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P-fertilisation trial

Project leader, researchers and collaborators: Dr Catriona Macdonald, Dr Yolima Carrillo, Prof Elise Pendall, Prof Jeff Powel, Assoc Prof Uffe Nielsen, Prof Sally Power, Prof David Ellsworth, Dr Kristine Crous

Funding period: 

Project summary: The goal of this project is to evaluate the impact of different P fertiliser additions on soil nutrient pools and microbial processes at three different locations with differing soil texture within the EucFACE site.

As the EucFACE research facility moves towards a P-intervention phase of the field experiment, there remains numerous unknowns about how P is cycled within this ecosystem.  This makes it challenging to identify a P-fertilization approach that will ensure successful implementation (ecosystem response) of this phase of the experiment, while minimizing undesirable effects on below ground soil communities resulting from fertilizer addition.

One of the major unknowns related to P at the site is process rates at depth.  Limited work at depth has demonstrated appreciable levels of total P (to 30 cm) at depth within these soils (J Pilhblad).  Taken together with an active microbial and root biomass to 30 cm (and beyond; see Table 1), there remains several unknowns about the rate of change of P between different pools in deeper soil layers within the site and how these pools might be affected by a P addition experiment.  Addressing some of these unknowns will (i) help better understand P cycling within the EucFACE ecosystem, (ii) better inform prediction models (iii) help inform a P-fertilisation intervention.

The heterogeneity of soil and plant components at the site make applying a fertilizer treatment challenging.  For example, different textural composition across the six treatment rings leads to a different phosphorus buffering index for each ring, which ultimately influences P-availability for plant uptake.  P-sorption ranges from 0–27 % across the site. Different tree and shrub densities and different levels of ground cover across rings and within rings, also leads to the need for careful consideration when developing a P-fertilization plan. 

As the current proposed P-fertilization experiment will likely involve fertilization of one of three paired rings (yet to be determined), it is important to understand short and mid-term effects of P addition to the site at the ring level.