There are strong links between the physical, chemical and biological properties of soil and forest performance. Topsoil depth, soil structure, rooting depth, hard pans, texture, water holding capacity and nutrient supply all affect the full potential of a forest and the ability of the land to support long-term sustainable production.
Scion soil scientists are constantly seeking to understand more about the effect of forest management practices on soil, its microbial communities, and processes that control soil and forest productivity. We are also the guardians of the National Forest Soil Archive.
Improving soil nutrition
Many of New Zealand’s plantation forests have nutrient deficiencies or imbalances. Determining what that imbalance is, and treating it prior to planting, can help achieve optimal tree growth.Our work focusses on managing soil nutrients for optimum growth over repeated forestry rotations.
Boron deficiency is the most widespread micro-nutrient deficiency in New Zealand forests, causing the death of terminal buds and shoots, and stem malformation. Work carried out under the Growing confidence in forestry's future programme has shown that boron fertiliser not only prevents tree deformation but also promotes growth. The recommended application rates differ for different species. Where 4-8 kg per hectare of boron produced the greatest growth rate in radiata pine, applying 4 kg/ha to young Douglas-fir reduced growth. A lower rate of 1-2 kg/ha is more appropriate for this species.
The Nutrient Balance Model NuBalM
NuBalM is a tool that can be used to predict nutrient supply over multiple forestry rotations. Find out more about precision nutrient management for maximum productivity.
Fertiliser application can improve the productivity and, potentially, the sustainability radiata pine growing in New Zealand. Fertiliser is routinely used in locations where critical nutrient deficiencies can be addressed in a cost-effective manner. However, there is uncertainty around the cost of fertilising and concern about negative impacts on wood properties. We are conducting research to improve the predictions of fertiliser response and test the effectiveness of new application methods. We are also looking at potential consequences for wood properties and the wider environmental and regulatory issues associated with nutrient applications
As an example of our work, an analysis of growth, nutrition and climatic data from several existing fertiliser trials has determined that soil phosphorus and moisture availability can produce relatively accurate predictions of growth following the application of fertiliser.
More than 50% of New Zealand's planted forest estate will soon be in its third or fourth rotation.Successful successive rotations of radiata pine depend on soils that can provide nutrients long term. However, there is limited data as to how these affect soils and how soil nutrient levels can be maintained. Preliminary results over two rotations in the Woodhill Forest suggest that retaining the forest floor and harvest residue benefits the soil carbon and nitrogen content more than adding fertiliser. This work is continuing.
Soil microbial communities
The makeup of soil microbial communities and their activity can affect forest growth. Learning more about the relationship between soil biodiversity and tree health is helping us improve tree growth and health, and future proof both planted forests and wider plant ecosystems against climate change.
Understanding how site preparation and identifying the environmental factors that influence the abundance and activity of beneficial soil microbes will allow us to develop management systems for forest soils that enhance the benefits provided by soils and the resident microbial community.
Our research into the complex relationship between plants, microbes and soil systems is shedding light on how plants cope with environmental stresses, such as drought or extreme rain, and what implications this may have as the climate warms.
Scion uses soil molecular research and genetic sequencing to identify genes that give soil microbes the ability to enhance forest performance through increasing stress tolerance and making nitrogen more available. We are also looking at how radiata genotypes influence the activity of soil microbes.
The initial results suggest that this interaction with microorganisms can help explain why some genotypes are more tolerant to harsh conditions than others, which may explain how some tree species can establish more rapidly in marginal land.
Beneficial mycorrhizal fungi contribute to the soil microbial communities. Our work has shown that reducing the use of fungicides and fertiliser actually enhances the growth of seedling radiata pine.
Simeon Smaill, Assistant Research Leader, Soil Plant Ecology
Soil testing and analytics
Many of New Zealand’s plantation forests have a nutrient deficiency or imbalance. Determining what that imbalance is, and treating it prior to planting, can help ensure optimal tree growth is achieved.
A soil analysis can be used to define possible reasons for nutrient deficiencies or imbalances at any stage in the forestry life cycle.
Scion’s analytical chemistry laboratory, Veritec, specialises in forestry related samples and material testing, and provides a range of analytical services on soils.
See Veritec laboratory services for further details.
Information on sampling forest soils can be found on the Growing confidence in forestry's future website.