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80 The Chemistry and Fertility of Soils under Tropical Weeds

7

6
pH

5

4

Fig. 5.2. Effect of amaranth and soil tropical weeds on soil pH.
(Adapted from Salam et al. (1997e), IC = I. cylindrica, AT = A. tricolour, AS = A. Spinosus, CK =
C. Kyllingia).

5.3 Effects on Soil Enzymatic Activities

All vegetation may enhance the soil enzymatic activities since their roots may
directly produce various soil enzymes. Data in Fig. 5.3 show that the presence of
weeds may vary the activities of soil acid phosphatase and alkaline phosphatase in
soil of Gedongmeneng (Oxisol). The activity of acid phosphatase is higher than that
of alkaline phosphatase indicating that this soil is dominated by acid phosphatase.
The activity of phosphatase is however dependent of the weeds. Alang-alang (IC)
is the most effective phosphatase producers among the four weeds, followed by
Amaranthus tricolor, Cyperus kyllingia, and Amaranthus spinosus; both for acid and
alkaline phosphatases. Kotroczo et al. (2014) also suggests that the soil phosphatase
and β-glucosidase show similar seasonal dynamics. Both enzymes show the highest activities
in spring coincidently related to the high soil moisture and high root activity. Therefore, it is

Abdul Kadir Salam and Nanik Sriyani – 2019