Optimising productivity and profitability through informed choices is the focus of a range of research projects around Australia to support hardwood plantations.
Optimising productivity of hardwood plantations
Researchers in one project collated the results of a wide range of trials and inventory data collected by hardwood growers across southern Australia, with a focus on E. globulus (blue gum) and E. nitens (Shining gum). The aim was to identify what contributed to the gaps between potential and operational yield in hardwood plantations.
The study, Optimising productivity of hardwood plantations: yield gap analysis for Eucalyptus globulus plantations in southern Australia, utilised the APSIM Eucalyptus process-based growth model and focused on the productivity of 10-year-old hardwood plantations.
The project aimed to improve grower knowledge underpinning decisions on the location and management of hardwood plantations across southern Australia. The analysis provided estimates of potential productivity, and determined the main causes of any shortfalls in actual yields, as well as the extent to which various management practices might be best used to reduce gaps. Key factors included:
- Climate, in particular water availability (influenced by annual rainfall, as well as regional differences such of temperature and evaporation) was the primary limit to productivity across southern Australia.
- Variation in potential rooting depth, as affected by soil properties, had an impact on potential yield.
- Greater yields could be attributed to plantations with access to additional water in the form of run-on, groundwater and deep-profile soil water.
- Low nitrogen availability and was strongly linked to land-use history, with average yield significantly less where land had not previously been used for agriculture.
- More minor impacts included weed competition in well-established plantations, stand density and subsequent competition-induced mortality.
Overall, the model simulations were useful in examining the role of individual factors affecting hardwood growth and yield. To offer further support, growers were provided with widespread industry training on the use of APSIM and access to a range of online resources.
“The hope is that, with ongoing support, hardwood producers will be able to easily adopt this current modelling capability, as well as embracing its future enhancements for improved decision-making and productivity in the long term,” said Dr John McGrath of McGrath Forestry Services, who was involved in the research.
The final report from this work was provided to FWPA by the research team in 2022 and will be reviewed, finalised and published in full later this year.
Optimising nutrition management of hardwood plantations
Field research during recent decades has provided insights into nutrition dynamics and other factors that impacted the productivity of hardwood plantations. Key issues for nutrient management are fertiliser use, retention of harvest residues, and weed control.
Managers generally use adequate levels of weed control in plantations, which has a strong basis in research. However, there remains a lack of reliable data for predictions about nutrient applications across a variety of multi-rotation hardwood sites.
“Process-based modelling can help support a better understanding of these issues, but onerous input requirements, alongside a lack of validation of these models in real-world situations, have resulted in low industry confidence when using them to inform fertiliser use decisions,” Dr McGrath said.
During the Optimising nutrition management of hardwood plantations for sustainable productivity and profitability project the research team established 45 nutrition trials within young hardwood plantations across southern Australia between 2018 and 2019.
While tools such as the FWPA-supported ProFert for Pine have helped improve the capacity of softwood growers to effectively predict the effectiveness of various fertiliser options at different sites, no such tool had yet been calibrated for hardwoods.
Hardwood plantation managers were seeking access to clearly articulated fertiliser guidelines for the timing and application of nutrients to maximise growth, and the best approaches for different situations.
The research team set out to establish a trial network designed to address these gaps in nutrition response knowledge through experiments relating to fertiliser rates and responsiveness.
“The goal was to use the results of this work, combined with data from past experiments, to develop tools that would allow hardwood plantation managers to better target their fertiliser and nutrient management practices on a site-specific basis for optimal responsiveness,” Dr McGrath said.
Based on results from the first three years of this research, the overall productivity of hardwood plantations and the response to nitrogen when applied to stands aged two to five years were strongly influenced by both temperature and water availability.
Where adequate supplies of nitrogen, phosphorus and potassium were applied, and water supply was high, the potential productivity of plantations more than doubled when temperatures increased from 14°C to 22°. However, where water supply was limited by rainfall and evaporation, productivity was found to be lower than the potential productivity at sites with the same temperature increase.
Significant responses were also observed around the application of nitrogen. Based on the trial data, applying 200 kg of nitrogen per hectare resulted in a 20 per cent average increase in production during the first two years following application. However, this declined to 16 per cent by year three. Notably, the annual responses to lower rates of nitrogen (50 and 100 kg of nitrogen per hectare) were lower, and these responses declined more quickly.
At sites where growth was limited by either lower temperatures or lack of water supply, the positive response to nitrogen was also generally found to be lower.
Based on growth responses during the first three years of this research, the team’s key recommendations are that application of 200 kg of nitrogen per hectare is ample for increased plantation productivity. Moreover, the strongest responses to nitrogen application tend to be observed at relatively warmer, wetter sites.
These findings have now been incorporated into the ProFert tool to provide estimates of the likely profitability of applying fertilisers to hardwood stands in southern Australia.
“While there are a considerable number of uncertainties and assumptions in these relationships, the resultant model is expected to provide a useful tool for growers,” said Dr Barry May of TreeMod, and the creator and developer of ProFert.
“ProFert represents a major improvement on current methods for identifying potentially responsive young stands to fertiliser and the ability to determine the optimum rate of fertiliser to apply.”
This updated version of ProFert has been provided to growers for testing and is expected to be refined and improved based on feedback and the incorporation of results from the continuing project.
The final report for this project, which covers the first three years of results post-treatment, is in the final stages of preparation.
Enhancing the knowledge base
This work is set to continue with the Enhancing the knowledge base for hardwood plantation management project, which began in the spring of 2022.
The research aims to provide a mechanism to continue garnering information from the network of nutrition trials installed between 2018 and 2019 through to the end of rotation by reconfiguring them to provide additional insights into effective nutrient management in hardwood plantations for maximum productivity and profitability.
“The data synthesis component of this continued work has an additional objective of storing all data accumulated for potential future use. The hope is this will provide a strong legacy based on the efforts of the numerous organisations and people who have been involved in the establishment, maintenance and analysis of these, and a wide range of earlier trials,” Dr McGrath said.
Dr McGrath concluded by saying that, as well as the ongoing trials, this project – aimed at enhancing the knowledge base – will access and synthesise data from a wide range of prior experiments and trials set up by a range of agencies.
