Where to find root structure information for intercropping purposes

One of the goals of intercropping that I often read about, but struggle to implement, is the mixing of plants that occupy different root zones, for example planting shallow rooted plants near tap rooted ones. I would like to do more to take advantage of this, but sometimes I have difficulty finding useful information about a plant's root structure. The root structure descriptions, if I can find them at all, are often a vague binary, when in fact there is a spectrum between deep rooting and surface rooting. I certainly have no interest in digging up my existing perennials to discover the nuance.

Is there a resource that has reliable information on the root structures of perennial food plants? I would be surprised if a permaculture author hadn't made some kind of root zone compatibility table to use as a reference. I would be grateful for any information you can provide.

Here ya go: Understanding Roots, by Robert Kourik

...Understanding Roots contains over 115 enchanting and revealing root drawings that most people have never seen, from prairies, grasslands, and deserts, as well as drawings based on excavations of vegetable, fruit, nut, and ornamental tree roots. Every root system presented in this book was drawn by people literally working in the trenches, sketching the roots where they grew.

The text provides a verydetailed review of all aspects of transplanting; describes how roots work their magic to improve soil nutrients; investigates the hidden life of soil microbes and their mysterious relationship to roots; explores the question of whether deep roots really gather more unique nutrients than shallow roots; shares the latest research about the mysteries of mycorrhizal (good fungal) association; shows you exactly where to put your fertilizer, compost, water, and mulch to help plants flourish; tells you why gray water increases crop yields more than fresh water; and, most importantly, reveals the science behind all the above (with citations for each scientific paper)...

Description from Goodreads, here.

Oh, and welcome to Permies!

Joylynn Hardesty wrote:Here ya go: Understanding Roots, by Robert Kourik

...Understanding Roots contains over 115 enchanting and revealing root drawings that most people have never seen, from prairies, grasslands, and deserts, as well as drawings based on excavations of vegetable, fruit, nut, and ornamental tree roots. Every root system presented in this book was drawn by people literally working in the trenches, sketching the roots where they grew.

The text provides a verydetailed review of all aspects of transplanting; describes how roots work their magic to improve soil nutrients; investigates the hidden life of soil microbes and their mysterious relationship to roots; explores the question of whether deep roots really gather more unique nutrients than shallow roots; shares the latest research about the mysteries of mycorrhizal (good fungal) association; shows you exactly where to put your fertilizer, compost, water, and mulch to help plants flourish; tells you why gray water increases crop yields more than fresh water; and, most importantly, reveals the science behind all the above (with citations for each scientific paper)...

Description from Goodreads, here.

Oh, and welcome to Permies!

WOW I was not expecting such a perfect response! Thank you! This is exactly what I was looking for.

The shorthand rule that Dr. Christine Jones suggests (for pasture, but it's what I like using in general, so I don't have to remember just everything) is to plant members of at least four 'functional groups' (grasses, legumes, tall herbs, short herb) which generally equates to 4-8 families within the shared root zone. (Though I think Joylynn just sold me a book, too!)

Christopher Weeks wrote:The shorthand rule that Dr. Christine Jones suggests (for pasture, but it's what I like using in general, so I don't have to remember just everything) is to plant members of at least four 'functional groups' (grasses, legumes, tall herbs, short herb) which generally equates to 4-8 families within the shared root zone. (Though I think Joylynn just sold me a book, too!)

I've seen this advice, and it makes sense to me except for the grasses. I've never tried intercropping grasses but it seems like it might be troublesome. Grasses can be very aggressive weeds and readily drop seeds during harvest. Self-seeding is fine for  vegetables and (to some extent) pulses, but I don't think I'd want to have my wheat/quinoa/amaranth/buckwheat harvest spread out over a large area. I have not yet grown any grains, but harvesting them (finding the right ripeness, and then stacking them into shocks etc.) seems finicky enough without having to run around my garden collecting 5-10 stems at a time. That is my very amateur impression, however I would be grateful to be corrected.

I mostly think you're right. That's an example of where it's really a guide for pasture management. On the other hand, corn is a grass!