Complex sentence: It is best to only sweep a few rows ahead of the harvesters at any given time, to prevent the tractor that drives the harvester from crushing the nuts that may still be falling from the trees.
Split into simpler sentences: It is best to only sweep a few rows ahead of the harvesters at any given time. The reason for this is to prevent the tractor that drives the harvester from crushing the nuts that may still be falling from the trees.