Frozen soil for the last week has put a halt to lifting tubers, but the last plant I lifted from semi-frozen ground came up so cleanly that the root system was almost intact. This gave a really good view of the root extension and structure.
Notice the original planting tuber, which is still firm and unrotted. I've always thrown these aside (they do not look appetizing) as I would when lifting potatoes, but I'm curious to see if they resprout in Spring, and perhaps take advantage of that existing root system to get a flying start. Looks like something else for me to try this coming season. If anyone out there has tried it, I'd love to know. (update 1/3/10, The original tubers, which I temporarily heeled in with a view to replanting, have in fact now rotted. Some sources state that oca is a perenial, others an annual. My observations would sugest that Oca is not a true perennial, but a plant-replant annual. End update)
When thinking about intercropping, it's simple enough to see if crops are competing above ground, but this got me searching out my well thumbed copy of Robert Kouriks classic read Designing & Maintaining Your Edible Landscape Naturally which contains some eye-opening scale drawings of various vegetable root zones in the section 'Intercropping Below Ground - The Shape of Roots', which are helpful when visualising the amount of competition between plant root systems. From observation of the plants I've lifted, Oca roots seem to have a similar range to tomatoes - 3 feet radius by 4 feet deep, but with most of the fibrous rootball close to the planting tuber. The fleshy roots, one of which grows from each eye, extend further and send out a more sparse network of fine root hairs which are difficult to follow in the soil, so it's hard to say exactly how far they spread.
But most importantly - those fleshy root stems are STILL alive despite the devastation to the plant above ground caused by days of continuous sub-zero temperatures. My hunch is that tubers continue to expand even this late, by drawing sap from these root stems.The experiment here will hopefully confirm this.