Phosphorus nutrition of Ilex crenata 'Helleri' grown in a pine bark medium

Abstract

The purpose of this research was to characterize the phosphorus nutrition of Ilex crenata 'Helleri' and pine bark P relationships. Branched liners of 'Helleri' holly were grown in a pine bark medium in which 0, 5, 10, 15, 20, 25, or 30 ppm P were maintained. Shoot dry weight increased as the pine bark P level increased to 10 ppm P, while root dry weight decreased with increasing pine bark P levels. Total mg of P in shoot tissues continued to increase with P treatments higher than 10 ppm, indicating luxury consumption of P. Total mg of P in root tissues increased to the 10 ppm P treatment. Total µg of Fe, Cu, and Zn in shoot tissues followed the dry weight response, increasing to the 5-10 ppm P treatment then tending to decrease as pine bark P levels increased. Root tissue Fe was erratic while Cu did not vary with treatment and Zn decreased with increasing pine bark P levels. Total µg of Mn in shoot tissues increased with P treatments while total µg of Mn in root tissues decreased with increasing pine bark P levels. Dry shoot weights of 'Helleri' holly grown in a pine bark medium amended with either 270, 540, or 810 g/m³ of P or fertilized with 10 ppm P were not different while root dry weights decreased with increasing pine bark P levels. Water extractable P for the 810 g/m³ treatment decreased 245 ppm during the experiment and by week 5 was below 10 ppm. Amending the pine bark medium with 270 g/m³ of P did not increase the dry shoot weight of ‘Helleri’ holly when subsequently fertilized with a complete slow-release granular or water soluble fertilizer. The pine bark medium contained indigenous P which leached rapidly. When ‘Helleri’ holly were fertilized with a nutrient solution without P, 0.08 mg of indigenous P were absorbed. The pine bark adsorbed 7.5 µg of P per g of pine bark when equilibrated with a 10 ppm P nutrient solution. These studies indicate that maintaining 10 ppm P in the pine bark medium results in the greatest dry weight of 'Helleri' holly. A stable pine bark P level was not attained with superphosphate-amended pine bark, thus superphosphate is not recommended as a P source. Pine bark P relationships revealed that ‘Helleri’ holly absorbed indigenous P while a negligible amount of P was bound by the pine bark compared to the amount of P used by a ‘Helleri’ holly grown in a 1 liter container.