We don’t need more farm laborers. That’s a con job promoted by cheap labor profiteering agribusiness. In fact, given the ongoing mechanization of agriculture, we’ll be lucky to have enough jobs for people who are already here.
One of the unintended consequences of Mexican 'cheap labor' is once they become citizens they quit 'picking' and move to the bottom of the blue collar ladder. Since they're hard working - they move up the ladder - - taking higher paying jobs from Americans.
So, "no" those 'already here' won't be going back to the fields.
The 'illegals' system was constructed so every few years a whole new group of illegals had to be brought in... horrible incentives.