This intriguingly unique poem has an overall tone and a secondary, middle tone along with a tertiary (third) tone.
The overall tone is heard in the first six and last two lines. In between are the two other tones, the secondary and the tertiary.
The overall tone begins with the first line then melds into the secondary tone part way through the seventh line: "Your beautiful black blood that irrigates the fields." The secondary tone carries on from there to "But a grave voice answers me," which introduces the tertiary tone before the poem returns to the original, overall tone. Knowing where these divisions are will you help you to identify the tones when you reread the poem and look for these tones yourself. Now, what are these tones?
Tone is the feeling or emotion expressed by the poetic speaker or persona toward the subject or characters being written about: tone is what the speaker feels about what is being said. The first tone, the first expression of the speaker's feeling, is triumphal. A triumphal feeling is a celebratory feeling. The speaker feels triumphal when he reflects on Africa because it is a proud homeland lineage full of images of might and greatness, as his grandmother sings of it.
The secondary tone in "Your beautiful black blood that irrigates the fields," is a tone sadly desperate. The speaker is saddened by the images of backbreaking labor under the whip of slavery and desperate to know if this whipped Africa is the same Africa that his grandmother triumphally sings about, the Africa that flows through his veins.
The tertiary tone is spoken by "a grave voice" (perhaps a collective voice from the grave) and is a gentle yet earnest tone that gently reprimands while earnestly exhorting. This gentle, earnest tone expresses the feeling of the "grave voice" as it points the speaker, who is like an "impetuous child," toward the correct present-day image of Africa: Africa is not the image of bent and whipped backs but the image a tree, "young and strong," that is acquiring and bearing the fruit of liberty:
That is your Africa springing up anew
Springing up patiently, obstinately
Whose fruit bit by bit acquires
The bitter taste of liberty.