It can only make sense to make use of "nature's plough". If you leave a pig destroyed patch of ground for a while it'll end up full of weeds, the pigs having brought all the dormant seeds up and let them germinate. We harrow, leave for a little while to let any docks etc stick their heads above ground, spray them off, wait till they've died back then broadcast seed and harrow again to try and hide the seed from the birds. What to sow is up to you. We've just sown a patch of winter wheat to see how it goes. In the spring we'll be sowing fodder crops such as beet or kale.