This test was conducted in a greenhouse with an average temperature of 26°C. The ground residues 5 g of 114 rice cultivars were mixed thoroughly with 500 g of silica sand in each pot. All pots were steam-sterilized for 5 h before use and were placed on saucers to prevent the loss of water-soluble toxic substances (Chung and Miller, 1995). Plastic plugs were placed in the bottom of each pot to prevent the loss of sand through the holes in the bottom. One hundred surface-sterilized E. crus-galli seeds were planted uniformly 1 cm deep in each pot after two weeks of residue incorporation. Emergence was defined as the coleoptile protrusion through the soil surface and was measured each day for 14 days after planting. After emergence, the seedlings were thinned to 25 plants per pot. Hoagland's solution I (80 ml; Hoagland and Arnon, 1950) was added every four days to each saucer to maintain adequate moisture. All plants were harvested 14 days after planting. All plants from each pot were measured for shoot length, and the seedlings were dried at 65°C for 4 h to determine dry weight. Control plants were grown in silica sand without residue. The percentage inhibition was calculated using the following equation ( Chung et al., 2001):