Exchangeability of orthophosphate and pyrophosphate in soils: a double isotopic labelling study

Abstract

Liquid polyphosphate fertilisers have shown advantages in field experiments as a phosphorus (P) source for crops grown on calcareous soils. Polyphosphate fertilisers contain orthophosphate (oP), pyrophosphate (pP) and other condensed P species. A double labelling technique was developed using ion chromatography for separation of oP and pP, the major P species in polyphosphate fertilisers, in order to measure the isotopically exchangeable oP, pP and hydrolysed pP. Isotopically exchangeable P was measured in soils incubating for zero, three and 7 days after applying oP or pP to simulate a fertiliser band concentration at one g P kg −1 soil. The data from this incubation study suggest that pP addition initially resulted in less isotopically exchangeable P than oP addition but there was no significant difference in the total isotopically exchangeable P for the two different P sources after 7 days of incubation. The addition of pP to soil resulted in an increase in iron, aluminium and dissolved organic carbon in soil solution, and a decrease in calcium concentration in soil solution. This study has shown that the availability of P added as pP is governed by a complex series of processes that differ from the chemistry of oP reactions in soil.

Fate and bioavailability of phosphorus loaded to iron oxyhydroxide nanoparticles added to weathered soils

“…This is supported by previous results, where HMP in solution proved to almost completely (80%) bioavailable compared to KH2PO4 (Bollyn et al 2017). The presence of soil-borne microorganisms likely speeds up the hydrolysis, making HMP as bioavailable as KH2PO4, a result that was previously found for other polyphosphates (Dick 1985;McBeath et al 2009). To better understand the critical soil parameters that affect the stability of added P-loaded nanoparticles and native colloids, a fate study was set up in Part II examining the pore water composition under varying conditions.…”

Colloidal-Bound Polyphosphates and Organic Phosphates Are Bioavailable: A Nutrient Solution Study

“…12 All treatments were spiked with radioactive 33 P at a dose of 10 Bq mL −1 nutrient solution, so each pot received a total dose of 1.9 kBq. Colloidal stock suspensions were made by mixing different components in the following order under continuous stirring: water, colloid, NOM/HMP/IHP, P i , and 33 P i . The time between addition of stable and radioactive P never exceeded 1 min; this stock suspension was then added to aerated nutrient solutions to obtain the correct end concentration and equilibrated for at least 1 h before transplanting the seedlings.…”

Source and formulation matter: New insights into phosphorus fertilizer fate and transport in mildly calcareous soils

“…S7). How quickly the conversion of PP to OP proceeds in the field depends on environmental conditions such as temperature, soil type, P concentration, and pH (Dick and Tabatabai, 1986;McBeath et al, 2006;McBeath et al, 2009). One concern often raised is that because PP must go through this hydrolysis step for the nutrient to become useful to plants, early season growth may be compromised when this reaction is slow (McBeath et al, 2006).…”