Long-term growth and nutrition of second-rotation Pinus radiata on podzolised soils in response to residue management, weed control and fertilisation.  P. Hopmans and B. Tomkins.  March 1992. (unpubl.)

SUMMARY

Growth and nutrition of second rotation P. radiata on podzolised sands were evaluated for three methods of site preparation including retention of logging residues, and clearing of residues by windrowing or broadcast burning of residues followed by cultivation. Superimposed on these were weedicide and fertiliser treatments.

Retention of logging residues improved growth significantly compared with clearing or broadcast burning of the slash followed by cultivation, especially in combination with weed control and fertiliser at planting. Slash retention increased basal area by 29% at age 8 years. Mean tree diameter (DBHOB) at 5 years was strongly correlated with method of site preparation and levels of P in foliage. Levels of N and P declined from 15 to 11 mg g^-1 and from 1.5 to 1.1 mg g^-1 respectively, indicating a decline to marginal levels of these nutrients by age 8 years. Application of P fertiliser at this age resulted in a growth response strongly correlated with initial basal area, and growth continued to be consistently better where logging residues were retained. Average increments in basal area for the period between 8 and 15 years with retention of slash, clearing and ploughing, and broadcast burning and ploughing in combination with weedicide and fertiliser at planting were 24.0, 21.1 and 20.5 m² ha^-1 respectively. Application of P resulted in low N/P ratios in foliage indicating the need for N as well as P fertiliser.

P. radiata on these podzolised sands is strongly influenced by the management of residues remaining after clearfelling. Retention of logging residues, effective weed control and timely applications of N, P and Zn are essential to meet the nutrient demand of young P. radiata plantations and to optimise site productivity. Growth advantages gained early in the rotation are maintained well beyond the establishment phase, at least to age 15 years in this study. The results support a conservation-oriented approach to the silvicultural management of successive crops of P. radiata on these podzolised sands in southern Australia.