Germination and establishment of Amaranthus retroflexus were studied at different temperatures, planting depths, soil types, nitrogen supply and water potentials. The minimum temperature for seed germination was >5°C; maximum germination occurred between 35 and 40°C. At temperatures between 25 and 35°C, an additive effect on germination rate was observed when temperature and water availability were increased. For all soils tested, the percentage emergence of seeds placed on the soil surface and 4 cm deep was significantly lower than seeds placed between 0.5 and 3 cm. Emergence in the four sandy soils studied was generally greater than in the two heavier soils. There was a highly significant interaction between seed depth and soil type. Plant growth was also greatest in the lighter soils. Plant height, number of leaves, leaf area, fresh and dry weight, and nitrogen and carbon percentage in plant tissues of A. retroflexus increased significantly with increasing soil nitrogen supply.

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