How is it possible

This past week my husband spoke on the Harvest and how the Land in Israel was supposed to be handled. The farmers where to farm for 6 years but the 7thyear would be the sabbath. This passage had me scratching my head, because part of it said G-d would provide enough harvest in the six year that they wouldn’t need to work the field. What I didn’t understand or maybe connect is that G-d said they could pick some of the food. Picking isn’t the same as harvesting where, they’d be sowing seed, pruning and other activities requiring the field to work, picking would be like taking fruit off a raspberry bush in the wild.
My question was how would they have preserved their food because well lets face it we still can’t preserve many things for more then 1 to 2 years, and at the 3 years point, I can’t think of anything still edible. So my question was what were they doing that we have lost over the thousands of years since that time. I have found when reading the old Testament G-d says the same thing and sometimes when it repeated it a little confusing because you have to go back and reread the first time. Maybe G-d was trying to make it clear to his people what was expected and how to follow his rule. I wonder if annuity explanations would be easier to understand then some of the Word of G-d.