Fluorescence Characteristics of Humic Acid in Chinese Black Soil under Long-Term Fertilization

Figure 4

Clustering tree of the scores of the two principal components for all the field treatments (a) and the changes in humification indices ((b)–(h); see text for details). CK=control, NPK= NPK fertilizer, OM=organic manure, and MNPK=manure + NPK.

(a)

(b)

(c)

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(e)

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(h)