LONG-TERM FOLIAR PHOSPHORUS RESPONSE OF PINUS RADIATA TO SUPERPHOSPHATE FERTILISER

Foliar phosphorus concentrations have been recorded for up to 15 years in the seven blocks of a long-term trial monitoring phosphorus fertiliser applica tion rates on Pinus radiata* D. Don. In unfertilised plots on the most deficient sites foliar phosphorus concentrations have not altered greatly from 0.06% P (o.d. wt) over time, but at the less deficient sites foliar phosphorus has tended to decline over time. In fertilised plots there was an immediate increase in foliar phosphorus, proportional to the amount of fertiliser applied, followed by a slow decline over time. After thinning there tended to be a rise in foliar phosphorus lasting for about 2 years. A simple multiple regression model explained 73% of the total variation. Further variation in foliar phosphorus associated with annual fluctuations accounted for only 5% of the total.