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The Chemistry and Fertility of Soils under Tropical Weeds 41

Some weeds are pioneer plants due to their fast growing characteristics and
their ability to propagate extensively with short life cycle. Alang-alang (Imperata
cylindrica) is a very good example. This weed may produce 44 new rhizomes of 13
m long with as many as 646 tubers in 18 weeks of growth (Sriyani, 1993). An
experiment in di Gunung Madu Plantation, Central Lampung, shows that a three
month growth of on tubers of teki (Cyperus rotundus) in the absence of other
weeds produced as many as 524 new tuber. This data show that weeds
demonstrate the ability to quickly produce vegetative and generative organs such
as rhizomes or tubers.
The biological invasion grows with modern transportation, global trade,
transportation of germ plasms for research and development, biological
conservation, and also tourisms. Biologists and weed scientists are now aware that
the spread of weeds is not only by winds or water, but also by human. Human
spread most beneficial plants from one area to others. This activity may sometime
cause disasters. For example, alang-alang was imported into the United States of
America from tropical lands for land conservation to cope with erosion and
landslide problems but after years became a serious weed in some states of the
country like Florida and Louisiana (Tabor, 1949). Kogan and Jepson (2007) argue
that biological invasion influence not only the local species and agroecosystem but
also the food safety and security as well as public health. Acacia nilotica (Prickly
Acacia), a native plant of the subtropics of Africa, Middle East, and India, was
brought to Australia for an esthetical plant and later for a shading plant for animals
in pasture but later become weed in animal pasture (Bolton, 1989). This plant is
also a serious weed in the National Park of Baluran, East Java, while Meremia
peltata invaded the National Park of South Bukit Barisan, West Lampung, and
endangered the local plants. The invasion of Acacia nilotica is also reported to
disturb the ecosystem, lower the existing biodiversity, and endanger the
population of wild bulls (Bos javanicus) (Siregar dan Tjitrosoedirdjo, 1999).
Most of plants introduced into Indonesia were important crops like rubber, oil
palm, cacao, soybean, corn, and cassava (Tjitrosoedirdjo et al., 2016). However,
some plants introduced become invasive like eceng gondok (Eichornia crassipes),
akasia arabika, kirinyuh (Chromolaena odorata), and sembung rambat (Mikania
micrantha). Most of the 75 invasive plants reported by Tjitrosoedirdjo et al. (2016)
have long been known as weeds in agricultural lands and some are important
weeds in Indonesia like Imperata cylindrica (alang-alang), Eichornia crassipes
(eceng gondok), Mimosa pudica (putri malu), and Mikania micrantha (sembung
sambat) shown in Fig. 3.2. Some weeds also exist in non-agricultural lands called

Abdul Kadir Salam and Nanik Sriyani – 2019