Effects of fertiliser applications after thinning of Pinus radiata on a high-elevation site in south-eastern Australia

• Published in: Australian forestry Vol. 79; no. 3; pp. 196 - 202
• Main Authors: Green, Phil, Turner, John, Knott, Jim
• Format: Journal Article
• Language: English
• Published: Taylor & Francis 02.07.2016
• Subjects: Nitrogen; optimisation; phosphorus; thinning; values
• ISSN: 0004-9158; 2325-6087
• DOI: 10.1080/00049158.2016.1184832

A trial to assess the effects of fertiliser applied after thinning was established in a ten-year-old Pinus radiata stand growing on a high elevation site in south-eastern Australia. The trial had two components. The first studied the effects of fertilisers applied in a factorial design with two levels of phosphorus (0 and 50 kg P ha -1 ) and three of nitrogen (0, 150 and 300 kg N ha -1 ) plus a mixed nutrient treatment to areas thinned to a routine intensity. In the second part, levels of thinning intensity were assessed with and without a fertiliser (N 1 P 1 ) application. Over the seven years of the study, growth was affected by below average rainfall in four of the years. Significant responses to fertiliser were achieved with all treatments; the best was 150 kg N ha -1  + 50 kg P ha -1 plus trace elements. The volume increment was increased by 28%, however this was not significantly different from the N 1 P 1 alone. The N 1 P 1 fertiliser increased productivity at all thinning levels including the unthinned treatment. Models predicting relative growth response based on foliage nutrient levels gave reasonable predictions, that is, 29% increase in volume periodic increment and this was slightly higher than that achieved. On such low rainfall sites, rather than having multiple thinnings, one option is a relatively heavy thinning at a young age with fertiliser application and then leaving the stand until final harvest. Estate optimisation models provide forest managers with the means to evaluate fertiliser-thinning treatment options against objectives such as maximising the present value of expected future cash flow within production and budget constraints.