Weed control is essential to improve plant productivity under an organic farming
system. This practice often leads to shifting of weed species. The experiment confirmed that
two-month solarization treatment brought about the alteration of weed species, but the number
of weed species was not significantly different, approximately fifteen species for each treatment.
Solarization treatment led to weed shifting and dominance from grass to broadleaf weeds. Red
plastic mulch shifted Blumea lacerna dominance to Ricardia brasiliensis at 0-5 cm depth.
Meanwhile, at 10-15 cm soil depth, the dominance of Eleucine indica was shifted into Bidens
pilosa. Mulch treatment substantially reduced the number of weed population to the depth of 15
cm from the soil surface. After two months of solarization, clear plastic mulch is the most
effective to reduce weed dry weight. Solarization significantly decreased weed dry weight by
approximately 30, 60 and 65 % in treatments using silver black, black, and clear plastic mulch
respectively in comparison to the control.