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The Chemistry and Fertility of Soils under Tropical Weeds 95

by plants roots and soil macroorganisms. In this situation, soil microorganisms may
progressively develop their populations and increase their activities (Yusnaini et al.,
2007). Their activities may be measured, among others, by measuring the CO 2
evolution and also enzymatic activities (Salam et al., 1998b; 1999a; 1999b; Yusnaini
et al., 2007). The increase in the evolution of CO 2 as a result organic matter
addition is shown in Table 6.4. Hellmann et al. (1997) report that the emission
rates of carbondioxide (CO 2 ), and also methane (CH 4 ) and nitrous oxide (N 2 O),
increased successively during compost maturation. Green manure and chicken
manure significantly increased the activities of soil microorganisms as shown by the
increase in CO 2 evolution. The effect of the chicken manure was also shown to be
more significant at increasing the soil microbial activities than did the green
manure.

Table 6.1. The chemical reactions in photosynthesis and respiration.

PHOTOSYNTHESIS
+
-
A CO 2 + 4e + 4 H  CH 2 O + H 2 O (Ox. State C: 4+  0)
+
-
D 2 H 2 O  O 2 + 4e + 4 H (Ox. State O: 2-  0)
R CO 2 + H 2 O CH 2 O + O 2
RESPIRATION
-
+
D CH 2 O + H 2 O  CO 2 + 4e + 4 H (Ox. State C: 0  4+)
- +
A O 2 + 4e + 4 H  2 H 2 O (Ox. State O: 0  2-)
R CH 2 O + O 2  CO 2 + H 2 O
A = Electron Acceptor; D = Electron Donor, and R = Redox Reaction

Table 6.2. Some hydrocarbons as sources (electron donors) of
energy for soil organisms.

1 Organic Matter Lignin (C 2.8 H 2.9 O)
(Individual) Cellulose (C 2.2 H 2 O)
(Dry/Fresh)
2 Litters (1/3 Lignin 2/3 Cellulose)
+
4+
C 1.7 H 2.2 O  1.7C + H 2 O + 0.2 H + 7e -
-
4+
3 Organic Matter C 2.2 H 2.2 O  2.2C + H 2 O + 0.2 OH + 9e -
(whole)
After Bohn et al. (1985)
Abdul Kadir Salam and Nanik Sriyani – 2019