Page 105 - Enzymes in Tropical Soils

Enzymes in Tropical Soils 93

140 Gedongmeneng
Activity (mg p-NPP g -1 h -1 ) 100 Tanjungan
120

Banjaragung
80
Gisting
60
40
20

0
1 2 4 8 12
Time (weeks)

Fig. 6.7. The time dependence of soil acid phosphatase activity in Lampung (Indonesia)
soils (Adapted from Salam, 1998a)

The above phenomena are easily understood because water is one
important reactant in the decomposition of organic matters used by soil
microorganisms and macroorganisms as energy sources. For example, the
decomposition of organic P and organic S progress with the reactions shown in Eq.
4.1 and Eq. 4.5, respectively. These equations suggest that the presence of water
molecules is a prerequisite for the reactions. The absence of water in soils may
stop the decomposisiton of organic P and organic S. The more the amount of
water molecules is available in the soil system, the faster the rates of
decomposition of the organic sources of nutrients. Curtin et al. (2012) showed that
the organic matter decomposition was linearly related to the soil gravimetric water
content.
In addition to water, soil microorganisms and macroorganisms also need
heat for their growth and development; meaning that their lives are dependent on
0
soil temperature. Most researchers agree that 30 C is an optimum value for
0
organisms to have a maximum growth; therefore, 30 C is usually used to determine
0
the maximum activity of soil microorganisms. Lower temperature below 30 C may
decrease the metabolisms in the microorganism bodies whereas temperature

Abdul Kadir Salam - 2014