-plant them after every harvest while a fruit tree will continue producing for decades if not a whole lifetime after they are established.