Page 107 - Enzymes in Tropical Soils

Enzymes in Tropical Soils 95

topsoil and subsoil samples stored at soil field water capacity were 1.7 – 1.9 times
higher than those stored at air-dry condition. The activity of phosphatase was also
reported to be higher in moistened soil sample untill 120% than those in an air-dry
soil sample (Salam, 1998a) as shown in Fig. 6.8. Salam (1998a) also showed that
the soil – water mixture must be incubated for several days to attain equilibrium, in
which the enzymatic activities were maximum. The results of experiment showed
that the activities of phosphatases in a japanese Ultisol after 14 day incubation
were higher that those after 7 day incubation at water content < 40%. Data
showed that the activities of enzymes in some Lampungese soils (Ultisol
Gedongmeneng and Tanjungan, Alfisol Banjaragung, and Andisol Gisting) increased
with time until 8 days of incubation showing the first order of kinetics.

180
160 7 days
Activity (mg p-NPP g -1 h -1 ) 120 14 days
140
incubation
incubation
100
80
60
40
20
0
0 0.4 0.8 1.2
Water to Soil Ratios

Fig. 6.8. The phosphatase activity as affected by water contents and
incubation time (Adapted from Salam, 1998a).

Previously, it was reported that the activity of phosphatase was higher in
no-tillaged soils than those in soils tillaged with a conventional method, related to
the higher water content in no-tillage soils (Klein and Koths, 1980). Kumar and
Wagenet (1984) showed that the activity of urease was linearly affected by soil
water content and was maximum at field water capacity (Fig. 6.9). Herbein and

Abdul Kadir Salam - 2014