Phosphorus Absorption During Various Growth Stages of Spring Wheat and Intermediate Wheatgrass¹

Solution cultures were used to study the importance of P absorption during various growth stages of spring wheat and intermediate wheatgrass. Phosphorus was not needed in the solution cultures during all growth phases of the two crops. A supply of P for the first 5 weeks (up to heading for wheat) was adequate to produce maximum dry matter for both species and for maximum grain production of wheat. Maximum root development was achieved when P was supplied for the first 4 weeks of growth. Although plants absorbed only small quantities of P prior to tillering, this amount was important. When P was withheld for the first 2 weeks, tiller and secondary root development was hindered. Yields of wheat and wheatgrass tops and wheat grain were only 80, 59, and 42% of maximum, respectively. Although P uptake occurred after wheat headed, this P was not utilized for dry matter or grain production. Maximum accumulation of P occurred when P was initially withheld, but supplied later until harvest.