First you should clear all the weeds and place fertilizer on the soil to make weeds not appear again
So you will need:
1. A bot who harvests the crops
2. A bot who collets the crops
3. A bot who makes seeds
4. A bot who plants seeds
(That is what i have but you can have 3 bots with 1 making seeds and planting them but i think that would be worse)
Also you make seeds in a Cereal Seeder (1 cereal = 2 seeds)