Turner and Blackwell (European Journal of Soil Science; 2013) studied the pH effect on the organic phosphorus speciation using the unique acid gradient strip on a soil fertilization / exhaustion long-term experiment (Hoosfield) at Rothamsted Research, Harpenden, UK. This experimental site offered a singular opportunity to study a wide pH gradient in a single soil type that has been under uniform land use for 150 years. The soil acidification caused by progressive leaching of bases was associated with a reduction on soil carbon and a relative increase in organic phosphorus. Among the main findings, the authors reported that inositol phosphates, DNA and phosphonates were preferentially accumulated under acidic conditions. Possible causes to the observed behaviour were: a) metal chelation of inorganic phosphorus compounds; b) chemical interactions between organic phosphorus compounds and clay surfaces; c) pH dependency of soil phosphatase enzymes; d) Phosphatases inactivation by sorption; e) differential abundance of organisms that synthesize phosphatases. The acid pHs strongly limited barley growth and therefore the P extraction and cycling; therefore the observed results are not just a function of soil chemical factors, but were most likely were also a function of the complex interactions and mass balances associated with the different plant growth and survival across the studied acid strip.
This study brings new insights about the effect of long term soil acidification on the abundance of different forms of soil phosphorus. The issues involved are transversal to soil P fertilizer application and management strategies in agricultural soils.