Page 50 - Ilmu Tanah

The Chemistry and Fertility of Soils under Tropical Weeds 37

decreased including Burkholderia, Gp6, Gp1 and Gp4 in the applied treatments at
genus level as compared to control treatment.
As pointed out previously, weeds also excrete several substances among which
+
are H and organic acids. These substances may lower the soil pH and cause the
changes in the adjacent soil chemical and fertility properties. The decrease in soil
pH may cause the increase in soil metal elements released from the speeded soil
mineral weathering. The presence of organic acids may also cause parts of the
metal elements to dissolve in soil water. The increase in soil organic matters by the
presence of weeds may increase the soil CEC, which also indirectly influence the
dissolved metal elemens.
Even though the impact of weeds related to their controls and their root
excretion like alellophatic substances and organic acids is significant, the negative
effects of weeds on animal and human health are not much in the current
literature. Among those reported are the allergic reaction caused by Ambrosia
artemisiifolia and Rhuss spp. and the poisoning effect of Solanum nigrum and
Rhuss spp. on animals. Data of weed effect on human and animal heath in
Indonesia is limited, less than those in some developed nations. It was not less
than 280.000 sheeps and 264.000 goats were predicted dead every year in the
United States of America caused by poisonous weed consumption. Some weeds
like Cynodon dactylon (Grintingan), Eleusine indica (Lulangan), dan Sorgum
halapense (Glagah), as well as Mimosa invisa (Kucingan) and Cyperus rotundus
(Teki) may cause allergy and wounds on animals and Ipomoea triloba (Mantangan)
may cause diare on goats (Sembodo, 2010). Some of these weeds are depicted in
Fig. 3.1 and Fig. 3.2.
A high amount of labors, time, and fund are also needed yearly to control
weeds, not because of the weed effects on crop production, but of the value of
natural beauty of lands. For example, the weed control in recreation lands, golf
courses, dams for recreation, etc. The presence of weeds may decrease the values
of the natural beauty of these lands and lower their selling prices. The presence of
weeds in golf courses may enhance the cost of maintenance significantly. Other
impact difficult to predict is the destruction of esthetic value caused by the
presence of weeds around roadsides, buildings, offices, campuses, sport fields, rail-
road sides, irrigation ditches, etc. In addition to decrease the natural beauty, the
presence of weeds may also enhance the maintainance cost.

Abdul Kadir Salam and Nanik Sriyani – 2019