Growth response of radiata pine to superphosphate on a second rotation site at Scarsdale.  B. Tomkins and P. Hopmans.  August 1990.  13pp. (unpubl.)

SUMMARY

Growth responses to superphosphate applied at establishment at rates of 0, 180 g tree^-1, 600 kg ha^-1 and 1200 kg ha^-1 to Pinus radiata on a second rotation site in the Scarsdale plantation (Victoria) were measured at periodic intervals for 11 years. The trial was carried out in order to compare growth responses to broadcast application of superphosphate at the time of planting at two rates with the traditional spot application at establishment.

Fertilisation at planting stimulated regrowth of competing vegetation which increased mortality and resulted in highly variable stocking. Nevertheless a substantial response in basal area and height was found for all three rates of superphosphate application. The results are comparable with findings from other studies which showed that response can be expected to continue through to rotation age with a commensurate increase in site productivity. The best response was obtained to a broadcast application of superphosphate at a rate of 600 kg ha^-1 which increased volume at age 11 years by 74 m³ ha^-1. There was no significant difference in response between the three fertiliser treatments. However, foliar phosphorus levels indicate that growth of trees treated with superphosphate at 180 g tree^-1 is likely to decline during the next few years.

Foliar analysis of phosphorus levels indicates the need for a follow-up application of superphosphate before age 4 years to trees receiving the spot application to maintain tree health and prevent phosphorus deficiency. Broadcast application of superphosphate at a rate of 600 kg ha^-1 at planting appears to be a viable alternative to the presently recommended regime for phosphorus deficient sites of a spot application of 180 g tree^-1 at planting followed by broadcast application of 700 kg ha^-1 before age 4 years. However, effective weed control must be provided in order to optimise the growth response and maintain satisfactory stocking levels.