Introduction to Soil Chemistry

R 2C
R
organic compounds 63
O
C
–
O
Carboxylate anion
O –
Phenoxy (the anion of phenol OH)
Figure 3.11. The carboxylate anion (an ionized acid) and a phenoxy (the anion of phenol) groups.
The R stands for the rest of the humus molecule to which these groups are attached.
Figure 3.12. A basic extract of an organic soil is shown on the left; a sample of the sodium salt
of humic acid is seen on the right.
from an organic soil and a commercial sample of the sodium salt of humic acid
are shown in Figure 3.12.
Many researchers have attempted to unravel the mystery of the structure
of humus. One approach has been to isolate “fractions” by extracting humus