Page 55 - Ilmu Tanah

42 The Chemistry and Fertility of Soils under Tropical Weeds

environmental weeds, which may negatively affect plant biodiversity. Hejda et al.
(2009) conclude that most invasive weeds may decrease the species population
and biodiversity of plant community. Therefore, the introduction of plants needs
previous intensive study on the plant biology and physiology.

3.3 General Effects of Tropical Weeds on the Soil

Environment

As pioneer plants during succession, weeds may preserve the equilibrium and
sustainability of an ecosystem. The presence of weeds in the environment may
physically lower the soil erosion and chemically increase the soil organic matter
content and accelerate the nutrient cycles. Weeds are also environmentally
present as foods for animals, shades for birds and predators for pests and diseases,
as well as genetic sources for plant breeding (Adkins, 1997). Some other uses of
weeds have been investigated and applied for human welfare, among which the
use of weeds as raw materals for medicines and cosmetics, raw materials for foods
and feeds for animals, and also their uses in creative industry and arts. Some other
uses are as raw materials for biopesticides. Rhizomes of alang-alang (Imperata
cylindrica) and leaves of Oxalis corniculata (blimbingan) have long been known
as fever medicine. Pegagan (Centella asiatica) has been used for a fat burner in
a diet and is developed for medicine of cancers.
Good weed management had been shown to drastically decrease the soil
erosion in hilly coffee plantation of West Lampung (Sriyani et al., 1999). The
amount of soil eroded in manual weed control plot (manual weeding) was 25.270
-1
-1
kg ha 6-month . However, if the land was covered by natural plants, the soil
-1
-1
erosion was drastically reduced to 124 kg ha 6-month . The rate of erosion was
even lower in the experimental unit covered with Paspalum conjugatum to be 29
-1
-1
kg ha 6-month or about 99% lower (Table 3.1).
These phenomena show that the use of P. conjugatum and natural weeds
decreased the levels of soil erosion in coffee plantation. However, the total
coverage of land with weeds may cause environmental problems. Farmers must
intensively manage weeds so that they may not disturb the main plants. The
presence of weeds may cause more pests and deseases because lands are shaded
and moisturized. Limiting weed coverage only in particular parts of lands like

Abdul Kadir Salam and Nanik Sriyani – 2019