Please explain how the Israelites were supposed to keep the Sabbath year

Leviticus chapter 25 describes a "Sabbath year" for the land. Every seventh year the Israelites were not supposed to prune their vines nor plow or plant their fields. > Lev 25:3-7 (NET) (Lev 25:3) Six years you may sow your field, and six > years you may prune your vineyard and gather the produce, (Lev 25:4) > but in the seventh year the land must have a Sabbath of complete rest > – a Sabbath to the LORD. You must not sow your field or prune your > vineyard. (Lev 25:5) You must not gather in the aftergrowth of your > harvest and you must not pick the grapes of your unpruned vines; the > land must have a year of complete rest. (Lev 25:6) You may have the > Sabbath produce of the land to eat – you, your male servant, your > female servant, your hired worker, the resident foreigner who stays > with you, (Lev 25:7) your cattle, and the wild animals that are in > your land – all its produce will be for you to eat. Apparently the Jubilee year is every seventh Sabbath year, but has additional features. If I have misunderstood the text (I think the 49th year counts consecutively and the 50th counts inclusively so they come out the same) please let me know that too. The text does say they could eat the "Sabbath produce", I assume that was whatever grew by itself from the prior year's planting, yet it specifically excludes any grapes. God does say, in verses 19 to 22, that He will increase the harvest of the sixth year. I wonder how practical this is, and to what extent a miraculous harvest would be needed to provide enough to sow the land and eat through the eighth year. Is there anything in the Bible or history or tradition that would explain this better?