The findings from a major study into applying fertiliser to radiata pine forests have been used to create a computer model that helps forest managers increase both the yield and profitability of wood production.
The decision support system has been developed by scientists from Ensis funded by the Forests and Wood Products Research and Development Corporation (FWPRDC) in collaboration with Auspine, Forestry SA and Green Triangle Forest Products. It is based on data from experiments carried out over 12 years at 16 sites in the Green Triangle region in South Australia and Victoria.
The computer model integrates the results from these experiments to predict the growth response and profitability of different rates, forms and application scenarios for nitrogen and phosphorous fertiliser. The goal is to help forest managers maximise wood production or profit. While simple too use, the system is underpinned by a detailed scientific understanding of the key processes influencing soil nutrient supply and how this drives tree growth.
Inputs for the model include basic information such as stocking, age, volume and site quality while outputs include graphs of annual or cumulative response, harvest yield, actual and discounted fertiliser costs and indications of harvest revenues.
Ensis Forest Scientist Dr Barrie May, who helped develop the decision support system, says it gives forest managers a simple, user-friendly tool to rapidly and automatically identify the optimum fertiliser strategy for a particular site as well as a way to compare relative growth responses and profitability across multiple sites.
“Overall it provides a means to substantially improve fertiliser efficiency by targeting stands that will respond to fertiliser application and then highlighting strategies to boost growth and maximise wood yield using fertiliser regimes,” Dr May says.
Dr May says while the model is yet to be tested outside the Green Triangle, he is confident many of its predictive capabilities will be transferable, with appropriate customisation.
Results from the research underpinning the new computer model found that growth over six years on plots fertilised with both nitrogen and phosphorous increased by 8 to 28 m3 ha-1, compared with unfertilised plots. An economic analysis showed that this translated to returns on investment ranging from -2 per cent to 39 per cent as a result of the increase in tree size which, in turn, boosted both the volume and unit value of the wood produced.
“The findings show how the efficiency and profitability of fertiliser application can be improved by targeting the most responsive sites and tailoring fertiliser strategies to suit requirements of specific stands,” Dr May says.
For example, he says, applying nitrogen to stands previously fertilised with phosphorous increased the average stand value by almost double compared with applying nitrogen (N) alone to unfertilised stands. The findings have also shown that most sites in the Green Triangle do not respond to phosphorous (P) alone and there is little benefit in applying P more frequently than once every ten years at most sites.
Dr May says the number of sites tested and the detailed information gathered at them since the mid 1990s make the research one of the largest and most significant long term studies of response to fertiliser and N and P cycling ever carried out in Australia.
The findings have delivered other valuable information including evidence that some forms of nitrogen are more effective than others. Dr May says responses to nitrogen applied as urea were significantly lower – on average around 30 per cent - than ammonium nitrate or ammonium sulphate. However, certain forms of urea, such as agrotain urea, showed promising results.
Dr May says foresters have, in the past, tended to assume fertiliser application was straightforward but the research results prove otherwise.
“If you choose the wrong fertiliser or wrong site, the trees may actually grow more slowly than if you did nothing,” he says.
“Furthermore, if you wait too long before thinning or clear felling fertilised stands much of the early fertiliser response may be eroded as a result of other factors limiting growth. However, the right applications combined with the appropriate silviculture regime can lead to a significant increase in wood production and, ultimately, greater returns. There has been a lot of guesswork in the past – now we have a means of quantifying the inputs and returns.”
Editor's Note: Original news release can be found here.