Phosphate (P) Sources and Irrigation Supply Influence Yield and Transpiration Water Use Efficiency in Grain Amaranth (Amaranthus cruentus L.)

Studies have shown low soil P and water availability as major constraints to grain amaranth (Amaranthus cruentus L.) production in sub-Sahara Africa (SSA). Effects of phosphate sources (single super phosphate-SSP; Sokoto rock phosphate-SRP; Ogun rock phosphate-ORP) and water supply were therefore determined on yield and transpiration water-use efficiency (WUET) of dual purpose (vegetable + seed) grain amaranth in pots in a glasshouse at Ibadan (7 degrees 54'N; 7 degrees 30'E, 213 m above sea level), Nigeria. Phosphate sources and water supply had significant effects on yield and WUET. Compared with the control plants, which had adequate water and P available to them, yield was reduced by 32% with low water supply and by 46% with low P supply. Under adequate P-supply, water stress increased WUET by 56%. Under adequate water supply WUET did not differ significantly between P-sources but was in the order SSP>SRP>ORP. These indicate the potentials of using rock phosphate as alternative phosphate source and efficient water use in SSA irrigation systems.