Sunday, 6 December 2009

Tubers - Big and Few, or Small and Many?

Fruit thinning works for gooseberries, could it work for Oca?

(Above) 6th December, a mass of stem-rooting tubers forming above ground.

Oca tubers form close to the roots of the plant, but also where stems come in contact with the soil - up to several feet away from the original planting location. Seeing this mass of small tubers today reminded me that last year, although the total yield (weight) was fine, a high proportion of the tubers were too small to be worth cleaning and cooking.

So how to maximise the proportion of large tubers?
Remove some exposed tubers while small, so that the plant's reserves are concentrated into those remaining?

Prevent stem-rooting (by keeping stems from contacting the soil) so that only the tubers associated with the original roots form, giving fewer, larger, less dispersed tubers ?

Either of these approaches would detract from one of the crop's great plus-points - it is zero-work. Others have grown Oca in containers, which might limit the stem rooting tubers, but I have not heard reports of larger tubers from this method.

I'll let the crop run it's course this year, but this is something to ponder, and maybe test out next year.

UPDATE. An example of training Oca to grow upright (using canes) here: Thriftyliving

Wednesday, 2 December 2009

Oh-oh! Oca allelopathy!

Is Oca Allelopathic?

Allelopathy is the ability of a plant to chemically suppress the growth of another.
I've just discovered the excellent Radix blog, which focuses on unusual root crops, and it strongly suggest that dried Oca foliage inhibits germination (of lettuce seed in the experiment).
This obviously is important when mixing and overlapping crops.

But it may not be all bad news. Managed carefully, decaying Oca foliage debris could be beneficial in ensuring a weed-free bed for any following crop, as is the case with several traditional green-manure crops. The real problem would be if the plants roots exuded suppressive chemicals while growing. This would make it highly unsuitable for bi-cropping. So far I have seen no evidence of this, but I will be watching out for it.

What I need to do is an experiment to test for this next growing season. Hmmm.

UPDATE: I have found evidence (here) that Oca roots produce an exudate which suppresses growth in competing plants. However, the chemicals are also beneficial - insecticidal, and pathogenicidal. At least some of the chemicals require UV light to be activated, (so effectiveness is restricted to the surface and first few mm of soil?).

UV light levels reaching the root exudates must be very low once the foliage has formed a canopy.

All interesting to know, but as is sometimes the case, science does not give a clear answer. Will Oca poison or protect its bicrop partner, or something between the two?
Well, it obviously does not seriously harm most crops, from the evidence of my own eyes, and the experience of generations of Andean Indians, who's traditional methods of cultivation include bi-cropping with maize, and mixed planting with other tuber crops.
It seems to still come down to 'suck it and see'.

UPDATE: Details and results of the allelopathy trial here.