Lots of things, like fruit, you can harvest once, then go back a week later and harvest some more.
I think that the rule was to harvest once, then open it to gleaners. Or, in the case of something like a grain field, don't harvest too carefully. Leave some in the corners. Or let some fall as you go.
Interestingly, you were NOT instructed to harvest and deliver it. SOMEthing was left for poor folks to do on their own behalf.
Something which the lecture doesn't emphasize, but which he does emphasize elsewhere, is that long lived cultures burn wood for heating and cooking, then mix the ashes into their gardens for the minerals. Also, they appear to "cut" their salt with it, for direct mineralization. Pretty interesting.