This paper really picks apart the effects of juglone, its production levels, area of effect, and all the possibilities of growing crops under its influence. Written with permaculture in mind.
I especially like their recommendation to plant black alder (Alnus glutinosa) as a nurse crop between your rows of black walnut. Since they’re sensitive to the allelopaths, they die out. But in the meantime you’ve grown poles for coppicing, and leave a whole stump and root system to slowly release nitrogen to the walnut crop -an excellent example of systematic development by filling niches in time.