Effect of aqueous extracts of Populus deltoides M. on germination and seedling growth. 1. Wheat

Laboratory study was carried out to investigate the allelopathic effects of 3 and 4 year old poplar (Populus deltoides) trees existing in irrigated ag ricultural land, on wheat crop. The experiment consisted of field data and two bioassay studies with aqueous extracts of partially decomposed leaves o f poplar and that from surface soil. In the field, performance of wheat pla nted in poplar field with boundary plantation was determined. In the first bioassay, three concentrations (0.45, 0.90 and 1.40 g leaf l(-1)) of aqueou s extract of partially decomposed leaves of poplar (0, 30, 90, 145 and 365 days after soil incorporation in litter bag) were studied on germination an d seedling growth of wheat. The distilled water was served as control. In s econd bioassay, aqueous extract of surface soil (0-15 cm), collected from 0 -3, 3-6, 6-9 and >15 m(control) distance from tree line of 3 and 4 year old poplar trees was used. The aqueous extract of soil collected from > 15 m f rom the tree line was used as control. The aqueous extracts of partially de composed poplar leaves retarded the germination and growth of wheat. Relati vely more retardation was noticed with extracts from partially decomposed l eaves and the magnitude of reduction was greeter during the initial stages of decomposition. Irrespective of decomposition stage, adverse effect was i ntensified with increase in concentration of extracts. Germination and grow th of wheat were suppressed by extract of soil sampled from a distance of 0 -3 m with 3 year old plantation, which further intensified and extended up to 6m in fourth year. Thus, adverse effect of aqueous extracts of soil unde rneath poplar tree indicated the accumulation of allelochemicals in the soi l and the effect was more pronounced with advancement of tree age. Results of the laboratory study confirmed the field observations.