GRAIN-YIELD FORMATION AND NITROGEN UPTAKE OF AMARANTH

The aim of the present study was to evaluate amaranth grain production , nitrogen extraction from the soil and nitrogen distribution into gra ins and vegetative crop residues under Western European conditions. Tw o field experiments were conducted at Stuttgart (South Germany) in the years 1992 and 1993 without any nitrogen fertilizer. Four genotypes w ere planted (K-432, K-343, MT-3 and A-10). In 1992 three sowing dates (May-June) and in 1993 two sowing densities (40, 100 seeds m(-2)) were tested. Biomass production, nitrogen uptake and distribution were obs erved between flowering of plants and (manual) harvest of grain yield. Amaranth genotypes produced 720-1320 g m(-2) total biomass and 140-30 0 g m(-2) grain. The nitrogen uptake was 13-21 g N m(-2). Because of t he low harvest index (less than or equal to 30 per cent), up to 14 g N m(-2) remained in the residues (straw+roots) after harvest. The N har vest index was highest with K-432. One year's results suggested that t he optimum sowing date was about middle of May, the optimum density ab out 30-40 plants m(-2). MT-3 was severely infested by leaf spot diseas es.