Research Branch Report No. 186

Phosphorus cycling in radiata pine on a strongly adsorbing soil.  D. W. Flinn, J. M. James and P. Hopmans.  December 1981.  21 pp. (unpubl.)

SUMMARY

The fate of superphosphate, broadcast-applied at rates up to 1400 kg ha-1 to a four-year-old stand of Pinus radiata D. Don (radiata pine) established on a strongly adsorbing soil (phosphorus sorption maximum in excess of 3000 ppm), was studied over a three-year period. Levels of ‘available’ phosphorus (Bray No. 2-extractable) in the surface soil increased markedly within eight months of fertiliser application and then remained more or less constant for the remainder of the study. As a result, there was substantial uptake of applied phosphorus by P. radiata, as indicated by the phosphorus content of the above-ground components of fertilised and unfertilised trees. Increased phosphorus uptake was associated with a significant growth response.

Three-monthly sampling of needles of various ages, from the upper and lower crowns of trees fertilised with increasing rates of superphosphate, showed that root-absorbed phosphorus was preferentially distributed to the growing points, especially those near the tree apex. There was evidence of substantial internal cycling, with phosphorus being withdrawn from older needles prior to abscission. Fertiliser efficiencies of between 8.3 and 12.2%, according to the rate of superphosphate applied, were estimated during the short period of the study.

It was concluded that for soils similar to those in this study, where both iron and aluminium oxides make a significant contribution to phosphate retention, a localised application of superphosphate (about 180 g tree-1) at the time of planting, followed three to four years later by a broadcast application of the same fertiliser at a rate of no less than 700 kg ha-1 would ensure satisfactory growth of P. radiata over a rotation.

Also published:

Flinn, D.W., James, J.M. and Hopmans. (1982)  Aspects of phosphorus cycling in radiata pine on a strongly phosphorus adsorbing soil.  Aust. For. Res. 12: 19-35.