Page 108 - Enzymes in Tropical Soils

96 Enzymes In Tropical Soils

Neal (1990) also reported that the activity of phosphomonoesterase in wet tundra
soils were 20 – 30 times greater than that in drier soils. The activity of
phosphodiesterase was 25 – 35 times greater in wet tundra soils than those in the
drier soils. The vehicle disturbance decreased the activity of both enzymes in wet
soils but not in dry soils.
However, water content higher than the optimum values may cause a
negative influence on the soil biochemical reactions. Too much water may fill most
of the soil pores and may inhibit the O 2 diffusion into the soil system. Since the
enzyme producing organisms need O 2 for their respiration, the absence of O 2 may
depress the soil organisms and decrease the production of enzymes.

25

Activity (mg N g -1 h -1 ) 20

15

10

Fig. 6.9. The effect of soil water contents on the activity of urease
(Drawn from Kumar and Wagenet, 1984).

The rates of soil biochemical reactions are also controlled by soil
temperature (Dash et al., 1981; Harrison, 1983; Moyo et al., 1989; Neal, 1990).
Neal (1990) reported that the activity of phosphatase increased with the increase
0
0
in soil temperature from – 25 C to +5 C. Dash et al. (1981) reported that maximum
o
o
urease activity at 47 C among the soil temperature ranging from 0 to 57 C. Urea
o
hydrolysis rates in soil was shown to increase in soil temperature from 5 to 45 C
Abdul Kadir Salam - 2014