How long after you cut down a walnut tree is the soil soured from it? I have cut the tree down appoximately 4 years ago is there anything to put on the soil to reestablish my garden. The vegetable plants are stunned and very yellow leaves before they mature and bear fruit.
The short answer would be a long time, years before the toxic chemical known as juglone would be depleted, at a variable rate according to the makeup of your soil, but years as you already know. Healthy well drained soil with a fair amount of organic matter supports microbial activity that actually feeds on juglone. Substantial root material is often left in the soil however, which would be juglone laden and would take a long time to decompose. Even at total decomposition of the root material, juglone could still be present in the soil. Other possibilities....raised beds could work but could also compound the problem. Moving the vegetable bed to another location would work. Growing vegetables in containers also works.
Best idea if moving isn't possible, would be to have a soil test done from the root zone of your projected vegetable plants. http://msusoiltest.com/
Tell them what you want to grow in the soil and they will analyze and make specific recommendations. Even if the garden site could be moved, a soil test would still be recommended. There is no other way to know soil makeup/nutrient levels without a soil test.
Otherwise here is a comprehensive link to more on black walnut allelopathy.