The Polyformer is a 3D printer filament extruder created for people living in 3rd world countries with limited access to affordable filament. It allows you to recycle PET plastic from beverage containers by cutting them into a ribbon and feeding the ribbon through a heated extrusion nozzle.
Not everything is irrigated. They showed areas that are only fed by rainwater.
I think the point is that the soil was swept away and the ground is impermeable so any rainwater flows into the river or evaporates rather than supporting plant life or replenishing the groundwater.