From the MetMuseuam.org:
"One of the major focuses of ceremonial life among the Abelam people of northeast New Guinea is the competitive growth and exchange of long yams. The Abelam cultivate two distinct categories of yams—a small variety used as ordinary food and long yams, massive tubers that can be as much as twelve feet long. A man’s social status is determined largely by his success in growing long yams.
Each man has a permanent exchange partner to whom he ceremonially presents his largest yams following the annual harvest, later receiving those of his rival in return. Men who are consistently able to give their partners longer yams than they receive gain great prestige. Lavishly adorned for the presentation ceremony, the finest long yams are essentially transformed into human images, decorated in the manner of men in full ceremonial regalia. The “heads” of the enormous tubers are adorned with specially made yam masks such as this one, which are made exclusively for yams and are never worn by humans."