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The Chemistry and Fertility of Soils under Tropical Weeds 79

different weeds. Salam et al. (1997e) observed in Oxisols Gedongmeneng that the
root zones of Alang-alang (Imperata cylindrica L.) showed a higher pH value than
those of Amaranth (Amaranthus tricolor L.), pigweed (Amaranthus spinosus L.), and
Green Kyllinga (Cyperus kyllingia L.), i.e. 6.25, 5.64, 5.03, and 5.01, respectively.
These data show that pigweed (Amaranthus spinosus), and Green Kyllinga (Cyperus
kyllingia L.) acidify the soil more significantly.

5.2 Effects of Alang-Alang

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Alang-alang (Imperata cylindrical L.) is unique. Instead of producing H ions,
the presence of this weed alkalinized soils. Salam et al. (1997e) observe in Oxisol
Gedongmeneng that the root zones of alang-alang (Imperata cylindrica L.) showed
a higher pH value than those of pigweed (Amaranthus spinosus L.), Green Kyllinga
(Cyperus kyllingia L.), and Amaranth (Amaranthus tricolor L.). The pH in the root
zones of these vegetation were 6.25, 5.03, 5.01, and 5.64, respectively (Fig. 5.2).
The significant difference in the pH measurement (0.64–1.24 units) indicates that
Alang-alang possesses an extraordinary adaptability. Its adaptability is also
observed by the higher activities of phosphatases in alang-alang root zones than
those in the other vegetations (Fig. 5.3).
Theoretically, the soil pH in the root zones of tropical weeds is lower due to
significantly higher amounts of cations than those of anions present in soil water so
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that weeds root excrete more H than OH . The higher pH in the root zones of
alang-alang indicates that this weed absorb more anions than cations.
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Consequently, roots of alang-alang excrete more OH than H .
Other observations show that grasslands show higher humus contents and,
thereby, grasslands show higher CEC and base saturation and generally more fertile
and also show higher pH (Harpstead et al., 1988). The leaves of grasses are more
alkaline, contain more Ca and Mg and, thereby, cause higher pH than do the needle
leaf plants. The leaves of broad leaf plants show higher pH than do needle leaf
plants, but show lower pH than grasses (Harpstead et al., 1988).

Abdul Kadir Salam and Nanik Sriyani – 2019