potato harvest time

Got my first chance to dig potatoes yesterday
i think that's where the term 'back breaking work' comes from
the constant bending over to pick up the potatoes is tiring
but it was nice to be out in the sun and wind working and being productive
I only worked for about 4 hours.
got about 50kg of potatoes
I got a lot of chaff for mentioning that potatoes came from South America
they then started listing off all the things that people from the Ukrainian part of the USSR invented or created.

Why do farmers burn their fields?
It seems so wasteful
can somebody explain?
It was one of my jobs yesterday to clear the field of all the previously mowed fallow and pile it up so that it could be burned. I don't understand. They need more nitrogen?

I noticed that many families hire a tractor to turn the field and then just go pick up the potatoes
I was glad that I got to do the actual hoeing, but even more glad that I don't have to bend over that many times every day
time for my bus...
josef