The experiment reported in this paper was initiated in May 2007 at the Shenyang Experimental Station of Ecology, Chinese Academy of Sciences (N 41°31′, E 123°24′), and ran for two growing seasons, until October 2008. This region has a continental monsoon climate with a mean annual temperature of 7.0–7.9 °C and an annual precipitation of 700 mm. The test soil is classified as a Hapli-Udic Cambisol (FAO Classification), with organic matter content of 1.31%, pH (H2O) 6.80, 21.40% sand, 46.50% silt and 32.10% clay at 0–20 cm depth. No pesticides and herbicides have been used on the plots investigated in the study since 2003.
Two rice varieties, PI312777 and Liaojing-9, were used in the experiment. PI312777, an allelopathic rice line, was originally identified from the USDA-ARS rice germplasm collection and exhibited weed suppression in both US and Chinese paddy fields [8]. Liaojing-9 is a commercial cultivar in Northeast China and does not have allelopathic traits. The seeds of E. crus-galli used in this study were collected from the paddy field at the experimental station described above. The seeds were dried under sunlight and then stored in sealed glass jars prior to use.