Soils Lab

Tegan Darch

Tegan Darch

Phosphorus is an essential element for all living cells, and is often considered to be the limiting nutrient in tropical soils due to the low prevalence of the most plant-available form, inorganic phosphorus.  However, application of phosphorus fertilizers to tropical forest soils has often shown no effect on tree growth.  On the other hand, removal of leaf litter from the soil surface can decrease organic phosphorus in the soil, indicating that plants are able to access phosphorus from this largely overlooked pool.

As part of my PhD, I spent 3 months at STRI collaborating with Dr Ben Turner, in order to determine the proportion of soil organic phosphorus which is potentially bioavailable to plants and microorganisms.  To answer this, I first developed a protocol for extracting the same phosphorus from the soil that plants are able to, by using organic acids, which are compounds that plants exude to solubilise phosphorus.  For organic phosphorus to be bioavailable, it must be amenable to hydrolysis by extracellular enzymes, and I therefore determined the proportion of plant available organic phosphorus by further developing and applying an enzyme hydrolysis method to the soil extracts.

Initial results indicate that the organic acids not only extract more phosphorus from the soil than water, but that the phosphorus extracted comes from a different pool, as a greater proportion of it is bioavailable.  In all of the soils tested, organic phosphorus comprised the majority of the total phosphorus in the soil, and the quantity of enzyme hydrolysable organic phosphorus was not significantly different to inorganic phosphorus.  Therefore, the pool of organic phosphorus is potentially very significant in the phosphorus nutrition of tropical forests.  

Academic record:

2009 – Present.  PhD student, Rothamsted Research, North Wyke (UK) and Lancaster University
2008 – 2009.  MSc in Soils and Contaminated Land, Reading University
2005 – 2008.  Laboratory technician at the Institute of Child Health, University College London
2002 – 2005.  BSc in Environmental Chemistry


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