The extensive and valuable Radiata Pine (Pinus radiata) estate in Victoria has been established on a contrasting range of site types traversing deep infertile sands, to mining spoils to strongly phosphate-fixing soils. As would be expected for an introduced species, this wide range of soil types was commonly associated with nutrient deficiencies including phosphorus (P), nitrogen(N), boron (B), zinc (Zn) and calcium (Ca) in particular. To address these deficiencies required an analysis of the nutrient status of trees (primarily by analysis of needles carefully sampled from a specified part of the crown) and the nutrient status of soils (involving analyses for pH, salinity, exchangeable cations, total C and N, and total and extractable P as well as soil characteristics including infiltration capacity and depth to any impeding layer).

Conifer nutrition has a relatively long history in Victoria. In the early stages of plantation establishment, a fertilizer trial was established in 1950 on a failed first rotation site planted in 1920 at Anglesea. It tested the growth responses to soil cultivation and fertilizers (P, K, Cu and Zn) on three soil types identified by Prof. Leeper, a distinguished soil scientist at the University of Melbourne. After 10 years the trial was measured. The results indicated growth responses of Radiata Pine to soil cultivation and fertilizer that were reflected in the changes in nutrient status of trees as determined by foliage analysis (Raupach et al. 1975).

Another early fertilizer trial was established in 1964 in the Ballarat region where the productivity of plantations in the Ballarat/Scarsdale/Creswick areas was less than optimum. The trial examined the response to a range of nutrients including P which was considered to be the main limiting nutrient based on nearby agricultural experience This experience considered that Molybdenum (Mo) may also be limiting (Forestry Research No 3, 1964). A remeasurement of the trial at age one year suggested that “superphosphate will have the greatest effect on both height and diameter growth” (Forestry Research No 9, 1967).

Further trials were also initiated at Benalla and Myrtleford using Magamp (magnesium ammonium phosphate) and Wuxal (a foliar fertilizer), but responses were minimal (Forestry Research No 9, 1967).

A rapid expansion in research on the nutrition of softwood plantations and associated soils occurred in the early 1970’s, spearheaded by Dr Fred Craig (PhD in forest soils under Prof. Leeper) and Peter Hopmans (Chemist) who initiated a substantial and sustained research program into forest soils and tree nutrition. To facilitate this research program, laboratory facilities with up-to-date technology in terms of instrumentation and associated laboratory facilities were established for the analysis of soil and tree samples.

Research into the nutrition of Radiata Pine continued to gain momentum as new site types were planted in the era of a national program for self-sufficiency in softwood timber.

The research program transcended a wide range of aspects involving both plant nutrition for seedlings through to mature trees, to soil fertility including nutrient losses in harvesting and site preparation, to improvement in soil structure by organic matter additions (Flinn and Waugh 1983).

The program encountered some exceedingly complex challenges. These covered so called 2R decline where second rotation Radiata Pine stands on sandy soils in the Green Triangle region, centered on Mt Gambier, were found to be less productive than for first rotation stands. Nutrition R&D played a major role in successfully addressing this productive capacity problem (Flinn et al. 1979, Hopmans and Elms 2009). Ensuring maintenance of productive capacity of a site is a fundamental requirement of sustainable forest management. One of the new issues encountered across a number of site types (including former agricultural sites that had received significant fertilizer additions in their past management) was found to have a strong genetic factor (Pederick et al. 1984) combined with certain soil nutrient levels. Indeed, the research team was able to induce stem deformity by the application of high amounts of nitrogen (Hopmans et al. 1995). Solving stem deformity was critical to the success of plantations established on high growth site types. It is noteworthy that the deformity was first thought to be associated with Cu deficiency, but subsequent investigations demonstrated that high levels of available soil N was primarily responsible, and a special breed of pine seedlings was produced in nurseries using the genotypes that tolerated highly fertile sites.

The introduction of sustainable forest management (SFM) criteria and indicators presented new challenges for the softwood nutrition program. SFM inter alia required management practices that not only ensured the maintenance of productivity but also the efficient use of chemicals including fertilizers to minimize chemical usage. Fertilizer efficiency is a complex issue that requires studies on a range of forest soils, especially those low in organic matter, to minimize leaching of added nutrients.

Finally, it is widely recognized that the mass production of high-quality seedlings in nurseries is the backbone of a successful plantation program, whether for replanting harvested stands or to establish new plantations. Ongoing monitoring of the levels of nutrients from the four nurseries across Victoria during the Plantation Extension program was conducted to ensure that seedlings were not suffering from any nutrient deficiencies at the time of lifting and dispatch. The management of nurseries with contrasting soil types is a challenge, especially where a soil type presents issues such as poor drainage, low infiltration capacity and poor structure with inherently low fertility. The development of specific fertilizer regimes for each nursery based on their respective soils and nutrient status of seedlings was a significant step forward in the planation program (Hopmans and Flinn 1983). Many other strategically important issues associated with nutritional management of the plantation program are discussed in the article linked earlier.

References

Flinn, D.W., Hopmans, P., Farrell, P. W. and James, J.M. 1979. Nutrient loss from the burning of Pinus radiata logging residue. Aust. For. Res. 9: 17-23.

Flinn, D.W. and Waugh, R.J. 1983. Evaluation of gypsum and organic matter additions for improving soil structure in a radiate pine nursery at Benalla. Aust. J. Exp. Agric. Anim. Husb. 23:208-215.

Forestry Research No 3, March 1964, For. Comm. Vic., 33pp

Note: The main aim of these unpublished Divisional Research Reports was to advise staff on a quarterly basis of broad progress in a variety of research projects being undertaken by the Commission. The reports in full are provided on this site.

Forestry Research No 9, Sept. 1967, For. Comm. Vic., 26pp.

Hopmans, P. and Flinn, D.W. 1983. Nutrient requirements in three Victorian radiata pine nurseries with contrasting soils. Aust. For. 46: 111-117.

Hopmans, P., Kitching, M. and Croatto, G. 1995. Stem deformity in Pinus radiata plantations in south-eastern Aiustralia.2. Effects of availability of soil nitrogen and response to fertilizer and lime. Plant and Soil 175:31-44.

Hopmans, P. and Elms, S. 2009. Changes in total carbon and nutrients in soil profiles and accumulation in biomass after a 30-year rotation of Pinus radiata on podzolized sands: Impacts of intensive harvesting on soil reserves. For. Ecol. Manage. 258:2183-2193.

Pederick, L. A., Hopmans, P., Flinn, D.W. and Abbott, I.D. 1984. Variation in genotypic response to suspected copper deficiency in Pinus radiata. Aust. For. Res. 14:75-84.

Raupach, M., Clarke, A.R.P., Gibson, B.F. and Cellier, K.M. 1975. Cultivation and fertilizer effects on the growth and foliage nutrient concentrations of P.radiata, P. pinaster and P. caribaea on three soil types at Anglesea (Victoria). CSRIO Aust. Div. Soil Tech. Pap. No 25, 1-20.