Effects of environmental factors on germination and emergence of Amaranthus retroflexus

Detailed knowledge about the environmental conditions required for weed see d germination and establishment in soil is an important prerequisite for th e development of integrated and biological weed control strategies. Germina tion and establishment of Amaranthus retroflexus were studied at different temperatures, planting depths, soil types, nitrogen supply, and water poten tials. The minimum temperature for seed germination was > 5 C; maximum germ ination occurred between 35 and 40 C. At temperatures between 25 and 35 C, an additive effect on germination rate was observed when temperature and wa ter availability were increased. For all soils tested, the percentage emerg ence of seeds placed on the soil surface and 4 cm deep was significantly lo wer than seeds placed between 0.5 and 3 cm. Emergence in the four sandy soi ls was generally greater than in the two heavier soils included in the stud y There was a highly significant interaction between seed depth and soil ty pe. Plant growth was also greatest in the lighter soils. Plant height, numb er of leaves, leaf area. fresh and dry weight, and nitrogen and carbon perc entage in plane tissues of A. retroflexus increased significantly with incr easing soil nitrogen supply.