Some poetic devices Lindsay uses in "The Flower-Fed Buffaloes" are personification, hyperbole, metaphor, and imagery. Lines 3 and 4 begin the personification. Personification is the giving of human qualities or behavior to nonhuman objects. In line 3, "locomotives sing" as though they were human. In line 4 "prairie flowers lie low" as though they were napping in the grass as humans might do.
Hyperbole is the use of exaggeration or overstatement to make something larger than it is and more impressive or emphatic. In the title and line 1, Lindsay opens with a beautiful hyperbolic image of buffaloes feeding on flowers. Of course they fed more on grasses than on flowers, but the overstatement makes the imagery more emphatic and the buffaloes more sympathetic.
Lines 5 and 6 offer the best example of imagery. Lindsay writes about the "The tossing, blooming, perfumed grass / Is swept away by wheat." Here he uses tactile imagery, visual imagery, and olfactory imagery. Imagery is language that calls up metal images in relation to things that can be felt (like tossing), seen (like blooming), smelled (like perfume), heard (like locomotives singing), or tasted (like flowers fed upon).
There are other examples of poetic devices. One example of metaphor is line 8 in which "spring" is called "sweet," implicitly comparing spring to a sweet treat--or to sweet tasting flowers: "In the spring that still is sweet." Repetition makes lines 4, 12, and 13 important to Lindsay's message of loss as he repeats "lie low" with the variation of "lying low."