The competition between three species of small-leaf floating plants which are frequently found in rice growing areas of northern Peninsula Malaysia.
Lemna perpusilla, Spirodela polyrhiza and Azolla pinnata were collected from rice fields in the following 5 locations in Malaysia: Genting (Penang), Kepala Batas (Penang), Alor Setar (Kedah), Kepala Batas (Kedah) and Simpang Empat (Perlis). The pH values of the sites ranged from 6.52 to 7.22, the conductivity readings from 50 to 166 µS/cm, the oxygen (DO) measurements from 5.8 to 8.3 mg/litre and the nutrient concn, particularly of soluble reactive phosphate (SRP) and ammonia-nitrogen (NH3-N), from 0.034 to 1.342 mg/litre. Laboratory experiments showed that the max. growth increase for the 3 plants was at SRP concn of 0.01 mg. L. perpusilla, S. polyrhiza and A. pinnata increased their areal coverage 110-, 33- and 40-fold, resp., in Hoagland solution within 12 d. From competition studies, it was observed that L. perpusilla was the most dominant species, followed by S. polyrhiza and A. pinnata, resp. When rice seedlings cv. MR 81 were grown with 100% areal coverage of these 3 plants in Hoagland solution, no significant differences in the growth rate of the crop plants were observed.