A Physiological Effect of Nitrogen on Phosphorus Absorption by Corn1

A series of soil and solution experiments were conducted to study the mechanism responsible for the increased P absorption which occurs when N is added to a P fertilizer band. The addition of (NH4)2SO4 or NH4Cl to a pellet P‐32 labelled, concentrated superphosphate placed 0.5 inch to the side of a corn root greatly increased the labelled P content of the plant tops. The addition of KNO3 reduced the P content of the tops when compared to concentrated superphosphate only. When the pellets consisted of phosphate only or phosphate plus KNO3, labelled P accumulated to high levels in the root as revealed by autoradiographs. No such accumulation occurred in the presence of NH4+ ions. The addition of NH4NO3 to a nutrient solution increased the transfer of P through a 1‐inch segment of a corn root exposed to the solution, but did not influence the accumulation in the root. It was concluded that the NH4+ ion has a specific influence on the transfer of P across the root symplast to the xylem.