Hello,
Okay, so I'm still working on the poem, but I just wanted to point out that the poem seems to play with farming words and growing and harvesting rice.
A へら is the flat, metal part of a spade or plow, which I believe is being compared to the teeth of a demon here.
A にお is a circular stack of rice straw (like a straw bale), but this is a seasonal word for fall, not spring. Perhaps Nanpo didn't know that much about rice farming, and carelessly combined farming words?
Again, this is very rough and probably there are many points that are mistaken, but--in a non-poetic, non-5/7/5/7/7 translation, I think what the poem is saying is the following:
it was by the plow’s teeth of the demon
that the one who put mud on the rice bales
in the fields and left, was devoured in one bite.
I don't see any connection to the Akutagawa poem.
One thing that might be worth looking into is seeing if this poem appears elsewhere. By my observation, Nanpo seems to use certain poems for certain painting themes, and they are often ones he's already written and published elsewhere. The Ōta Nanpo zenshū might give a clue to the origin of this poem.
Could we see the painting, please? That might help a bit.
I'll see if I can refine a bit, but I welcome any corrections to my initial musings or thoughts from the rest of the community.
Best wishes,
Leah Justin-Jinich (She/her/hers)
PhD Candidate
Department of East Asian
Languages and Civilizations
Harvard University