Apart from the benefit of being able to grow in poor soils and its high yield, the plants can also take acidic soils and they like high rainfall and cloudy weather. That fits perfectly with the climate and conditions in Western Washington. The natural soil pH here is around 5.5 and annual rainfall is around 50 in (127 cm).
The plants are also very disease and pest resistant, as they contain natural bactericidal, nemocidal, and insecticidal compounds. I've read that they're grown in a polycrop system with potato, oca, and ulluco, and help to control pest problems in the crops surrounding it. I haven't tried that, but it seems like an intriguing possibility.
Personally, I think mashua has some promise as a livestock feed, given how productive it is. I've read that the tubers may need to be baked before feeding to livestock due to the presence of isothiocyanates that could cause health problems (these break down with cooking, and small amounts can be safely eaten raw by humans), so keep that in mind if you want to give it a try. It should also be noted that mashua have a reputation of being an anaphrodisiac (sex drive killer) for men. In an experiment done on rats that were fed mashua, their testosterone levels dropped by half. So that's something you might want to keep in mind if you're thinking of making mashua a large part of your diet. In the Andes where it's cultivated and eaten, it was coupled with another plant, maca, which balanced out this effect.
Mashua are also fairly frost hardy and a mashua plant I grew in Olympia (and that I had forgotten about before the big freeze) survived the really low temperatures.
Like oca, the majority of mashua varieties only produce tubers after the fall equinox until frost kills back the foliage. However, the variety "Ken Aslet" is not dependent on day length for tuber formation and can be found for sale online.
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This was my first year growing mashua, and I started with several different varieties. I obtained seed tubers from the Occidental Arts and Ecology Center and also through Seed Savers Exchange (from Frank van Kiersbilck), and planted them this spring. I provided a trellis for them and they went pretty wild, sprawling all over and climbing about eight feet high. I planted them next to the oca and a few of the mashua plants were crowded a bit, but one plant produced over five pounds of tubers. All of the tubers in the picture below were produced off of that one plant:
Here's a picture of a mashua plant (surrounded by oca) taken about a month ago: