Field studies were conducted at the vegetable research plots of NIHORT, Ibadan to investigate the effect of different phosphorus (P) sources on the growth and yield of grain amaranth (A. Cruentus L). The experiment was arranged as a split-split plot factorial fitted to a randomized complete block with three replications. The main plots were the sources of phosphorus (Single Super Phosphate SSP and Sokoto rock phosphate SRP); the sub-plots were P rates (0, 30 and 60kg/ha); and the sub-sub plots were the grain amaranth varieties (NH84/452-v1; NH84/453-v2; and NH84/493-v3).
Results indicated that P sources significantly influenced grain yield and application of P significantly increased amaranth leaf fresh weight (LW), Stem fresh weight (SW), Root fresh weight (RW) and Grain yield (GY). Relative Agronomic efficiency of SRP compared to SSP was 63%. The optimum P rates for Leaf Number (LN) and leaf Area (LA) production in amaranth ranged between 30 and 60kg p/ha. Grain amaranth varieties V1 and V3 were significantly taller than V2 (P<0.05). Results of these studies suggest that Sokoto Rock phosphate could be an alternative source of P for grain amaranth production.