Page 113 - Ilmu Tanah

100 The Chemistry and Fertility of Soils under Tropical Weeds

Koths, 1980; Trasar-Cepeda and Gil-Sotres, 1987; Joner and Jakobsen, 1995; Deng
and Tabatabai, 1996).
One of the indicators of the decrease in soil organic C is the decrease in soil
enzymatic activities in intensively tillage soils. Salam et al. (1998c) also show that
the activities of acid phosphatase in minimum tillage or no tillage soils were higher
than those in intensively tillage soils (Table 6.6). Previously, Klein and Koths (1980)
also report that the activities of urease, protease, and acid phosphatase were all
higher in no-tillage soils than those in plowed soils. Bergstrom et al. (1998a) also
report that the activities of soil enzymes including dehydrogenase, urease,
glutaminase, phosphatase, arylsulfatase, and -glucosidase, increased in no tillage
soils.

Table 6.6. The changes in soil phosphatase activity as
affected by soil tillage*.

-1
Urea (kg ha )

0 100 200
Soil Tillage
-1
-1
....... g p-Nitrophenol g h .......
Intensive Tillage 157 142 140

Minimum Tillage 187 174 173

No Tillage 169 163 181

Average 171 160 165

*Adapted from Salam et al. (1998c)

6.4 Effects of Continuous Cropping

Cropping may change the contents of C, P, N, and S of soils through root
excretion and plant residues. The amounts contributed by plants are dependent on
the type and duration of cropping (Fig. 6.5). Continuous cropping with similar
crops may build significant amount of these elements. Crops associated with N 2

Abdul Kadir Salam and Nanik Sriyani – 2019