It's worth reviewing the Sow rules:
Caverna Rules, page 14 wrote:
You can grow crops with the “Sow” action. To sow Grain, take 1 Grain from your personal supply and put it on an empty Field. Then take 2 Grain from the general supply and put them on top of your sown Grain.
Instead of Grain, you may sow Vegetables. Take 1 Vegetable from your personal supply and put it on an empty Field. Then put 1 Vegetable from the general supply on top of your sown Vegetable.
With a single “Sow” action, you can sow Grain and Vegetables up to 2 times each.
To sow, you take 1 Grain or 1 Vegetable from your personal supply. If you don't have one, you can't sow.
And it's only 1, not 2. The sow action may let you sow multiple times, but it's one item from your supply each time.
To sow, you put the item on an empty Field. After that, the field is no longer empty. Even if you can sow again right away, you can't do it on that Field.